
comp.vuw.ac.nz!zephyr.grace.cri.nz!usenet



Archive-name: autos/gasoline-faq/part1

           FAQ: Automotive Gasoline
                  Bruce Hamilton
                B.Hamilton@irl.cri.nz

Changes: 
Updated Section 5.1 with 1994 vehicle production data.
Updated Section 5.14 with new table and references.
Several recent references also added to other sections.

------------------------------


1.1  Introduction and Intent

The intent of this FAQ is to provide some basic information on gasolines 
and
other fuels for spark ignition engines used in automobiles. The toxicity 
and 
environmental reasons for recent and planned future changes to gasoline 
are
discussed, along with recent and proposed changes in composition of 
gasoline.
This FAQ is intended to help readers choose the most appropriate fuel 
for 
vehicles, assist with the diagnosis of fuel-related problems, and to 
understand the significance of most gasoline properties listed in fuel 
specifications. I make no apologies for the fairly heavy emphasis on 
chemistry; it is the  only sensible way to describe the oxidation of 
hydrocarbon fuels to produce energy, water, and carbon dioxide.

1.2  Abbreviations

AKI = Anti-Knock Index of Gasoline ( RON+MON/2 )
CI = Compression Ignition ( Diesel )
Gasoline = Petrol ( Yes, complaints were received :-) )
IC = Internal Combustion
MON = Motor Octane Rating
Octane = The Octane Rating of the Gasoline 
RFG = Reformulated Gasoline ( as defined by US Clean Air Act )
RON = Research Octane Rating
SI = Spark Ignition ( Gasoline )

------------------------------


        1. Introduction and Intent
        2. Table of Contents
        3. What Advantage will I gain from reading this FAQ?
        4. What is Gasoline?
          4.1  Where does crude oil come from?.
          4.2  When will we run out of crude oil?.
          4.3  What is the history of gasoline?     
          4.4  What are the hydrocarbons in gasoline?
          4.5  What are oxygenates?
          4.6  Why were alkyl lead compounds added?
          4.7  Why not use other organometallic compounds?
          4.8  What do the refining processes do?
          4.9  What energy is released when gasoline is burned?
          4.10 What are the gasoline specifications?
          4.11 What are the effects of the specified fuel properties? 
          4.12 Are brands different?
          4.13 What is a typical composition?
          4.14 Is gasoline toxic or carcinogenic? 
          4.15 Is unleaded gasoline more toxic than leaded?
          4.16 Is reformulated gasoline more toxic than unleaded? 
          4.17 Are all oxygenated gasolines also reformulated gasolines?  
        5. Why is Gasoline Composition Changing?
          5.1  Why pick on cars and gasoline? 
          5.2  Why are there seasonal changes?
          5.3  Why were alkyl lead compounds removed?
          5.4  Why are evaporative emissions a problem?
          5.5  Why control tailpipe emissions?
          5.6  Why do exhaust catalysts influence fuel composition?
          5.7  Why are "cold start" emissions so important?
          5.8  When will the emissions be "clean enough"?
          5.9  Why are only some gasoline compounds restricted?
          5.10 What does "renewable" fuel/oxygenate mean?
          5.11 Will oxygenated gasoline damage my vehicle?
          5.12 What does "reactivity" of emissions mean?
          5.13 What are "carbonyl" compounds?
          5.14 What are "gross polluters"? 
        6. What do Fuel Octane ratings really indicate?
          6.1  Who invented Octane Ratings?
          6.2  Why do we need Octane Ratings?
          6.3  What fuel property does the Octane Rating measure?
          6.4  Why are two ratings used to obtain the pump rating?
          6.5  What does the Motor Octane rating measure?
          6.6  What does the Research Octane rating measure?
          6.7  Why is the difference called "sensitivity"?
          6.8  What sort of engine is used to rate fuels?
          6.9  How is the Octane rating determined?
          6.10 What is the Octane Distribution of the fuel?
          6.11 What is a "delta Research Octane number"?
          6.12 How do other fuel properties affect octane?
          6.13 Can higher octane fuels give me more power?
          6.14 Does low octane fuel increase engine wear?
          6.15 Can I mix different octane fuel grades?
          6.16 What happens if I use the wrong octane fuel?
          6.17 Can I tune the engine to use another octane fuel?
          6.18 How can I increase the fuel octane?
          6.19 Are aviation gasoline octane numbers comparable?        
          6.20 Can mothballs increase octane? 
        7. What parameters determine octane requirement?
          7.1  What is the effect of Compression ratio?
          7.2  What is the effect of changing the air/fuel ratio?
          7.3  What is the effect of changing the ignition timing
          7.4  What is the effect of engine management systems?
          7.5  What is the effect of temperature and Load?  
          7.6  What is the effect of engine speed?
          7.7  What is the effect of engine deposits?
          7.8  What is the Road octane requirement of an vehicle?
          7.9  What is the effect of air temperature?.
          7.10 What is the effect of altitude?.
          7.11 What is the effect of humidity?.
          7.12 What does water injection achieve?.
        8. How can I identify and cure other fuel-related problems?
          8.1  What causes an empty fuel tank?
          8.2  Is knock the only abnormal combustion problem?        
          8.3  Can I prevent carburetter icing?
          8.4  Should I store fuel to avoid the oxygenate season?
          8.5  Can I improve fuel economy by using quality gasolines?
          8.6  What is "stale" fuel, and should I use it?
          8.7  How can I remove water in the fuel tank?
          8.8  Can I use unleaded on older vehicles?
          8.9  How serious is valve seat recession on older vehicles? 
        9. Alternative Fuels and Additives
          9.1  Do fuel additives work?
          9.2  Can a quality fuel help a sick engine?
          9.3  What are the advantages of alcohols and ethers?
          9.4  Why are CNG and LPG considered "cleaner" fuels.
          9.5  Why are hydrogen-powered cars not available?
          9.6  What are "fuel cells" ?
          9.7  What is a "hybrid" vehicle?
          9.8  What about other alternative fuels?
          9.9  What about alternative oxidants?
       10. Historical Legends
         10.1  The myth of Triptane
         10.2  From Honda Civic to Formula 1 winner.                    
       11. References
         11.1  Books and Research Papers
         11.2  Suggested Further Reading
         
------------------------------


This FAQ is intended to provide a fairly technical description of what 
gasoline contains, how it is specified, and how the properties affect 
the 
performance of your vehicle. The regulations governing gasoline have 
changed, and are continuing to change. These changes have made much of 
the 
traditional lore about gasoline obsolete. Motorists may wish to 
understand 
a little more about gasoline to ensure they obtain the best value, and 
the 
most appropriate fuel for their vehicle. There is no point in 
prematurely 
destroying your second most expensive purchase by using unsuitable fuel, 
just as there is no point in wasting hard-earned money on higher octane
fuel that your automobile can not utilize. Note that this FAQ does not
discuss the relative advantages of specific brands of gasolines, it is 
only intended to discuss the generic properties of gasolines.

------------------------------


4.1  Where does crude oil come from?.

The generally-accepted origin of crude oil is from plant life up to 3 
billion years ago, but predominantly from 100 to 600 million years ago 
[1]. 
"Dead vegetarian dino dinner" is more correct than "dead dinos".
The molecular structure of the hydrocarbons and other compounds present 
in fossil fuels can be linked to the leaf waxes and other plant 
molecules of 
marine and terrestrial plants believed to exist during that era. There 
are 
various biogenic marker chemicals such as isoprenoids from terpenes, 
porphyrins and aromatics from natural pigments, pristane and phytane 
from 
the hydrolysis of chlorophyll, and normal alkanes from waxes, whose size 
and shape can not be explained by known geological processes [2]. The 
presence of optical activity and the carbon isotopic ratios also 
indicate a 
biological origin [3]. There is another hypothesis that suggests crude 
oil 
is derived from methane from the earth's interior. The current main 
proponent of this abiotic theory is Thomas Gold, however abiotic and
extraterrestrial origins for fossil fuels were also considered at the 
turn 
of the century, and were discarded then. A large amount of additional
evidence for the biological origin of crude oil has accumulated, however
Professor Gold still actively promotes his theory worldwide, even though
it does not account for the location and composition of all crude oils.  

4.2  When will we run out of crude oil?

It has been estimated that the planet contains over 1.4 x 10^15 tonnes 
of 
petroleum, however much of this is too dilute or inaccessible for 
current 
technology to recover [4]. The petroleum industry uses a measure called 
the Reserves/Production ratio (R/P) to monitor how production and 
exploration are linked. This is based on the concept of "proved" 
reserves 
of crude oil, which are generally taken to be those quantities which 
geological and engineering information indicate with reasonable 
certainty 
can be recovered in the future from known reservoirs under existing 
economic
and operating conditions. The Reserves/Production ratio is the above 
reserves divided by the production in the last year, and the result is 
the 
length of time that those remaining reserves would last if production 
were 
to continue at the current level [5]. It is important to note those 
definitions, as the price of oil increases, marginal fields become 
"proved 
reserves", thus we are unlikely to "run out" of oil, as more fields will 
become economic as the price rises. The US Geological Survey has just
increased their assessment of US available oil by 60 billion barrels, 
thus
increasing the R/P from 9.9 to 27 years [6]. They also doubled the
size of the gas reserves to 9.1 trillion cubic metres. If the price 
exceeds 
$30/bbl then alternative fuels may become competitive, and at $50-60/bbl 
coal-derived liquid fuels are economic, as are many biomass-derived 
fuels 
and other energy sources [7].  The current price for Brent Crude is 
approx. 
$18/bbl. The world R/P ratio has increased from 27 years (1979) to 43.1 
years
(1993). I have retained the BP data for the US in the Table below, as 
well as
including the new USGS numbers. [5,6]. One billion = 1 x 10^9. One 
trillion = 1 x 10^12. One barrel of oil = 0.158987 m3 and 0.136 tonnes - 
for 
a typical Arabian Light oil.

Crude Oil              Proved Reserves                  R/P Ratio
Middle East                89.6 billion tonnes           95.1 year
USA                         4.0                           9.9 years
USA - 1995 USGS data       10.9                          33.0 years
Total World               136.7                          43.1 years

Coal                   Proved Reserves                  R/P Ratio
USA                       240.56 billion tonnes         267 years
Total World             1,039.182                       236 years

Natural Gas            Proved Reserves                  R/P Ratio 
USA                         4.7 trillion cubic metres     8.8 years
USA - 1995 USGS data        9.1                          17.0 years
Total World               142.0                          64.9 years.

4.3  What is the history of gasoline? 

In the late 19th Century the most suitable fuels for the automobile
were coal tar distillates and the lighter fractions from the 
distillation
of crude oil. During the early 20th Century the oil companies were
producing gasoline as a simple distillate from petroleum, but the
automotive engines were rapidly being improved and required a more
suitable fuel. During the 1910s, laws prohibited the storage of 
gasolines
on residential properties, so Charles F. Kettering ( yes - he of 
ignition
system fame ) modified an IC engine to run on kerosine. However the
kerosine-fuelled engine would "knock" and crack the cylinder head and
pistons. He assigned Thomas Midgley Jr. to confirm that the cause was
from the kerosine droplets vaporising on combustion as they presumed . 
Midgley demonstrated that the knock was caused by a rapid rise in
pressure after ignition, not during preignition as believed [8]. This
then lead to the long search for anti-knock agents, culminating in
tetra ethyl lead [9]. Typical mid-1920s gasolines were 40 - 60 Octane 
[10]. 

Because sulfur in gasoline inhibited the octane-enhancing effect 
of the alkyl lead, the sulfur content of the thermally-cracked refinery 
streams for gasolines was restricted. By the 1930s, the petroleum
industry had determined that the larger hydrocarbon molecules (kerosine)
had major adverse effects on the octane of gasoline, and were developing
consistent specifications for desired properties. By the 1940s catalytic 
cracking was introduced, and gasoline compositions became fairly 
consistent
between brands during the various seasons.

The 1950s saw the start of the increase of the compression ratio, 
requiring
higher octane fuels. Lead levels were increased, and some new refining 
processes ( such as hydrocracking ), specifically designed to provide 
hydrocarbons components with good lead response and octane, were 
introduced.
Minor improvements were made to gasoline formulations to improve yields 
and 
octane until the 1970s - when unleaded fuels were introduced to protect 
the exhaust catalysts that were also being introduced for environmental 
reasons. From 1970 until 1990 gasolines were slowly changed as lead was 
phased out. In 1990, the US Clean Air Act started forcing major 
compositional 
changes on gasoline, and these changes will continue into the 21st 
Century 
because gasoline is a major pollution source.

The move to unleaded fuels continues worldwide, however several 
countries
have increased the aromatics content ( up to 50% ) to replace the alkyl 
lead octane enhancers. These highly aromatic gasolines can result in 
in damage to elastomers and increased levels of toxic aromatic emissions 
if used without exhaust catalysts.

4.4  What are the hydrocarbons in gasoline?

Hydrocarbons ( HCs ) are any molecules that just contain hydrogen and
carbon, both of which are fuel molecules that can be burnt ( oxidised )
to form water ( H2O ) or carbon dioxide ( CO2 ). If the combustion is 
not complete, carbon monoxide ( CO ) may be formed. As CO can be burnt
to produce CO2, it is also a fuel.

The way the hydrogen and carbons hold hands determines which hydrocarbon
family they belong to. If they only hold one hand they are called
"saturated hydrocarbons" because they can not absorb additional 
hydrogen.
If the carbons hold two hands they are called "unsaturated hydrocarbons" 
because they can be converted into "saturated hydrocarbons" by the
addition of hydrogen to the double bond. Hydrogens are omitted from the 
following, but if you remember C = 4 hands, H = 1 hand, and O = 2 hands, 
you can draw the full structures of most HCs. 

Gasoline contains over 500 hydrocarbons that may have between 3 to 12 
carbons, and gasoline used to have a boiling range from 30C to 220C at 
atmospheric pressure. The boiling range is narrowing as the initial 
boiling 
point is increasing, and the final boiling point is decreasing, both 
changes are for environmental reasons. Detailed descriptions of 
structures 
can be found in any chemical or petroleum text discussing gasolines 
[11].

4.4.1 Saturated hydrocarbons ( aka paraffins, alkanes ) 

- stable, the major component of leaded gasolines.
- tend to burn in air with a clean flame.
- octane ratings depend on branching and number of carbon atoms.

alkanes 
  normal = continuous chain of carbons ( Cn H2n+2 )
  - low octane ratings, decreasing with carbon chain length.

    normal heptane C-C-C-C-C-C-C                    C7H16
  
  iso = branched chain of carbons  ( Cn H2n+2 )
  - higher octane ratings, increasing with carbon chain branching.
 
    iso octane =                       C   C   
    ( aka 2,2,4-trimethylpentane )     |   |
                                     C-C-C-C-C           C8H18   
                                       |
                                       C

  cyclic = circle of carbons  ( Cn H2n )
  ( aka Naphthenes )       
  - high octane ratings.
                 
    cyclohexane  =                 C
                                  / \
                                 C   C
                                 |   |                   C6H12
                                 C   C
                                  \ /
                                   C

4.4.2 Unsaturated Hydrocarbons

- Unstable, are the remaining component of gasoline.
- Tend to burn in air with a smoky flame.

Alkenes ( aka olefins, have carbon=carbon double bonds )         
- These are unstable, and are usually limited to a few %.
- tend to be reactive and toxic, but have desirable octane ratings.

                                 C
                                 |                       C5H10
          2-methyl-2-butene    C-C=C-C     

Alkynes ( aka acetylenes, have carbon-carbon triple bonds )
- These are even more unstable, are only present in
  trace amounts, and only in some poorly-refined gasolines.
                                 _
          Acetylene             C=C                      C2H2
 
Arenes  ( aka aromatics )
- Used to be up to 40%, gradually being reduced to <20% in the US.
- tend to be more toxic, but have desirable octane ratings.
- Some countries are increasing the aromatic content ( up to 50% in some
  super unleaded fuels ) to replace the alkyl lead octane enhancers.
 
                        C                       C  
                      // \                    // \
                     C    C                C-C    C
           Benzene   |   ||      Toluene     |   || 
                     C    C                  C    C
                      \\ /                    \\ /
                        C                       C

                      C6H6                    C7H8
 
Polynuclear Aromatics   ( aka PNAs or PAHs )
- These are high boiling, and are only present in small amounts in 
gasoline. 
  They contain benzene rings joined together. The simplest, and least 
toxic, 
  is Naphthalene, which is only present in trace amounts in traditional 
  gasolines, and even lower levels are found in reformulated gasolines. 
  The larger multi-ringed PNAs are highly toxic, and are not present in 

_
                                                                                                      

  gasoline.

                                  C   C        
                                // \ / \\         
                               C    C    C      
           Naphthalene         |    ||   |               C10H8
                               C    C    C
                                \\ / \ //
                                  C   C
 
4.5  What are oxygenates?

Oxygenates are just preused hydrocarbons :-). They contain oxygen, which 
can 
not provide energy, but their structure provides a reasonable anti-knock 
value, thus they are good substitutes for aromatics, and they may also 
reduce
the smog-forming tendencies of the exhaust gases [12]. Most oxygenates 
used 
in gasolines are either alcohols ( Cx-O-H ) or ethers (Cx-O-Cy), and 
contain 
1 to 6 carbons. Alcohols have been used in gasolines since the 1930s, 
and
MTBE was first used in commercial gasolines in Italy in 1973, and was 
first
used in the US by ARCO in 1979. The relative advantages of aromatics and 
oxygenates as environmentally-friendly and low toxicity octane-enhancers 
are 
still being researched.

    Ethanol                                  C-C-O-H      C2H5OH
  
                                               C
                                               |
    Methyl tertiary butyl ether              C-C-O-C      C4H90CH3
    (aka tertiary butyl methyl ether )         |
                                               C

They can be produced from fossil fuels eg methanol (MeOH), methyl 
tertiary 
butyl ether (MTBE), tertiary amyl methyl ether (TAME), or from biomass, 
eg 
ethanol(EtOH), ethyl tertiary butyl ether (ETBE)). MTBE is produced by 
reacting methanol ( from natural gas ) with isobutylene in the liquid 
phase 
over an acidic ion-exchange resin catalyst at 100C. The isobutylene was 
initially from refinery catalytic crackers or petrochemical olefin 
plants, 
but these days larger plants produce it from butanes. MTBE production 
has 
increased at the rate of 10 to 20% per year, and the spot market price 
in 
June 1993 was around $270/tonne [12]. The  "ether" starting fluids for 
vehicles are usually diethyl ether (liquid) or dimethyl ether (aerosol). 
Note that " petroleum ethers " are volatile alkane hydrocarbon 
fractions, 
they are not a Cx-O-Cy compound.

Oxygenates are added to gasolines to reduce the reactivity of emissions,
but they are only effective if the hydrocarbon fractions are carefully 
modified to utilise the octane and volatility properties of the 
oxygenates.
If the hydrocarbon fraction is not correctly modified, oxygenates can 
increase the undesirable smog-forming and toxic emissions. Oxygenates do 
not 
necessarily reduce all exhaust toxins, nor are they intended to.

Oxygenates have significantly different physical properties to 
hydrocarbons,
and the levels that can be added to gasolines are controlled by the EPA 
in
the US, with waivers being granted for some combinations. Initially the
oxygenates were added to hydrocarbon fractions that were slightly-
modified
unleaded gasoline fractions, and these were commonly known as 
"oxygenated"
gasolines. In 1995, the hydrocarbon fraction was significantly modified, 
and
these gasolines are called "reformulated gasolines" ( RFGs ). The change 
to
reformulated gasoline requires oxygenates to provide octane, but also 
that 
the hydrocarbon composition of RFG must be significantly more modified 
than 
the existing oxygenated gasolines to reduce unsaturates, volatility, 
benzene,
and the reactivity of emissions.

Oxygenates that are added to gasoline function in two ways. Firstly they
have high blending octane, and so can replace high octane aromatics
in the fuel. These aromatics are responsible for disproportionate 
amounts
of CO and HC exhaust emissions. This is called the "aromatic 
substitution 
effect". Oxygenates also cause engines without sophisticated engine 
management systems to move to the lean side of stoichiometry, thus 
reducing 
emissions of CO ( 2% oxygen can reduce CO by 16% ) and HC ( 2% oxygen 
can 
reduce HC by 10%)[13]. However, on vehicles with engine management 
systems,
the fuel volume will be increased to bring the stoichiometry back to
the preferred optimum setting. Oxygen in the fuel can not contribute 
energy, consequently the fuel has less energy content. For the same
efficiency and power output, more fuel has to be burnt, and the slight
improvements in combustion efficiency that oxygenates provide on some 
engines usually do not completely compensate for the oxygen.
 
There are huge number of chemical mechanisms involved in the pre-flame 
reactions of gasoline combustion. Although both alkyl leads and 
oxygenates 
are effective at suppressing knock, the chemical modes through which 
they 
act are entirely different. MTBE works by retarding the progress of the 
low 
temperature or cool-flame reactions, consuming radical species, 
particularly 
OH radicals and producing isobutene. The isobutene in turn consumes 
additional OH radicals and produces unreactive, resonantly stabilised 
radicals such as allyl and methyl allyl, as well as stable species such 
as 
allene, which resist further oxidation [14,15]. 

4.6  Why were alkyl lead compounds added?

The efficiency of a spark-ignited gasoline engine can be related to the
compression ratio up to at least compression ratio 17:1 [16]. However 
any
"knock" caused by the fuel will rapidly mechanically destroy an engine, 
and 
General Motors was having major problems trying to improve engines 
without 
inducing knock. The problem was to identify economic additives that 
could 
be added to gasoline or kerosine to prevent knock, as it was apparent 
that
engine development was being hindered. The kerosine for home fuels soon 
became a secondary issue, as the magnitude of the automotive knock 
problem 
increased throughout the 1910s, and so more resources were poured into 
the 
quest for an effective "anti-knock". A higher octane aviation gasoline 
was 
required urgently once the US entered WWI, and almost every possible 
chemical ( including melted butter ) was tested for anti-knock ability 
[17]. 

Originally, iodine was the best anti-knock available, but was not a 
practical
gasoline additive, and was used as the benchmark. In 1919 aniline was 
found
to have superior antiknock ability to iodine, but also was not a 
practical
additive, however aniline became the benchmark anti-knock, and various 
compounds were compared to it. The discovery of tetra ethyl lead, and 
the 
scavengers required to remove it from the engine were made by teams lead 
by 
Thomas Midgley Jr. in 1922 [8,9,17]. They tried selenium oxychloride 
which 
was an excellent antiknock, however it reacted with iron and "dissolved" 
the 
engine. Midgley was able to predict that other organometallics would 
work, 
and slowly focused on organoleads. They then had to remove the lead, 
which 
would otherwise accumulate and coat the engine and exhaust system with 
lead. 
They discovered and developed the halogenated lead scavengers that are 
still 
used in leaded fuels. The scavengers, ( ethylene dibromide and ethylene 
dichloride ), function by providing halogen atoms that react with the 
lead 
to form volatile lead halide salts that can escape out the exhaust. The 
quantity of scavengers added to the alkyl lead concentrate is calculated
according to the amount of lead present. If sufficient scavenger is 
added
to theoretically react with all the lead present, the amount is called 
one
"theory". Typically, 1.0 to 1.5 theories are used, but aviation 
gasolines
must only use one theory. This ensures there is no excess bromine that 
could 
react with the engine. 

The alkyl leads rapidly became the most cost-effective method of 
enhancing 
octane. The introduction was not universally acclaimed, as the toxicity
of TEL soon became apparent, and several eminent public health officials
campaigned against the widespread introduction of alkyl leads [18]. 
Their cause was assisted by some major disasters at TEL manufacturing
plants, and although these incidents were mainly attributable to a 
failure
of management and/or staff to follow instructions, they resulted in a
protracted dispute in the chemical and public health literature that 
even
involved Midgley [18,19]. We should be careful retrospectively
applying judgement to the 1920s, as the increased octane of leaded 
gasoline 
provided major gains in engine efficiency and lower gasoline prices.     

The development of the alkyl leads ( tetra methyl lead, tetra ethyl lead 
) 
and the toxic halogenated scavengers meant that petroleum refiners could 
then configure refineries to produce hydrocarbon  streams that would 
increase octane with small quantities of alkyl lead. If you keep adding 
alkyl lead compounds, the lead response of the gasoline decreases, and 
so 
there are economic limits to how much lead should be added.

Up until the late 1960s, alkyl leads were added to gasolines in 
increasing 
concentrations to obtain octane. The limit was 1.14g Pb/l, which is well 
above the diminishing returns part of the lead response curve for most 
refinery streams, thus it is unlikely that much fuel was ever made at 
that 
level. I believe 1.05 was about the maximum, and articles suggest that 
1970 
100 RON premiums were about 0.7-0.8 g Pb/l and 94 RON regulars 0.6-0.7 g 
Pb/l, which matches published lead response data [20] eg.
         
For             Catalytic Reformate           Straight Run Naphtha.
Lead g/l                    Research Octane Number
   0                   96                           72
  0.1                  98                           79
  0.2                  99                           83
  0.3                 100                           85
  0.4                 101                           87
  0.5                 101.5                         88
  0.6                 102                           89
  0.7                 102.5                         89.5
  0.8                 102.75                        90

The alkyl lead anti-knocks work in a different stage of the pre-
combustion
reaction to oxygenates. In contrast to oxygenates, the alkyl lead 
interferes 
with hydrocarbon chain branching in the intermediate temperature range 
where HO2 is the most important radical species. Lead oxide, either as 
solid particles, or in the gas phase, reacts with HO2 and removes it 
from
the available radical pool, thereby deactivating the major chain 
branching 
reaction sequence that results in undesirable, easily-autoignitable
hydrocarbons [14,15]. 

By the 1960s, the nature the toxicity of the emissions from gasoline-
powered
engines was becoming of increasing concern and extensive comparisons of 
the
costs and benefits were being performed. By the 1970s, the failure to 
find
durable, lead-tolerant exhaust catalysts would hasten the departure of 
lead,
as the proposed regulated emissions levels could not be economically 
achieved without exhaust catalysts [21]. 

4.7  Why not use other organometallic compounds?

As the toxicity of the alkyl lead and the halogenated scavengers became 
of 
concern, alternatives were considered. The most famous of these is 
methylcyclopentadienyl manganese tricarbonyl (MMT), which was used in 
the 
USA until banned by the EPA from 27 Oct 1978 [22], but is approved for 
use 
in Canada and Australia. Recently the EPA ban was overturned, however it 
is
unlikely that MMT will be permitted, mainly because automobile 
manufacturers
believe MMT reduces the effectiveness of the latest emission control 
systems [23]. Canada is also contemplating banning MMT because of the
same concerns, as well as achieving fuel supply uniformity with the 
lower
48 states of the USA [23].  MMT is more expensive than alkyl leads and 
has 
been reported to increase unburned hydrocarbon emissions and block 
exhaust 
catalysts [24]. 

Other compounds that enhance octane have been suggested, but usually 
have 
significant problems such as toxicity, cost, increased engine wear etc.. 
Examples include dicyclopentadienyl iron and nickel carbonyl. Germany 
used 
iron pentacarbonyl Fe(CO)5 at levels of 0.5% or less in gasoline during 
the 
1930s. While its cost was low, one of its drawbacks was that the 
carbonyl 
decomposed rapidly when the gasoline was exposed to light. Fe3O4 also 
deposited on the spark plug insulator causing short circuits, and the 
precipitation of iron oxides in the lubricating oil also led to 
excessive
wear rates [25].

4.8  What do the refining processes do?

Crude oil contains a wide range of hydrocarbons, organometallics and 
other 
compounds containing sulfur, nitrogen etc. The HCs contain between 1 and 
60 
carbon atoms. Gasoline requires hydrocarbons with carbon atoms between 3 
and 
12, arranged in specific ways to provide the desirable properties. 
Obviously, 
a refinery has to either sell the remainder as marketable products, or 
convert the larger molecules into smaller gasoline molecules.

A refinery will distill crude oil into various fractions and, depending 
on 
the desired final products, will further process and blend those 
fractions. 
Typical final products could be:- gases for chemical synthesis and fuel 
(CNG), liquified gases (LPG), butane, aviation and automotive gasolines, 
aviation and lighting kerosines, diesels, distillate and residual fuel 
oils,
lubricating oil base grades, paraffin oils and waxes. Many of the common 
processes are intended to increase the yield of blending feedstocks for 
gasolines. 

Typical modern refinery processes for gasoline components include
* Catalytic cracking - breaks larger, higher-boiling, hydrocarbons into
  gasoline range product that contains 30% aromatics and 20-30% olefins.
* Hydrocracking - cracks and adds hydrogen to molecules, producing a
  more saturated, stable, gasoline fraction.
* Isomerisation - raises gasoline fraction octane by converting straight 
  chain hydrocarbons into branched isomers.
* Reforming - converts saturated, low octane, hydrocarbons into higher 
octane
  product containing about 60% aromatics.
* Alkylation - reacts gaseous olefin streams with isobutane to produce 
liquid
  high octane iso-alkanes.

The changes to the US Clean Air Act and other legislation ensures that 
the 
refineries will continue to modify their processes to produce a less 
volatile gasoline with fewer toxins and toxic emissions. Options 
include:-
* Reducing the "severity" of reforming to reduce aromatic production.   
* Distilling the C5/C6 fraction from reformer feeds and treating that
  stream to produce non-aromatic high octane components.
* Distilling the higher boiling fraction ( which contains 80-100% of 
  aromatics that can be hydrocracked ) from catalytic cracker product 
[26].
* Convert butane to isobutane or isobutylene for alkylation or MTBE 
feed.

Some other countries are removing the alkyl lead compounds for health
reasons, and replacing them with aromatics and oxygenates. If the 
vehicle
fleet does not have exhaust catalysts, the emissions of some toxic
aromatic hydrocarbons can increase. If maximum environmental and health 
gains are to be achieved, the removal of lead from gasoline should be
accompanied by the immediate introduction of exhaust catalysts and
sophisticated engine management systems, 

4.9  What energy is released when gasoline is burned?

It is important to note that the theoretical energy content of gasoline
when burned in air is only related to the hydrogen and carbon contents.
The energy is released when the hydrogen and carbon are oxidised 
(burnt),
to form water and carbon dioxide. Octane rating is not fundamentally 
related to the energy content, and the actual hydrocarbon and oxygenate 
components used in the gasoline will determine both the energy release 
and 
the anti-knock rating.

Two important reactions are:-
          C + O2 = CO2
          H + O2 = H2O   
The mass or volume of air required to provide sufficient oxygen to 
achieve 
this complete combustion is the "stoichiometric" mass or volume of air.
Insufficient air = "rich", and excess air = "lean", and the 
stoichiometric
mass of air is related to the carbon:hydrogen ratio of the fuel. The
procedures for calculation of stoichiometric air/fuel ratios are fully
documented in an SAE standard [27]. 

Atomic masses used are:- Hydrogen = 1.00794, Carbon = 12.011, 
Oxygen = 15.994, Nitrogen = 14.0067, and Sulfur = 32.066.

The composition of sea level air ( 1976 data, hence low CO2 value ) is
Gas            Fractional      Molecular Weight         Relative 
Species          Volume            kg/mole                Mass
N2              0.78084             28.0134             21.873983
O2              0.209476            31.9988              6.702981
Ar              0.00934             39.948               0.373114
CO2             0.000314            44.0098              0.013919
Ne              0.00001818          20.179               0.000365
He              0.00000524           4.002602            0.000021
Kr              0.00000114          83.80                0.000092
Xe              0.000000087        131.29                0.000011
CH4             0.000002            16.04276             0.000032
H2              0.0000005            2.01588             0.000001
                                                        ---------
Air                                                     28.964419  

For normal heptane C7H16 with a molecular weight = 100.204 
           C7H16 + 11O2 = 7CO2 + 8H2O
thus 1.000 kg of C7H16 required 3.513 kg of O2 = 15.179 kg air.

The chemical stoichiometric combustion of hydrocarbons with oxygen can 
be 
written as:-
CxHy + (x + (y/4))O2  ->  xCO2 + (y/2)H2O
Often, for simplicity, the remainder of air is assumed to be nitrogen, 
which can be added to the equation when exhaust compositions are 
required.
As a general rule, maximum power is achieved at slightly rich, whereas
maximum fuel economy is achieved at slightly lean. 

The energy content of the gasoline is obtained by burning all the fuel 
inside a bomb calorimeter and measuring the temperature increase. 
The energy available depends on what happens to the water produced from 
the 
combustion of the hydrogen. If the water remains as a gas, then it 
cannot 
release the heat of vaporisation, thus producing the Nett Calorific 
Value. 
If the water were condensed back to the original fuel temperature, then 
Gross Calorific Value of the fuel, which will be larger, is obtained.

The calorific values are fairly constant for families of HCs, which is 
not 
surprising, given their fairly consistent carbon/hydrogen ratios. For 
liquid 
( l ) or gaseous ( g ) fuel converted to gaseous products - except for 
the 
2-methylbutene-2, where only gaseous is reported. * = Blending Octane 
Number
Typical Heats of Combustion are [28]:-

Fuel     State  Heat of Combustion      Research        Motor
                    MJ/kg                Octane         Octane 
n-heptane  l        44.592                  0              0
           g        44.955
i-octane   l        44.374                100            100
           g        44.682
toluene    l        40.554                124*           112*
           g        40.967
2-methylbutene-2    44.720                176*           141*
  
Because all the data is available, the calorific value of fuels can be 
estimated quite accurately from hydrocarbon fuel properties such as the 
density, sulfur content, and aniline point ( which indicates the 
aromatics 
content ).

It should be noted that because oxygenates contain oxygen that can
not provide energy, they will have significantly lower energy contents.
They are added to provide octane, not energy. For an engine that can be
optimised for oxygenates, more fuel is required to obtain the same 
power,
but they can burn slightly more efficiently, thus the power ratio is not 
identical to the energy content ratio. They also require more energy to
vaporise.
            Energy Content   Heat of Vaporisation   Oxygen Content    
              Nett MJ/kg          MJ/kg                   wt%

_
                                                              

Methanol        19.95             1.154                  49.9
Ethanol         26.68             0.913                  34.7
MTBE            35.18             0.322                  18.2
ETBE            36.29             0.310                  15.7
TAME            36.28             0.323                  15.7
Gasoline       42 - 44            0.297                   0.0

Typical values for commercial fuels in megajoules/kilogram are [29]:- 
                                Gross        Nett      
Hydrogen                        141.9       120.0
Carbon to Carbon monoxide        10.2          -
Carbon to Carbon dioxide         32.8          -
Sulfur to sulfur dioxide          9.16         -
Natural Gas                      53.1         48.0
Liquified petroleum gas          49.8         46.1
Aviation gasoline                46.0         44.0
Automotive gasoline              45.8         43.8
Kerosine                         46.3         43.3
Diesel                           45.3         42.5
     
Obviously, for automobiles, the nett calorific value is appropriate, as 
the
water is emitted as vapour. The engine can not utilise the additional 
energy 
available when the steam is condensed back to water. The calorific value 
is 
the maximum energy that can be obtained from the fuel by combustion, but 
the 
reality of modern SI engines is that efficiencies of only 20-40% may be 
obtained, this limit being due to engineering and material constraints 
that prevent optimum combustion conditions being used. The CI engine can 
achieve higher efficiencies, usually over a wider operating range as 
well.    


4.10  What are the gasoline specifications?

Gasolines are usually defined by government regulation, where properties 
and
test methods are clearly defined. In the US, several government and 
state
bodies can specify gasoline properties. The US gasoline specifications 
and 
test methods are listed in several readily available publications, 
including
the Society of Automotive Engineers (SAE) [30], and the American Society 
for
Testing Materials (ASTM) [31]. The 1995 ASTM edition has:-

D4814-94d Specification for Automotive Spark-Ignition Engine Fuel.

This specification lists various properties that all fuels have to 
comply 
with, and may be updated throughout the year. Typical properties are:- 

4.10.1 Vapour Pressure and Distillation Classes. 
6 different classes according to location and/or season.
As gasoline is distilled, the temperatures at which various fractions 
are
evaporated are calculated. Specifications define the temperatures at 
which
various percentages of the fuel are evaporated. Distillation limits 
include maximum temperatures that 10% is evaporated (50-70C), 50% is 
evaporated (110-121C), 90% is evaporated (185-190C), and the final 
boiling 
point (225C). A minimum temperature for 50% evaporated (77C), and a 
maximum 
amount of Residue (2%) after distillation.  Vapour pressure limits for
each class ( 54, 62, 69, 79, 93, 103 kPa ) are also specified. Note that 
the 
EPA has issued a waiver that does not require gasoline/ethanol blends to
meet the required specifications.

4.10.2 Vapour Lock Protection Classes
5 classes for vapour lock protection, according to location and/or 
season.
The limit is a maximum Vapour/Liquid ratio of 20 at test temperatures of 
41, 47, 51, 56, 60C.
   
4.10.3 Antiknock Index   ( aka (RON+MON)/2, "Pump Octane" )
The ( Research Octane Number + Motor Octane Number ) divided by two. 
Limits 
are not specified, but changes in engine requirements according season 
and 
location are discussed. Fuels with an Antiknock index of 87, 89, 91 
( Unleaded), and 88 ( Leaded ) are listed as typical for the US.

4.10.4 Lead Content
Leaded = 1.1 g Pb / L maximum, and Unleaded = 0.013 g Pb / L maximum.
  
4.10.5 Copper strip corrosion
Ability to tarnish clean copper, indicating the presence of any 
corrosive 
sulfur compounds 

4.10.6 Maximum Sulfur content
Sulfur adversely affects exhaust catalysts and fuel hydrocarbon lead 
response, and also may be emitted as polluting sulfur oxides.
Leaded = 0.15 %mass maximum, and Unleaded = 0.10 %mass maximum.
Typical US gasoline levels are 0.03 %mass.  

4.10.7 Maximum Existent Gum   
Limits the amount of gums present in fuel at the time of testing to
5 mg/100mls. The results do not correlate well with actual engine 
deposits 
caused by fuel vaporisation [32].

4.10.8 Minimum Oxidation Stability
This ensures the fuel remains chemically stable, and does not form 
additional 
gums during periods in distribution systems, which can be up to 3-6 
months. 
The sample is heated with oxygen inside a pressure vessel, and the delay 
until significant oxygen uptake is measured. 
 
4.10.9 Water Tolerance
Highest temperature that causes phase separation of oxygenated fuels.
The limits vary according to location and month. For Alaska - North of 
62 
latitude, it changes from -41C in Dec/Jan to 9C in July, but remains 10C 
all 
year in Hawaii.

Because phosphorus adversely affects exhaust catalysts, the EPA limits 
phosphorus in all gasolines to 0.0013g P/L.

As well as the above, there are various restrictions introduced by the 
Clean 
Air Act and state bodies such as California's Air Resources Board (CARB) 
that 
often have more stringent limits for the above properties, as well as 
additional limits. The Clean Air Act also specifies some regions that 
exceed 
air quality standards have to use reformulated gasolines (RFGs) all 
year, 
starting January 1995. Other regions are required to use oxygenated 
gasolines for four winter months, beginning November 1992. The RFGs also 
contain oxygenates. Metropolitan regions with severe ozone air quality 
problems must use reformulated gasolines in 1995 that;- contain at least 
2.0 wt% oxygen, reduce 1990 volatile organic carbon compounds by 15%, 
and 
reduce specified toxic emissions by 15% (1995) and 25% (2000). 
Metropolitan 
regions that exceeded carbon monoxide limits were required to use 
gasolines 
with 2.7 wt% oxygen during winter months, starting in 1992. 

The 1990 Clean Air Act (CAA) amendments and CARB phase 2 (1996) 
specifications for reformulated gasoline establish the following limits, 
compared with typical 1990 gasoline. Because of a lack of data, the EPA
were unable to define the CAA required parameters , so they instituted
a two-stage system. The first stage, the "Simple Model" is an interim
stage that run from 1/Jan/1995 to 1/May/1997. The second stage, the 
"Complex Model" would be developed, with the following parameters likely
to be controlled - reid vapour pressure, benzene, oxygen, sulfur, 
olefins
distillation ( 90% Evaporated ), and aromatics. Each refiner must have
their RFG recertified using the Complex model by 1/May/1997 [33]. 
 
                       1990           Clean Air Act       CARB
benzene                 2 %              1 % maximum      1.0 vol% 
maximum
oxygen                  0.2 %            2 % minimum    1.8-2.0 mass%
sulfur                150 ppm            no increase     40 ppm
aromatics              32.0 %           25 % maximum     25 vol% maximum
olefins                 9.9 %            5 % maximum      6 vol% maximum
reid vapour pressure   60 kPa           56 kPa (north)   48 kPa
                                        50 kPa (south)
90% evaporated        170 C              -              149 C

These regulations also specify emissions criteria. eg CAA specifies no 
increase in nitric oxides (NOx) emissions, reductions in VOC by 15% 
during 
the ozone season, and specified toxins by 15% all year. These criteria
indirectly establish vapour pressure and composition limits that 
refiners
have to meet. Note that the EPA also can issue CAA Section 211 waivers 
that 
allow refiners to choose which oxygenates they use. In 1981, the EPA 
also 
decided that fuels with up to 2% alcohols and ethers (except methanol) 
were 
"substantially similar" to 1974 unleaded gasoline, and thus were not 
"new"
gasoline additives. That level was increased to 2.7 wt% in 1991. Some 
other
oxygenates have also been granted waivers, eg ethanol to 3.5 wt% in 
1979/1982, and tert-butyl alcohol to 3.5 wt% in 1981. 

4.11 What are the effects of the specified fuel properties? 

Volatility 
This affects evaporative emissions and driveability, it is the property 
that
must change with location and season. Fuel for mid-summer Arizona would 
be 
difficult to use in mid-winter Alaska. The US is divided into zones, 
according to altitude and seasonal temperatures, and the fuel volatility 
is 
adjusted accordingly. Incorrect fuel may result in difficult starting in 
cold weather, carburetter icing, vapour lock in hot weather, and 
crankcase 
oil dilution. Volatility is controlled by distillation and vapour 
pressure 
specifications. The higher boiling fractions of the gasoline have 
significant
effects on the emission levels of undesirable hydrocarbons and 
aldehydes, 
and a reduction of 40C in the final boiling point will reduce the levels 
of
benzene, butadiene, formaldehyde and acetaldehyde by 25%, and will 
reduce
HC emissions by 20% [34].

Combustion Characteristics
As gasolines contain mainly hydrocarbons, the only significant variable 
between different grades is the octane rating of the fuel, as most other 
properties are similar. Octane is discussed in detail in Section 6. 
There
are only slight differences in combustion temperatures ( most are around
2000C in isobaric adiabatic combustion [35]). Note that the actual 
temperature in the combustion chamber is also determined by other 
factors, 
such as load and engine design. The addition of oxygenates changes the 
pre-flame reaction pathways, and also reduces the energy content of the 
fuel. 
The levels of oxygen in the fuel is regulated according to regional air 
quality standards.

Stability
Motor gasolines may be stored up to six months, consequently they must 
not 
form gums which may precipitate. Gums are usually the result of 
copper-catalysed reactions of the unsaturated HCs, so antioxidants and 
metal 
deactivators are added. Existent Gum is used to measure the gum in the 
fuel 
at the time tested, whereas the Oxidation Stability measures the time it 
takes for the gasoline to break down at 100C with 100psi of oxygen. A 
240 
minute test period has been found to be sufficient for most storage and 
distribution systems.

Corrosiveness
Sulfur in the fuel creates corrosion, and when combusted will form 
corrosive
gases that attack the engine, exhaust and environment. Sulfur also 
adversely
affects the alkyl lead octane response and may poison exhaust catalysts. 
The 
copper strip corrosion test and the sulfur specification are used to 
ensure 
fuel quality. The copper strip test measures active sulfur, whereas the 
sulfur content reports the total sulfur present.

4.12 Are brands different?

Yes. The above specifications are intended to ensure minimal quality 
standards are maintained, however as well as the fuel hydrocarbons, the 
manufacturers add their own special ingredients to provide additional 
benefits. A quality gasoline additive package would include:-
* octane-enhancing additives ( improve octane ratings )  
* anti-oxidants ( inhibit gum formation, improve stability ) 
* metal deactivators ( inhibit gum formation, improve stability )
* deposit modifiers ( reduce deposits, spark-plug fouling and 
  preignition )
* surfactants ( prevent icing, improve vaporisation, inhibit deposits,
  reduce NOx emissions ) 
* freezing point depressants ( prevent icing )
* corrosion inhibitors ( prevent gasoline corroding storage tanks ) 
* dyes ( product colour for safety or regulatory purposes ).
 
During the 1980s significant problems with deposits accumulating on 
intake 
valve surfaces occurred as new fuel injections systems were introduced. 
These intake valve deposits (IVD) were different than the injector 
deposits,
in part because the valve can reach 300C. Engine design changes that 
prevent 
deposits usually consist of ensuring the valve is flushed with liquid 
gasoline, and provision of adequate valve rotation. Gasoline factors 
that 
cause deposits are the presence of alcohols or olefins [36]. Gasoline 
manufacturers now routinely use additives that prevent IVD and also 
maintain 
the cleanliness of injectors. These usually include a surfactant and 
light 
oil to maintain the wetting of important surfaces. Intake valve deposits 
have 
also been shown to have significant adverse effects on emissions [37].
A more detailed description of additives is provided in Section 9.1.

Texaco demonstrated that a well-formulated package could improve fuel 
economy, reduce NOx emissions, and restore engine performance because, 
as 
well as the traditional liquid-phase deposit removal, some additives can 
work in the vapour phase to remove existing engine deposits without
adversely affecting performance ( as happens when water is poured into a 
running engine to remove carbon deposits:-) )[38]. Chevron have also
published data on the effectiveness of their additives [39]. Most 
suppliers of quality gasolines will formulate similar additives into 
their 
products, and cheaper lines are less like to have such additives added. 
As different brands use different additives and oxygenates, it is 
probable 
that important fuel parameters, such as octane distribution, are 
different, 
even though the pump octane ratings are the same. 

So, if you know your car is well-tuned, and in good condition, but the
driveability is pathetic on the correct octane, try another brand. 
Remember 
that the composition will change with the season, so if you lose 
driveability, try yet another brand. As various Clean Air Act changes 
are 
introduced over the next few years, gasoline will continue to change.




                                                                                                                 

ac.nz
zephyr.grace.cri.nz!usenet



Archive-name: autos/gasoline-faq/part2

4.13 What is a typical composition?

There seems to be a perception that all gasolines of one octane grade 
are
chemically similar, and thus general rules can be promulgated about 
"energy 
content ", "flame speed", "combustion temperature" etc. etc.. Nothing is 
further from the truth. The behaviour of manufactured gasolines in 
octane 
rating engines can be predicted, using previous octane ratings of 
special
blends intended to determine how a particular refinery stream responds 
to 
an octane-enhancing additive. Refiners can design and reconfigure 
refineries 
to efficiently produce a wide range of gasolines feedstocks, depending 
on
market and regulatory requirements. There is a worldwide trend to move 
to
unleaded gasolines, followed by the introduction of exhaust catalysts 
and 
sophisticated engine management systems. 

It is important to note that "oxygenated gasolines" have a hydrocarbon
fraction that is not too different to traditional gasolines, but that 
the
hydrocarbon fraction of "reformulated gasolines" ( which also contain 
oxygenates ) are significantly different to traditional gasolines.

The last 10 years of various compositional changes to gasolines for
environmental and health reasons have resulted in fuels that do not 
follow 
historical rules, and the regulations mapped out for the next decade 
also 
ensure the composition will remain in a state of flux. The reformulated
gasoline specifications, especially the 1/May/1997 Complex model, will
probably introduce major reductions in the distillation range, as well 
as
the various limits on composition and emissions.

I'm not going to list all 500+ HCs in gasolines, but the following are 
representative of the various classes typically present in a gasoline. 
The 
numbers after each chemical are:- Research Blending Octane : Motor 
Blending 
Octane : Boiling Point (C): Density (g/ml @ 15C) : Minimum Autoignition 
Temperature (C). It is important to realise that the Blending Octanes 
are 
derived from a 20% mix of the HC with a 60:40 iC8:nC7 base, and the 
extrapolation of this 20% to 100%. This is different from rating the 
pure 
fuel, which often requires adjustment of the test engine conditions 
outside 
the acceptable limits of the rating methods. Generally the actual 
octanes of 
the pure fuel are similar for the alkanes, but are up to 30 octane 
numbers 
lower than the blending octanes for the aromatics and olefins [40].   

A traditional composition I have dreamed up would be like the following, 
whereas newer oxygenated fuels reduce the aromatics and olefins, narrow 
the
boiling range, and add oxygenates up to about 12-15% to provide the 
octane.
The amount of aromatics in super unleaded fuels will vary greatly from
country to country, depending on the configuration of the oil refineries 
and the use of oxygenates as octane enhancers. The US is reducing the 
levels 
of aromatics to 25% or lower for environmental and human health reasons.

Some countries are increasing the level of aromatics to 50% or higher in 
super unleaded grades, usually to avoid refinery reconfiguration costs 
or
the introduction of oxygenates as they phase out the toxic lead octane
enhancers. An upper limit is usually placed on the amount of benzene
permitted, as it is known human carcinogen.

15% n-paraffins                       RON   MON    BP      d     AIT  
        n-butane                      113 : 114 :  -0.5:  gas  : 370
        n-pentane                      62 :  66 :  35  : 0.626 : 260
        n-hexane                       19 :  22 :  69  : 0.659 : 225
        n-heptane (0:0 by definition)   0 :   0 :  98  : 0.684 : 225
        n-octane                      -18 : -16 : 126  : 0.703 : 220
     ( you would not want to have the following alkanes in gasoline, 
       so you would never blend kerosine with gasoline )
        n-decane                      -41 : -38 : 174  : 0.730 : 210
        n-dodecane                    -88 : -90 : 216  : 0.750 : 204
        n-tetradecane                 -90 : -99 : 253  : 0.763 : 200
30%  iso-paraffins  
        2-methylpropane               122 : 120 : -12  :  gas  : 460
        2-methylbutane                100 : 104 :  28  : 0.620 : 420
        2-methylpentane                82 :  78 :  62  : 0.653 : 306
        3-methylpentane                86 :  80 :  64  : 0.664 :  -
        2-methylhexane                 40 :  42 :  90  : 0.679 : 
        3-methylhexane                 56 :  57 :  91  : 0.687 :
        2,2-dimethylpentane            89 :  93 :  79  : 0.674 :
        2,2,3-trimethylbutane         112 : 112 :  81  : 0.690 : 420
        2,2,4-trimethylpentane        100 : 100 :  98  : 0.692 : 415
          ( 100:100 by definition )
12% cycloparaffins 
        cyclopentane                  141 : 141 :  50  : 0.751 : 380
        methylcyclopentane            107 :  99 :  72  : 0.749 : 
        cyclohexane                   110 :  97 :  81  : 0.779 : 245
        methylcyclohexane             104 :  84 : 101  : 0.770 : 250
35% aromatics        
        benzene                        98 :  91 :  80  : 0.874 : 560
        toluene                       124 : 112 : 111  : 0.867 : 480
        ethyl benzene                 124 : 107 : 136  : 0.867 : 430
        meta-xylene                   162 : 124 : 138  : 0.868 : 463
        para-xylene                   155 : 126 : 138  : 0.866 : 530
        ortho-xylene                  126 : 102 : 144  : 0.870 : 530
        3-ethyltoluene                162 : 138 : 158  : 0.865 : 
        1,3,5-trimethylbenzene        170 : 136 : 163  : 0.864 : 
        1,2,4-trimethylbenzene        148 : 124 : 168  : 0.889 :
8% olefins               
        2-pentene                     154 : 138 :  37  : 0.649 :
        2-methylbutene-2              176 : 140 :  36  : 0.662 :
        2-methylpentene-2             159 : 148 :  67  : 0.690 :
        cyclopentene                  171 : 126 :  44  : 0.774 :
    ( the following olefins are not present in significant amounts
      in gasoline, but have some of the highest blending octanes )   
        1-methylcyclopentene          184 : 146 :  75  : 0.780 :
        1,3 cyclopentadiene           218 : 149 :  42  : 0.805 :
        dicyclopentadiene             229 : 167 : 170  : 1.071 :     

Oxygenates 
Published octane values vary a lot because the rating conditions are 
significantly different to standard conditions, for example the API 
Project 
45 numbers used above for the hydrocarbons, reported in 1957, gave MTBE 
blending RON as 148 and MON as 146, however that was based on the lead 
response, whereas today we use MTBE in place of lead.
  
        methanol                      133 : 105 :  65  : 0.796 : 385
        ethanol                       129 : 102 :  78  : 0.794 : 365
        iso propyl alcohol            118 :  98 :  82  : 0.790 : 399
        methyl tertiary butyl ether   116 : 103 :  55  : 0.745 : 
        ethyl tertiary butyl ether    118 : 102 :  72  : 0.745 :
        tertiary amyl methyl ether    111 :  98 :  86  : 0.776 : 
        
There are some other properties of oxygenates that have to be considered
when they are going to be used as fuels, particularly their ability to
form very volatile azeotropes that cause the fuel's vapour pressure to
increase, the chemical nature of the emissions, and their tendency to 
separate into a separate water/oxygenate phase when water is present. 
The reformulated gasolines address these problems more successfully than 
the original oxygenated gasolines.

Before you rush out to make a highly aromatic or olefinic gasoline to 
produce a high octane fuel, remember they have other adverse properties, 
eg the aromatics attack elastomers, may generate smoke, and result in
increased emissions of toxic benzene. The olefins are unstable ( besides 
smelling foul ) and form gums. The art of correctly formulating a 
gasoline 
that does not cause engines to knock apart, does not cause vapour lock 
in 
summer - but is easy to start in winter, does not form gums and 
deposits, 
burns cleanly without soot/residues, and does not dissolve or poison the 
car catalyst or owner, is based on knowledge of the gasoline 
composition.

4.14 Is gasoline toxic or carcinogenic? 

There are several known toxins in gasoline, some of which are confirmed
human carcinogens. The most famous of these toxins are lead and benzene, 
and 
both are regulated. The other aromatics and some toxic olefins are also 
controlled. Lead alkyls also require ethylene dibromide and/or ethylene 
dichloride scavengers to be added to the gasoline, both of which are 
suspected human carcinogens. In 1993 an International Symposium on the 
Health
Effects of Gasoline was held [41]. Major review papers on the 
carcinogenic,
neurotoxic, reproductive and developmental toxicity of gasoline, 
additives,
and oxygenates were presented, and interested readers should obtain the
proceedings. The oxygenates are also being evaluated for 
carcinogenicity, and 
even ethanol and ETBE may be carcinogens. The introduction of oxygenated
gasoline to Alaska and some other areas of the USA resulted in a range 
of
complaints. Recent research has been unable to identify additional 
toxicity,
but has detected increased levels of offensive smell [42]. It should be 
noted 
that the oxygenated gasolines were not initially intended to reduce the 
toxicity of emissions. The reformulated gasolines will produce different 
emissions, and specific toxins must initially be reduced by 15% all 
year.

The removal of alkyl lead compounds certainly reduces the toxicity of 
exhaust gas emissions when used on engines with modern engine management
systems and 3-way exhaust catalysts. If unleaded gasolines are not 
accompanied by the introduction of catalysts, some other toxic emissions
may increase. Engines without catalysts will produce increased levels of
toxic carbonyls such as formaldehyde and acrolein when using oxygenated
fuels, and increased levels of toxic benzene when using highly aromatic 
fuels.   

There is little doubt that gasoline is full of toxic chemicals, and 
should
therefore be treated with respect. However the biggest danger remains 
the 
flammability, and the relative hazards should always be kept in 
perspective. 
The major toxic risk from gasolines comes from breathing the tailpipe, 
evaporative, and refuelling emissions, rather than occasional skin 
contact 
from spills. Breathing vapours and skin contact should always be 
minimised.

4.15 Is unleaded gasoline more toxic than leaded?

The short answer is no. However that answer is not global, as some 
countries 
have replaced the lead compound octane-improvers with aromatic or olefin
octane-improvers without introducing exhaust catalysts. The aromatics
contents may increase to around 40%, with high octane unleaded fuels 
reaching 
50% in countries where oxygenates are not being used, and the producers 
have 
not reconfigured refineries to produce high octane paraffins. In 
general, 
aromatics are significantly more toxic than paraffins. Exhaust catalysts  
have a limited operational life, and will be immediately poisoned if 
misfuelled with leaded fuel. Catalyst failure can result in higher 
levels of
toxic emissions if catalysts or engine management systems are not 
replaced or
repaired when defective. Maximum benefit of the switch to unleaded are
obtained when the introduction of unleaded is accompanied by the 
introduction
of exhaust catalysts and sophisticated engine management systems.

Unfortunately, the manufacturers of alkyl lead compounds have embarked 
on a 
worldwide misinformation campaign in countries considering emulating the 
lead-free US. The use of lead precludes the use of exhaust catalysts, 
thus 
the emissions of aromatics are only slightly diminished, as leaded fuels
typically contain around 30-40% aromatics. Other toxins and pollutants 
that 
are usually reduced by exhaust catalysts will be emitted at 
significantly 
higher levels if leaded fuels are used [43]. 

The use of unleaded on modern vehicles with engine management systems 
and 
catalysts can reduce aromatic emissions to 10% of the level of vehicles 
without catalysts [43]. Alkyl lead additives can only substitute for 
some of 
the aromatics in gasoline, consequently they do not eliminate aromatics,
which will produce benzene emissions [44]. Alkyl lead additives also 
require 
toxic organohalogen scavengers, which also react in the engine to form 
and 
emit other organohalogens, including highly toxic dioxin [45]. Leaded 
fuels 
emit lead, organohalogens, and much higher levels of regulated toxins 
because they preclude the use of exhaust catalysts. In the USA the 
gasoline
composition is being changed to reduce fuel toxins ( olefins, aromatics 
) 
as well as emissions of specific toxins. 

4.16 Is reformulated gasoline more toxic than unleaded?

The evidence so far indicates that the components of reformulated 
gasolines
( RFGs ) are more benign than unleaded, and that the tailpipe emissions 
of 
hydrocarbons are significantly reduced for cars without catalysts, and 
slightly reduced for cars with catalysts and engine management systems. 
The
emissions of toxic carbonyls such as formaldehyde, acetaldehyde and 
acrolein 
are increased slightly on all vehicles, and the emission of MTBE is 
increased
about 10x on cars without catalysts and 4x on cars with catalysts [43].
When all the emissions ( evaporative and tailpipe ) are considered, RFGs
significantly reduce emissions of hydrocarbons, however the emissions of
carbonyls and MTBE may increase [43]. More research is required before a
definitive answer on toxicity is available.  

The major question about RFGs is not the toxicity of the emissions, but 
whether they actually meet their objective of reducing urban pollution.
This is a more complex issue, and most experts agree the benefits will 
only
be modest [46]. 

4.17 Are all oxygenated gasolines also reformulated gasolines?

No. Oxygenates were initially introduced as alternative octane-enhancers 
in 
the 1930s, and are still used in some countries for that purpose. 
In the US the original "oxygenated gasolines" usually had a slightly-
modified gasoline as the hydrocarbon fraction. The US EPA also mandated 
their use to reduce pollution, mainly via the "enleanment" effect on 
engines 
without sophisticated management systems, but also because of the 
"aromatics 
substitution" effect. As vehicles with fuel injection and sophisticated 
engine management systems became pervasive, reformulated gasolines could 
be 
introduced to further reduce pollution. The hydrocarbon component of 
RFGs is 
significantly different to the hydrocarbon fraction in earlier 
oxygenated 
gasolines, having lower aromatics contents, reduced vapour pressure, and 
a 
narrower boiling range. RFGs do contain oxygenates as the octane-
enhancer, 
but have different hydrocarbon composition profiles [26,33,34,39,43].

------------------------------


5.1  Why pick on cars and gasoline? 

Cars emit several pollutants as combustion products out the tailpipe,
(tailpipe emissions), and as losses due to evaporation (evaporative 
emissions, refuelling emissions). The volatile organic carbon (VOC) 
emissions from these sources, along with nitrogen oxides (NOx) emissions 
from the tailpipe, will react in the presence of ultraviolet (UV) light
(wavelengths of less than 430nm) to form ground-level (tropospheric) 
ozone, 
which is one of the major components of photochemical smog [47]. Smog 
has 
been a major pollution problem ever since coal-fired power stations were 
developed in urban areas, but their emissions are being cleaned up. Now 
it's 
the turn of the automobile.

Cars currently use gasoline that is derived from fossil fuels, thus when 
gasoline is burned to completion, it produces additional CO2 that is 
added 
to the atmospheric burden. The effect of the additional CO2 on the 
global 
environment is not known, but the quantity of man-made emissions of 
fossil 
fuels must cause the system to move to a new equilibrium. Even if 
current 
research doubles the efficiency of the IC engine/gasoline combination, 
and 
reduces HC, CO, NOx, SOx, VOCs, particulates, and carbonyls, the amount 
of 
carbon dioxide from the use of fossil fuels may still cause global 
warming. 
More and more scientific evidence is accumulating that warming is 
occurring 
[48,49]. The issue is whether it is natural, or induced by human 
activities
and and a large panel of scientific experts continues to review 
scientific 
data and models. Interested reader should seek out the various 
publications
of the Intergovernmental Panel on Climate Change (IPCC). There are 
international agreements to limit CO2 emissions to 1990 levels, a target 
that 
will require more efficient, lighter, or appropriately-sized vehicles, - 
if 
we are to maintain the current usage. One option is to use "renewable" 
fuels 
in place of fossil fuels. Consider the amount of energy-related CO2 
emissions 
for selected countries in 1990 [50].

                              CO2 Emissions
                         ( tonnes/year/person )
USA                               20.0
Canada                            16.4
Australia                         15.9
Germany                           10.4
United Kingdom                     8.6
Japan                              7.7
New Zealand                        7.6 
             
The number of new vehicles provides an indication of the magnitude of 
the
problem. Although vehicle engines are becoming more efficient, the 
distance
travelled is increasing, resulting in a gradual increase of gasoline 
consumption. The world production of vehicles (in thousands) over the 
last 
few years was [51];-

Cars

Region                       1990      1991     1992     1993     1994


Africa                        222       213      194      201      209
Asia-Pacific               12,064    12,112   11,869   11,463   11,020
Central & South America       800       888    1,158    1,523    1,727
Eastern Europe              2,466       984    1,726    1,837    1,547
Middle East                    35        24      300      390      274
North America               7,762     7,230    7,470    8,172    8,661
Western Europe             13,688    13,286   13,097   11,141   12,851
Total World                37,039    34,739   35,815   34,721   36,289

Trucks ( including heavy trucks and buses )

Region                       1990      1991     1992     1993     1994


Africa                        133       123      108      101      116
Asia-Pacific                5,101     5,074    5,117    5,057    5,407
Central & South America       312       327      351      431      457
Eastern Europe                980       776      710      600      244
Middle East                    36        28      100      128       76
North America               4,851     4,554    5,371    6,037    7,040
Western Europe              1,924     1,818    1,869    1,718    2,116
Total World                13,336    12,701   13,627   14,073   15,457

To fuel all operating vehicles, considerable quantities of gasoline

_
                                                                                                                

and diesel have to be consumed. Major consumption in 1993 of gasoline 
and middle distillates ( which may include some heating fuels, but
not fuel oils ) in million tonnes.

                             Gasoline    Middle Distillates
USA                           335.6            233.9
Canada                         25.0             24.4
Western Europe                166.0            264.0
Japan                          56.4             89.6
Total World                   802.0            989.0

The USA consumption of gasoline increased from 294.4 (1982) to 335.6 
(1989)
then dipped to 324.2 (1991), and has continued to rise since then to 
reach 
335.6 million tonnes in 1993. In 1993 the total world production of 
crude oil
was 3164.8 million tonnes, of which the USA consumed 787.5 million 
tonnes 
[52]. Transport is a very significant user of crude oil products, thus 
improving the efficiency of utilisation, and minimising pollution from 
vehicles, can produce immediate reductions in emissions of CO2, HCs, 
VOCs, 
CO, NOx, carbonyls, and other chemicals. 

5.2  Why are there seasonal changes?

Only gaseous hydrocarbons burn, consequently if the air is cold, then 
the 
fuel has to be very volatile. But when summer comes, a volatile fuel can 
boil and cause vapour lock, as well as producing high levels of 
evaporative 
emissions. The solution was to adjust the volatility of the fuel 
according 
to altitude and ambient temperature. This volatility change has been 
automatically performed for decades by the oil companies without 
informing 
the public of the changes. It is one reason why storage of gasoline 
through 
seasons is not a good idea. Gasoline volatility is being reduced as 
modern 
engines, with their fuel injection and management systems, can 
automatically 
compensate for some of the changes in ambient conditions - such as 
altitude 
and air temperature, resulting in acceptable driveability using less 
volatile
fuel.

5.3  Why were alkyl lead compounds removed?

" With the exception of one premium gasoline marketed on the east coast
and southern areas of the US, all automotive gasolines from the mid-
1920s
until 1970 contained lead antiknock compounds to increase antiknock 
quality. 
Because lead antiknock compounds were found to be detrimental to the 
performance of catalytic emission control system then under development, 
U.S. passenger car manufacturers in 1971 began to build engines designed 
to 
operate satisfactorily on gasolines of nominal 91 Research Octane 
Number. 
Some of these engines were designed to operate on unleaded fuel while 
others
required leaded fuel or the occasional use of leaded fuel. The 91 RON 
was 
chosen in the belief that unleaded gasoline at this level could be made 
available in quantities required using then current refinery processing
equipment. Accordingly, unleaded and low-lead gasolines were introduced 
during 1970 to supplement the conventional gasolines already available.

Beginning with the 1975 model year, most new car models were equipped
with catalytic exhaust treatment devices as one means of compliance with
the 1975 legal restrictions in the U.S. on automobile emissions. The 
need
for gasolines that would not adversely affect such catalytic devices has 
led to the large scale availability and growing use of unleaded 
gasolines,
with all late-model cars requiring unleaded gasoline."[53].

There was a further reason why alkyl lead compounds were subsequently 
reduced, and that was the growing recognition of the highly toxic nature 
of 
the emissions from a leaded-gasoline fuelled engine. Not only were toxic 
lead emissions produced, but the added toxic lead scavengers ( ethylene 
dibromide and ethylene dichloride ) could react with hydrocarbons to 
produce 
highly toxic organohalogen emissions such as dioxin. Even if catalysts 
were 
removed, or lead-tolerant catalysts discovered, alkyl lead compounds 
would 
remain banned because of their toxicity and toxic emissions [54,55].

5.4  Why are evaporative emissions a problem?

As tailpipe emissions are reduced due to improved exhaust emission 
control 
systems, the hydrocarbons produced by evaporation of the gasoline during 
distribution, vehicle refuelling, and from the vehicle, become more and
more significant. A recent European study found that 40% of man-made 
volatile organic compounds came from vehicles [56]. Many of the problem 
hydrocarbons are the aromatics and olefins that have relatively high 
octane 
values. Any sensible strategy to reduce smog and toxic emissions will 
attack 
evaporative and tailpipe emissions. 

The health risks to service station workers, who are continuously 
exposed 
to refuelling emissions remain a concern [57]. Vehicles will soon be 
required to trap the refuelling emissions in larger carbon canisters, as 
well as the normal evaporative emissions that they already capture. This 
recent decision went in favour of the oil companies, who were opposed by 
the 
auto companies. The automobile manufacturers felt the service station 
should trap the emissions. The activated carbon canisters adsorb organic
vapours, and these are subsequently desorbed from the canister and burnt 
in 
the engine during normal operation, once certain vehicle speeds and 
coolant
temperatures are reached. A few activated carbons used in older vehicles
do not function efficiently with oxygenates.
   
5.5  Why control tailpipe emissions?

Tailpipe emissions were responsible for the majority of pollutants in 
the 
late 1960s after the crankcase emissions had been controlled. Ozone 
levels 
in the Los Angeles basin reached 450-500ppb in the early 1970s, well 
above 
the typical background of 30-50ppb [58].

Tuning a carburetted engine can only have a marginal effect on pollutant 
levels, and there still had to be some frequent, but long-term, 
assessment 
of the state of tuning. Exhaust catalysts offered a post-engine solution 
that could ensure pollutants were converted to more benign compounds. As 
engine management systems and fuel injection systems have developed, the 
volatility properties of the gasoline have been tuned to minimise
evaporative emissions, and yet maintain low exhaust emissions.
 
The design of the engine can have very significant effects on the type 
and 
quantity of pollutants, eg unburned hydrocarbons in the exhaust 
originate 
mainly from combustion chamber crevices, such as the gap between the 
piston 
and cylinder wall, where the combustion flame can not completely use the 
HCs. 
The type and amount of unburned hydrocarbons are related to the fuel 
composition (volatility, olefins, aromatics, final boiling point), as 
well 
as state of tune, engine condition, and age/condition of the engine
lubricating oil [59]. Particulate emissions, especially the size 
fraction 
smaller than ten micrometres, are a serious health concern. The current 
major source is from compression ignition ( diesel ) engines, and the
modern SI engine system has no problem meeting regulatory requirements. 
 
The ability of reformulated gasolines to actually reduce smog has not 
yet 
been confirmed. The composition changes will reduce some compounds, and 
increase others, making predictions of environmental consequences 
extremely 
difficult. Planned future changes, such as the CAA 1997 Complex model 
specifications, that are based on several major ongoing 
government/industry 
gasoline and emission research programmes, are more likely to provide 
unambiguous environmental improvements. One of the major problems is the
nature of the ozone-forming reactions, which require several components 
( VOC, NOx, UV ) to be present. Vehicles can produce the first two, but 
the
their ratio is important, and can be affected by production from other 
natural ( VOC = terpenes from conifers ) or manmade ( NOx from power 
stations ) sources [46,47].  The rules for tailpipe emissions 
will continue to become more stringent as countries try to minimise 
local 
problems ( smog, toxins etc.) and global problems ( CO2 ). Reformulation 
does not always lower all emissions, as evidenced by the following 
aldehydes 
from an engine with an adaptive learning management system [43].
 
                           FTP-weighted emission rates (mg/mi)
                                Gasoline      Reformulated
Formaldehyde                      4.87           8.43
Acetaldehyde                      3.07           4.71

The type of exhaust catalyst and management system can have significant
effects on the emissions  [43].

                           FTP-weighted emission rates. (mg/mi)
                         Total Aromatics          Total Carbonyls
                     Gasoline  Reformulated    Gasoline  Reformulated
Noncatalyst          1292.45     1141.82        174.50     198.73
Oxidation Catalyst    168.60      150.79         67.08      76.94
3-way Catalyst        132.70       93.37         23.93      23.07
Adaptive Learning     111.69      105.96         17.31      22.35

If we take some compounds listed as toxics under the Clean Air Act, then 
the 
beneficial effects of catalysts are obvious. Note that hexane and iso-
octane 
are the only alkanes listed as toxics, but benzene, toluene, ethyl 
benzene, 
o-xylene, m-xylene, and p-xylene are aromatics that are listed. The 
latter 
four are combined as C8 Aromatics below [43].
                        
Aromatics               FTP-weighted emission rates. (mg/mi)
                      Benzene          Toluene        C8 Aromatics
                    Gas   Reform     Gas   Reform     Gas   Reform
Noncatalyst       156.18  138.48   338.36  314.14   425.84  380.44
Oxidation Cat.     27.57   25.01    51.00   44.13    52.27   47.07
3-way Catalyst     19.39   15.69    36.62   26.14    42.38   29.03
Adaptive Learn.    19.77   20.39    29.98   29.67    35.01   32.40

Aldehydes               FTP-weighted emission rates. (mg/mi)
                    Formaldehyde      Acrolein        Acetaldehyde
                    Gas   Reform     Gas   Reform     Gas   Reform
Noncatalyst        73.25   85.24    11.62   13.20    19.74   21.72
Oxidation Cat.     28.50   35.83     3.74    3.75    11.15   11.76
3-way Catalyst      7.27    7.61     1.11    0.74     4.43    3.64
Adaptive Learn.     4.87    8.43     0.81    1.16     3.07    4.71

Others              1,3 Butadiene       MTBE
                    Gas   Reform     Gas   Reform
Noncatalyst         2.96    1.81    10.50  130.30  
Oxidation Cat.      0.02    0.33     2.43   11.83
3-way Catalyst      0.07    0.05     1.42    4.59
Adaptive Learn.     0.00    0.14     0.84    3.16

The author reports analytical problems with the 1,3 Butadiene, and only
Noncatalyst values are considered reliable.

Emission Standards

There are several bodies responsible for establishing standards, and 
they
promulgate test cycles, analysis procedures, and the % of new vehicles 
that 
must comply each year. The test cycles and procedures do change ( 
usually 
indicated by an anomalous increase in the numbers in the table ), and I 
have not listed the percentages of the vehicle fleet that are required 
to 
comply. This table is only intended to convey where we have been, and 
where 
we are going. It does not cover any regulation in detail - readers are 
advised to refer to the relevant regulations. Additional limits for 
other 
pollutants, such as formaldehyde and particulates, are omitted. The 1994 
tests signal the transition from 50,000 to 75,000 mile compliance 
testing, 
and I have not listed the subsequent 50,000 mile limits [60,61].
 
Year                    Federal                      California
                HCs    CO    NOx    Evap       HCs    CO    NOx    Evap
               g/mi   g/mi  g/mi   g/test     g/mi   g/mi  g/mi   g/test
Before regs   10.6   84.0   4.1    47        10.6   84.0   4.1    47
add crankcase +4.1                           +4.1 
1966                                          6.3   51.0   6.0
1968           6.3   51.0   6.0
1970           4.1   34.0                     4.1   34.0           6
1971           4.1   34.0                     4.1   34.0   4.0     6
1972           3.0   28.0                     2.9   34.0   3.0     2
1973           3.0   28.0   3.0               2.9   34.0   3.0     2
1974           3.0   28.0   3.0               2.9   34.0   2.0     2
1975           1.5   15.0   3.1     2         0.90   9.0   2.0     2
1977           1.5   15.0   2.0     2         0.41   9.0   1.5     2
1980           0.41   7.0   2.0     6         0.41   9.0   1.0     2
1981           0.41   3.4   1.0     2         0.39   7.0   0.7     2
1993           0.41   3.4   1.0     2         0.25   3.4   0.4     2
1994 50,000    0.26   3.4   0.3     ?   TLEV  0.13   3.4   0.4
1994 75,000    0.31   4.2   0.6     ?
1997                                    LEV   0.08   3.4   0.2
1997                                    ULEV  0.04   1.7   0.2
1998                                    ZEV   0.0    0.0   0.0   
2004           0.13   1.8   0.16    ?

It's also worth noting that exhaust catalysts also emit platinum, and 
the
soluble platinum salts are some of the most potent sensitizers known.
Early research [62] reported the presence of 10% water-soluble platinum 
in 
the emissions, however later work on monolithic catalysts has determined 
the
quantities of water soluble platinum emissions are negligible [63]. The 
particle size of the emissions has also been determined, and the 
emissions 
have been correlated with increasing vehicle speed. Increasing speed 
also 
increases the exhaust gas temperature and velocity, indicating the 
emissions 
are probably a consequence of physical attrition.

           Estimated Fuel                           Median Aerodynamic
Speed       Consumption         Emissions           Particle Diameter
km/h          l/100km            ng/m-3                    um
60              7                  3.3                     5.1           
100             8                 11.9                     4.2
140            10                 39.0                     5.6
US Cycle-75                        6.4                     8.5

Using the estimated fuel consumption, and about 10m3 of exhaust gas per 
litre of gasoline, the emissions are 2-40ng/km. These are 2-3 orders
of magnitude lower than earlier reported work on pelletised catalysts.
These emissions may be controlled directly in the future. They are 
currently 
indirectly controlled by the cost of platinum, and the new requirement 
for 
the catalyst to have an operational life of at least 100,000 miles.
                                                 
5.6  Why do exhaust catalysts influence fuel composition?

Modern adaptive learning engine management systems control the 
combustion
stoichiometry by monitoring various ambient and engine parameters, 
including
exhaust gas recirculation rates, the air flow sensor, and exhaust oxygen 
sensor outputs, This closed loop system using the oxygen sensor can 
compensate for changes in fuel content and air density. The oxygen 
sensor
is also known as the lambda sensor because the actual air/fuel mass 
ratio 
divided by the stoichiometric air/fuel mass ratio is known as lambda or 
the
air/fuel equivalence ratio. 

The preferred technique for describing mixture strength is the fuel-air 
equivalence ratio ( phi ), which is the actual fuel/air mass ratio 
divided 
by the stoichiometric fuel/air mass ratio, however most enthusiasts use 
air/fuel ratio and lambda. Lambda is the inverse of the fuel/air 
equivalence 
ratio. The oxygen sensor effectively measures lambda around the 
stoichiometric mixture point. Typical stoichiometric air/fuel ratios are 
[64]:- 
      6.4  methanol
      9.0  ethanol
     11.7  MTBE
     12.1  ETBE, TAME
     14.6  gasoline without oxygenates

The engine management system rapidly switches the stoichiometry between 
slightly rich and slightly lean, except under wide open throttle 
conditions 
- when the system runs open loop. The  response of the oxygen sensor to 
composition changes is about 3 ms, and closed loop switching is 
typically 
1-3 times a second, going between 50mV ( lambda = 1.05 (Lean)) to  900mV 
(lambda = 0.99 ( Rich)). The catalyst oxidises about 80% of the H2, CO, 
and HCs, and reduces the NOx [60]. 

Typical reactions that occur in a modern 3-way catalyst are:-
                2H2 + O2  ->  2H2O
                2CO + O2  ->  2CO2
    CxHy + (x + (y/4))O2  ->  xCO2 + (y/2)H2O
               2CO + 2NO  ->  N2 + 2CO2
   CxHy + 2(x + (y/4))NO  ->  (x + (y/4))N2 + (y/2)H2O + xCO2
               2H2 + 2NO  ->  N2 + 2H2O
                CO + H20  ->  CO2 + H2
             CxHy + xH2O  ->  xCO + (x + (y/2))H2          

The use of exhaust catalysts have resulted in reaction pathways that can 
accidentally be responsible for increased pollution. An example is the 
CARB-mandated reduction of fuel sulfur. A change from 450ppm to 50ppm, 
which 
will reduce HC & CO emissions by 20%, may increase formaldehyde by 45% 
[24]. 

The requirement that the exhaust catalysts must now endure for 10 years 
or 
100,000 miles will also encourage automakers to push for lower levels of 
known catalyst "poisons" such as sulfur and phosphorus in both the 
gasoline 
and lubricant. Modern catalysts are unable to reduce the relatively high 
levels of NOx that are produced during lean operation down to approved 
levels, thus preventing the application of lean-burn engine technology. 
Recently Mazda has announced they have developed a "lean burn" catalyst, 
which may enable automakers to move the fuel combustion towards the lean 
side, and different gasoline properties may be required to optimise the
combustion and reduce pollution [65]. Mazda claim that fuel efficiency 
is 
improved by 5-8% while meeting all emission regulations, and some 
Japanese
manufacturers have evaluated lean-burn catalysts in limited numbers of 
1995 
production models. 

Catalysts also inhibit the selection of gasoline octane-improving and 
cleanliness additives ( such as MMT and phosphorus-containing additives 
) 
that may result in refractory compounds known to physically coat the 
catalyst, reducing available catalyst and thus increasing pollution. 

5.7  Why are "cold start" emissions so important?

The catalyst requires heat to reach the temperature ( >300-350C ) where 
it 
functions most efficiently, and the delay until it reaches operating 
temperature can produce more hydrocarbons than would be produced during 
the remainder of many typical urban short trips. It has been estimated 
that
70-80% of the non-methane HCs that escape conversion by the catalysts 
are emitted during the first two minutes after a cold start. As exhaust 
emissions have been reduced, the significance of the evaporative 
emissions 
increases. Several engineering techniques are being developed, including 
the 
Ford Exhaust Gas Igniter ( uses a flame to heat the catalyst - lots of 
potential problems ), zeolite hydrocarbon traps, and relocation of the
catalyst closer to the engine [60]. 

Reduced gasoline volatility and composition changes, along with 
cleanliness 
additives and engine management systems, can help minimise cold start 
emissions, but currently the most effective technique appears to be 
rapid, 
deliberate heating of the catalyst, and the new generation of low 
thermal 
inertia  "fast light-up" catalysts reduce the problem, but further 
research 
is necessary [60,66].

As the evaporative emissions are also starting to be reduced, the 
emphasis
has shifted to the refuelling emissions. These will be mainly controlled
on the vehicle, and larger canisters may be used to trap the vapours 
emitted
during refuelling. 

5.8  When will the emissions be "clean enough"?

The California ZEV regulations effectively preclude IC vehicles, because
they stipulate zero emissions. However, the concept of regulatory 
forcing
of alternative vehicle propulsion technology may have to be modified to
include hybrid or fuel-cell vehicles, as the major failing of EVs 
remains
the lack of a cheap, light, safe, and  easily-rechargeable electrical 

_
                                                             

storage device [67,68]. There are several major projects intending to 
further reduce emissions from automobiles, mainly focusing on vehicle 
mass 
and engine fuel efficiency, but gasoline specifications and alternative 
fuels are also being investigated. It may be that changes to IC engines 
and 
gasolines will enable the IC engine to continue well into the 21st 
century 
as the prime motive force for personal transportation [61,69]. There 
have 
also been calls to use market forces to reduce pollution from 
automobiles 
[70], however most such suggestions ( increased gasoline taxes, 
congestion 
tolls, and emission-based registration fees ) are currently considered 
politically unacceptable. The issue of how to target the specific "gross 
polluters" is being considered, and is described in Section 5.14.

5.9  Why are only some gasoline compounds restricted?

The less volatile hydrocarbons in gasoline are not released in 
significant 
quantities during normal use, and the more volatile alkanes are 
considerably
less toxic than many other chemicals encountered daily. The newer 
gasoline 
additives also have potentially undesirable properties before they are 
even
combusted. Most hydrocarbons are very insoluble in water, with the lower
aromatics being the most soluble, however the addition of oxygen to 
hydrocarbons significantly increases the mutual solubility with water.

                      Compound in Water            Water in Compound       
                      % mass/mass @  C             % mass/mass @  C
normal decane            0.0000052  25               0.0072      25
iso-octane               0.00024    25               0.0055      20
normal hexane            0.00125    25               0.0111      20
cyclohexane              0.0055     25               0.010       20
1-hexene                 0.00697    25               0.0477      30
toluene                  0.0515     25               0.0334      25
benzene                  0.1791     25               0.0635      25

methanol                complete    25              complete     25
ethanol                 complete    25              complete     25 
MTBE                     4.8        20               1.4         20
TAME                      -                          0.6         20
          
The concentrations and ratios of benzene, toluene, ethyl benzene, and 
xylenes 
( BTEX ) in water are often used to monitor groundwater contamination 
from
gasoline storage tanks or pipelines. The oxygenates and other new 
additives 
may increase the extent of water and soil pollution by acting as co-
solvents 
for HCs. 

Various government bodies ( EPA, OSHA, NIOSH ) are charged with ensuring
people are not exposed to unacceptable chemical hazards, and maintain
ongoing research into the toxicity of liquid gasoline contact, water and 
soil
pollution, evaporative emissions, and tailpipe emissions [71]. As 
toxicity 
is found, the quantities in gasoline of the specific chemical ( benzene 
), 
or family of chemicals ( alkyl leads, aromatics, olefins ) are 
regulated.

The recent dramatic changes caused by the need to reduce alkyl leads,
halogens, olefins, and aromatics has resulted in whole new families of 
compounds ( ethers, alcohols ) being introduced into fuels without prior 
detailed toxicity studies being completed. If adverse results appear, 
these 
compounds are also likely to be regulated to protect people and the 
environment. 

Also, as the chemistry of emissions is unravelled, the chemical 
precursors
to toxic tailpipe emissions ( such as higher aromatics that produce 
benzene  
emissions ) are also controlled, even if they are not themselves toxic.

5.10 What does "renewable" fuel/oxygenate mean?

The general definition of "renewable" is that the carbon originates from 
recent biomass, and thus does not contribute to the increased CO2 
emissions. 
A truly "long-term" view could claim that fossil fuels are "renewable" 
on a
100 million year timescale :-). There was a major battle between the 
ethanol/ETBE lobby ( agricultural, corn growing ), and the methanol/MTBE 
lobby ( oil company, petrochemical ) over an EPA mandate demanding that 
a
specific percentage of the oxygenates in gasoline are produced from 
"renewable" sources [72]. On 28 April 1995 a Federal appeals court 
permanently voided the EPA ruling requiring "renewable" oxygenates, thus
fossil-fuel derived oxygenates such as MTBE are acceptable oxygenates 
[73]. 

Unfortunately, "renewable" ethanol is not cost competitive when crude 
oil 
is $18/bbl, so a federal subsidy ( $0.54/US Gallon ) and additional 
state 
subsidies ( 11 states - from $0.08(Michigan) to $0.66(Tenn.)/US Gal.) 
are 
provided. Ethanol, and ETBE derived from ethanol, are still likely to be 
used in states where subsidies make them competitive with other 
oxygenates. 

5.11 Will oxygenated gasoline damage my vehicle?

The following comments assume that your vehicle was designed to operate 
on 
unleaded, if not, then damage like valve seat recession may also occur. 
Damage should not occur if the gasoline is correctly formulated, and you 
select the appropriate octane, but oxygenated gasoline will hurt your 
pocket.
In the first year of mandated oxygenates, it appears some refiners did 
not 
carefully formulate their oxygenated gasoline, and driveability and 
emissions 
problems occurred. Most reputable brands are now carefully formulated. 
Some older activated carbon canisters may not function efficiently with
oxygenated gasolines, but this is a function of the type of carbon used.
How your vehicle responds to oxygenated gasoline depends on the engine 
management system and state of tune. A modern system will automatically 
compensate for all of the currently-permitted oxygenate levels, thus 
your
fuel consumption will increase. Older, poorly-maintained, engines may 
require a tune up to maintain acceptable driveability.

Be prepared to try several different brands of oxygenated or 
reformulated 
gasolines to identify the most suitable brand for your vehicle, and be 
prepared to change again with the seasons. This is because the refiners 
can 
choose the oxygenate they use to meet the regulations, and may choose to 
set 
some fuel properties, such as volatility, differently to their 
competitors. 

Most stories of corrosion etc, are derived from anhydrous methanol 
corrosion 
of light metals (aluminum, magnesium), however the addition of either 
0.5% 
water to pure methanol, or corrosion inhibitors to methanol/gasoline 
blends 
will prevent this. If you observe corrosion, talk to your gasoline 
supplier.  
Oxygenated fuels may either swell or shrink some elastomers on older 
cars, 
depending on the aromatic and olefin content of the fuels. Cars later 
than 
1990 should not experience compatibility problems, and cars later than 
1994 
should not experience driveability problems, but they will experience 
increased fuel consumption, depending on the state of tune and engine 
management system.  
          
5.12 What does "reactivity" of emissions mean?

The traditional method of exhaust regulations was to specify the actual 
HC, 
CO, NOx, and particulate contents. With the introduction of oxygenates 
and 
reformulated gasolines, the volatile organic carbon (VOC) species in the 
exhaust also changed. The "reactivity" refers to the ozone-forming 
potential 
of the VOC emissions when they react with NOx, and is being introduced 
as a 
regulatory means of ensuring that automobile emissions do actually 
reduce 
smog formation. The ozone-forming potential of chemicals is defined as 
the 
number of molecules of ozone formed per VOC carbon atom, and this is 
called 
the Incremental Reactivity. Typical values ( big is bad :-) ) are [58]: 

Maximum Incremental Reactivities as mg Ozone / mg VOC 

                  carbon monoxide           0.054
alkanes           methane                   0.0148
                  ethane                    0.25
                  propane                   0.48
                  n-butane                  1.02
olefins           ethylene                  7.29
                  propylene                 9.40
                  1,3 butadiene            10.89
aromatics         benzene                   0.42
                  toluene                   2.73
                  meta-xylene               8.15      
                  1,3,5-trimethyl benzene  10.12
oxygenates        methanol                  0.56
                  ethanol                   1.34
                  MTBE                      0.62
                  ETBE                      1.98

5.13 What are "carbonyl" compounds?

Carbonyls are produced in large amounts under lean operating conditions,
especially when oxygenated fuels are used. Most carbonyls are toxic, and 
the 
carboxylic acids can corrode metals. The emission of carbonyls can be 
controlled by combustion stoichiometry and exhaust catalysts, refer to
section 5.5 for typical reductions for aldehydes.  
Typical carbonyls are:-
* aldehydes ( containing -CHO ),
  - formaldehyde (HCHO) - which is formed in large amounts during lean 
                          combustion of methanol [74].
  - acetaldehyde (CH2CHO) - which is formed during ethanol combustion. 
  - acrolein (CH2=CHCHO) - a very potent irritant and toxin.
* ketones ( containing C=0 ),
  - acetone (CH3COCH3)
* carboxylic acids ( containing -COOH ),
  - formic acid (HCOOH) - formed during lean methanol combustion. 
  - acetic acid (CH3COOH). 

5.14 What are "gross polluters"? 

It has always been known that the EPA emissions tests do not reflect 
real 
world conditions. There have been several attempts to identify vehicles 
on 
the road that do not comply with emissions standards. Recent remote 
sensing 
surveys have demonstrated that the highest 10% of CO emitters produce 
over 
50% of the pollution, and the same ratio applies for the HC emitters 
- which may not be the same vehicles [75-86]. 20% of the CO emitters are 
responsible for 80% of the CO emissions, consequently modifying gasoline 
composition is only one aspect of pollution reduction. The new additives 
can 
help maintain engine condition, but they can not compensate for out-of-
tune,
worn, or tampered-with engines.

The most famous of these remote sensing systems is the FEAT ( Fuel 
Efficiency 
Automobile Test ) team from the University of Denver [78]. This team is 
probably the world leader in remote sensing of auto emissions to 
identify 
grossly polluting vehicles. The system measures CO/CO2 ratio, and the 
HC/CO2 ratio in the exhaust of vehicles passing through an infra-red 
light 
beam crossing the road 25cm above the surface. The system also includes 
a 
video system that records the licence plate, date, time, calculated 
exhaust 
CO, CO2, and HC. The system is effective for traffic lanes up to 18 
metres
wide, however rain, snow, and water spray can cause scattering of the 
beam.
Reference signals monitor such effects and, if possible, compensate. The
system has been comprehensively validated, including using vehicles with 
on-board emissions monitoring instruments.

They can monitor up to 1000 vehicles an hour and, as an example,they 
were 
invited to Provo, Utah to monitor vehicles, and gross polluters would be 
offered free repairs [84]. They monitored over 10,000 vehicles and 
mailed 
114 letters to owners of vehicles newer than 1965 that had demonstrated 
high 
CO levels. They received 52 responses and repairs started in Dec. 1991, 
and 
continued to Mar 1992. They offered to purchase two vehicles at blue 
book 
price.  They were declined, and so attempted to modify those vehicles, 
even
though their condition did not justify the expense. 
  
 The entire monitored fleet at Provo (Utah) during Winter 1991/1992 
 Model year               Grams CO/gallon            Number of
                    (Median value) (mean value)      Vehicles
   92                    40             80              247
   91                    55                            1222
   90                    75                            1467
   89                    80                            1512
   88                    85                            1651
   87                    90                            1439
   86                   100            300             1563
   85                   120                            1575
   84                   125                            1206
   83                   145                             719
   82                   170                             639
   81                   230                             612
   80                   220            500              551
   79                   350                             667
   78                   420                             584
   77                   430                             430
   76                   770                             317
   75                   760            950              163
   Pre 75               920           1060              878

As observed elsewhere, over half the CO was emitted by about 10% of the 
vehicles. If the 47 worst polluting vehicles were removed, that achieves 
more than removing the 2,500 lowest emitting vehicles from the total 
tested 
fleet.

Surveys of vehicle populations have demonstrated that emissions systems 
had 
been tampered with on over 40% of the gross polluters, and an additional 
20% 
had defective emission control equipment [85]. No matter what changes 
are 
made to gasoline, if owners "tune" their engines for power, then the 
majority
of such "tuned" vehicle will become gross polluters. Professional 
repairs to 
gross polluters usually improves fuel consumption, resulting in a low 
cost to
owners ( $32/pa/Ton CO year ). The removal of CO in the Provo example 
above 
was costed at $200/Ton CO, compared to Inspection and Maintenance 
programs 
($780/Ton CO ), and oxygenates ( $1034-$1264/Ton CO in Colorado 1991-2 
), and
UNOCALs vehicle scrapping programme ( $1025/Ton of all pollutants ).

Thus, identifying and repairing or removing gross polluters can be far 
more 
cost-effective than playing around with reformulated gasolines and 
oxygenates. A recent study has confirmed that gross polluters are not 
always
older vehicles, and that vehicles have been scrapped that passed the 
1993 new
vehicle emission standards [86]. The study also confirmed that if 
estimated
costs and benefits of various emission reduction strategies were applied 
to
the tested fleet, the identification and repair techniques are the most 
cost-effective means of reducing HC and CO. It should be noted that some 
strategies ( such as the use of oxygenates to replace aromatics and 
alkyl 
lead compounds ) have other environmental benefits. 

Action                      Vehicles      Estimated        % reduction 
                            Affected        Cost            billion $
                           (millions)    (billion $)        HC    CO
Reformulated Fuels            20            1.5            11     7.3
Scrap pre-1980 vehicles        3.2          2.2            15    19
Scrap pre-1988 vehicles       14.6         17               2.6   3.9
Repair worst 20% of vehicles   4            0.88           57     69
Repair worst 40% of vehicles   8            1.76           39     47

------------------------------



                                                                              

waikato!comp.vuw.ac.nz!zephyr.grace.cri.nz!usenet



Archive-name: autos/gasoline-faq/part3


6.1  Who invented Octane Ratings?

Since 1912 the spark ignition internal combustion engine's compression 
ratio 
had been constrained by the unwanted "knock" that could rapidly destroy 
engines. "Knocking" is a very good description of the sound heard from 
an 
engine using fuel of too low octane. The engineers had blamed the 
"knock" 
on the battery ignition system that was added to cars along with the 
electric self-starter. The engine developers knew that they could 
improve 
power and efficiency if knock could be overcome. 

Kettering assigned Thomas Midgley, Jr. to the task of finding the exact 
cause of knock [17]. They used a Dobbie-McInnes manograph to demonstrate 
that the knock did not arise from preignition, as was commonly supposed, 
but
arose from a violent pressure rise _after_ ignition. The manograph was 
not
suitable for further research, so Midgley and Boyd developed a high-
speed 
camera to see what was happening. They also developed a "bouncing pin" 
indicator that measured the amount of knock [8]. Ricardo had developed 
an
alternative concept of HUCF ( Highest Useful Compression Ratio ) using a 
variable-compression engine. His numbers were not absolute, as there 
were 
many variables, such as ignition timing, cleanliness, spark plug 
position, 
engine temperature. etc.
   
In 1926 Graham Edgar suggested using two hydrocarbons that could be 
produced 
in sufficient purity and quantity [10]. These were "normal heptane", 
that 
was already obtainable in sufficient purity from the distillation of 
Jeffrey 
pine oil, and " an octane, named 2,4,4-trimethyl pentane " that he first 
synthesized. Today we call it " iso-octane " or 2,2,4-trimethyl pentane. 
The 
octane had a high anti-knock value, and he suggested using the ratio of 
the 
two as a reference fuel number. He demonstrated that all the 
commercially- 
available gasolines could be bracketed between 60:40 and 40:60 parts by 
volume heptane:iso-octane.

The reason for using normal heptane and iso-octane was because they both 
have similar volatility properties, specifically boiling point, thus the 
varying ratios 0:100 to 100:0 should not exhibit large differences in 
volatility that could affect the rating test.
                                                           Heat of
               Melting Point  Boiling Point  Density    Vaporisation
                     C              C          g/ml         MJ/kg
normal heptane    -90.7           98.4       0.684          0.365 @ 25C
iso octane       -107.45          99.3       0.6919         0.308 @ 25C

Having decided on standard reference fuels, a whole range of engines and
test conditions appeared, but today the most common are the Research 
Octane
Number ( RON ), and the Motor Octane Number ( MON ).

6.2  Why do we need Octane Ratings?

To obtain the maximum energy from the gasoline, the compressed fuel/air 
mixture inside the combustion chamber needs to burn evenly, propagating 
out 
from the spark plug until all the fuel is consumed. This would deliver 
an 
optimum power stroke. In real life, a series of pre-flame reactions will 
occur in the unburnt "end gases" in the combustion chamber before the 
flame 
front arrives. If these reactions form molecules or species that can 
autoignite before the flame front arrives, knock will occur [14,15].
 
Simply put, the octane rating of the fuel reflects the ability of the 
unburnt end gases to resist spontaneous autoignition under the engine 
test
conditions used. If autoignition occurs, it results in an extremely 
rapid 
pressure rise, as both the desired spark-initiated flame front, and the 
undesired autoignited end gas flames are expanding. The combined 
pressure 
peak arrives slightly ahead of the normal operating pressure peak, 
leading 
to a loss of power and eventual overheating. The end gas pressure waves 
are 
superimposed on the main pressure wave, leading to a sawtooth pattern of 
pressure oscillations that create the "knocking" sound.

The combination of intense pressure waves and overheating can induce 
piston 
failure in a few minutes. Knock and preignition are both favoured by 
high 
temperatures, so one may lead to the other. Under high-speed conditions 
knock can lead to preignition, which then accelerates engine destruction 
[20].

6.3  What fuel property does the Octane Rating measure?

The fuel property the octane ratings measure is the ability of the 
unburnt
end gases to spontaneously ignite under the specified test conditions.
Within the chemical structure of the fuel is the ability to withstand  
pre-flame conditions without decomposing into species that will 
autoignite 
before the flame-front arrives. Different reaction mechanisms, occurring 
at
various stages of the pre-flame compression stroke, are responsible for 
the 
undesirable, easily-autoignitable, end gases.

During the oxidation of a hydrocarbon fuel, the hydrogen atoms are 
removed 
one at a time from the molecule by reactions with small radical species
(such as OH and HO2), and O and H atoms. The strength of carbon-hydrogen
bonds depends on what the carbon is connected to. Straight chain HCs 
such as
normal heptane have secondary C-H bonds that are significantly weaker 
than
the primary C-H bonds present in branched chain HCs like iso-octane 
[14,15].


The octane rating of hydrocarbons is determined by the structure of the 
molecule, with long, straight hydrocarbon chains producing large amounts 
of 
easily-autoignitable pre-flame decomposition species, while branched and 
aromatic hydrocarbons are more resistant. This also explains why the 
octane
ratings of paraffins consistently decrease with carbon number. In real 
life, 
the unburnt "end gases" ahead of the flame front encounter temperatures 
up 
to about 700C due to piston motion and radiant and conductive heating, 
and 
commence a series of pre-flame reactions. These reactions occur at 
different 
thermal stages, with the initial stage ( below 400C ) commencing with 
the 
addition of molecular oxygen to alkyl radicals, followed by the internal 
transfer of hydrogen atoms within the new radical to form an 
unsaturated, 
oxygen-containing species. These new species are susceptible to chain 
branching involving the HO2 radical during the intermediate temperature 
stage (400-600C), mainly through the production of OH radicals. Above 
600C, 
the most important reaction that produces chain branching is the 
reaction of 
one hydrogen atom radical with molecular oxygen to form O and OH 
radicals.

The addition of additives such as alkyl lead and oxygenates can 
significantly affect the pre-flame reaction pathways. Anti-knock 
additives 
work by interfering at different points in the pre-flame reactions, with
the oxygenates retarding undesirable low temperature reactions, and the
alkyl lead compounds react in the intermediate temperature region to 
deactivate the major undesirable chain branching sequence [14,15]. 

The antiknock ability is related to the "autoignition temperature" of 
the 
hydrocarbons. Antiknock ability is _not_ substantially related to:-
1. The energy content of fuel, this should be obvious, as oxygenates 
have 
   lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be
   evident from the similarities of the two reference hydrocarbons. 
   Although flame speed does play a minor part, there are many other 
factors 
   that are far more important. ( such as compression ratio, 
stoichiometry,
   combustion chamber shape, chemical structure of the fuel, presence of 
   antiknock additives, number and position of spark plugs, turbulence 
etc.)
   Flame speed does not correlate with octane.

6.4  Why are two ratings used to obtain the pump rating?

The correct name for the (RON+MON)/2 formula is the "antiknock index",
and it remains the most important quality criteria for motorists [31].

The initial octane method developed in the 1920s was the Motor Octane 
method 
and, over several decades, a large number of octane test methods 
appeared. 
These were variations to either the engine design, or the specified 
operating 
conditions [87]. During the 1950-1960s attempts were made to 
internationally 
standardise and reduce the number of Octane Rating test procedures.

During the late 1930s - mid 1960s, the Research method became the 
important 
rating because it more closely represented the octane requirements of 
the 
motorist using the fuels/vehicles/roads then available. In the late 
1960s 
German automakers discovered their engines were destroying themselves on 
long Autobahn runs, even though the Research Octane was within 
specification. 
They discovered that either the MON or the Sensitivity ( the numerical 
difference between the RON and MON numbers ) also had to be specified. 
Today 
it is accepted that no one octane rating covers all use. In fact, during 
1994, there have been increasing concerns in Europe about the high 
Sensitivity of some commercially-available unleaded fuels.

The design of the engine and car significantly affect the fuel octane 
requirement for both RON and MON. In the 1930s, most vehicles would run 
on 
the specified Research Octane fuel, almost regardless of the Motor 
Octane, 
whereas most 1990s engines have a 'severity" of one, which means the 
engine
is unlikely to knock if a changes of one RON is matched by an equal and 
opposite change of MON [24].

6.5  What does the Motor Octane rating measure?

The conditions of the Motor method represent severe, sustained high 
speed, 
high load driving. For most hydrocarbon fuels, including those with 
either 
lead or oxygenates, the motor octane number (MON) will be lower than the 
research octane number (RON).

Test Engine conditions                Motor Octane 
Test Method                         ASTM D2700-92 [88]
Engine                       Cooperative Fuels Research ( CFR )
Engine RPM                               900 RPM
Intake air temperature                    38 C
Intake air humidity           3.56 - 7.12 g H2O / kg dry air        
Intake mixture temperature               149 C 
Coolant temperature                      100 C
Oil Temperature                           57 C
Ignition Advance - variable     Varies with compression ratio
                                 ( eg 14 - 26 degrees BTDC ) 
Carburettor Venturi                       14.3 mm

6.6  What does the Research Octane rating measure?

The Research method settings represent typical mild driving, without
consistent heavy loads on the engine.

Test Engine conditions               Research Octane
Test Method                         ASTM D2699-92 [89]
Engine                       Cooperative Fuels Research ( CFR )       
Engine RPM                               600 RPM
Intake air temperature       Varies with barometric pressure 
                           ( eg 88kPa = 19.4C, 101.6kPa = 52.2C )

Intake air humidity           3.56 - 7.12 g H2O / kg dry air
Intake mixture temperature            Not specified 
Coolant temperature                      100 C
Oil Temperature                           57 C
Ignition Advance - fixed            13 degrees BTDC 
Carburettor Venturi           Set according to engine altitude          
                           ( eg 0-500m=14.3mm, 500-1000m=15.1mm ) 

6.7  Why is the difference called "sensitivity"?

RON - MON = Sensitivity. Because the two test methods use different test 
conditions, especially the intake mixture temperatures and engine 
speeds, 
then a fuel that is sensitive to changes in operating conditions will 
have 
a larger difference between the two rating methods. Modern fuels 
typically 
have sensitivities around 10. The US 87 (RON+MON/2) unleaded gasoline is 
required to have a 82+ MON, thus preventing very high sensitivity fuels 
[31].

Recent changes in Europeon gasolines has caused concern, as high 
sensitivity
unleaded fuels have been found that fail to meet the 85 MON requirement 
of 
the EN228 European gasoline specification [90]. 

6.8  What sort of engine is used to rate fuels?

Automotive octane ratings are determined in a special single-cylinder 
engine 
with a variable compression ratio ( CR 4:1 to 18:1 ) known as a 
Cooperative 
Fuels Research ( CFR ) engine. The cylinder bore is 82.5mm, the stroke 
is 
114.3mm, giving a displacement of 612 cm3. The piston has four 
compression 
rings, and one oil control ring. The intake valve is shrouded. The head 
and 
cylinder are one piece, and can be moved up and down to obtain the 
desired 
compression ratio.  The engines have a special four-bowl carburettor 
that 
can adjust individual bowl air/fuel ratios. This facilitates rapid 
switching 
between reference fuels and samples. A magnetorestrictive detonation 
sensor 
in the combustion chamber measures the rapid changes in combustion 
chamber 
pressure caused by knock, and the amplified signal is measured on a 
"knockmeter" with a 0-100 scale [88,89]. A complete Octane Rating engine 
system costs about $200,000 with all the services installed. Only one 
company manufactures these engines, the Waukesha Engine Division of 
Dresser 
Industries, Waukesha. WI 53186.
          
6.9  How is the Octane rating determined?

To rate a fuel, the engine is set to an appropriate compression ratio 
that 
will produce a knock of about 50 on the knockmeter for the sample when 
the 
air/fuel ratio is adjusted on the carburettor bowl to obtain maximum 
knock. 
Normal heptane and iso-octane are known as primary reference fuels. Two 
blends of these are made, one that is one octane number above the 
expected 
rating, and another that is one octane number below the expected rating. 
These are placed in different bowls, and are also rated with each 
air/fuel
ratio being adjusted for maximum knock. The higher octane reference fuel 
should produce a reading around 30-40, and the lower reference fuel 
should
produce a reading of 60-70. The sample is again tested, and if it does 
not 
fit between the reference fuels, further reference fuels are prepared, 
and 
the engine readjusted to obtain the required knock. The actual fuel 
rating 
is interpolated from the knockmeter readings [88,89].  

6.10 What is the Octane Distribution of the fuel?

The combination of vehicle and engine can result in specific 
requirements
for octane that depend on the fuel. If the octane is distributed 
differently 
throughout the boiling range of a fuel, then engines can knock on one 
brand 
of 87 (RON+MON/2), but not on another brand. This "octane distribution" 
is 
especially important when sudden changes in load occur, such as high 
load,
full throttle, acceleration. The fuel can segregate in the manifold, 
with 
the very volatile fraction reaching the combustion chamber first and, if 
that fraction is deficient in octane, then knock will occur until the 
less 
volatile, higher octane fractions arrive [20]. 

Some fuel specifications include delta RONs, to ensure octane 
distribution 
throughout the fuel boiling range was consistent. Octane distribution 
was 
seldom a problem with the alkyl lead compounds, as the tetra methyl lead
and tetra ethyl lead octane volatility profiles were well characterised, 
but 
it can be a major problem for the new, reformulated, low aromatic 
gasolines, 
as MTBE boils at 55C, whereas ethanol boils at 78C. Drivers have 
discovered
that an 87 (RON+MON/2) from one brand has to be substituted with an 89
(RON+MON/2) of another, and that is because of the combination of their 
driving style, engine design, vehicle mass, fuel octane distribution, 
fuel 
volatility, and the octane-enhancers used.
          
6.11 What is a "delta Research Octane number"?

To obtain an indication of behaviour of a gasoline during any manifold 
segregation, an octane rating procedure called the Distribution Octane 
Number was used. The rating engine had a special manifold that allowed 
the heavier fractions to be separated before they reached the combustion 
chamber [20]. That method has been replaced by the "delta" RON 
procedure. 

The fuel is carefully distilled to obtain a distillate fraction that 
boils 
to the specified temperature, which is usually 100C. Both the parent 
fuel 
and the distillate fraction are rated on the  octane engine using the 
Research Octane method [91]. The difference between these is the delta 
RON(100C), usually just called the delta RON.

6.12 How do other fuel properties affect octane?

Several other properties affect knock. The most significant determinant 
of 
octane is the chemical structure of the hydrocarbons and their response 
to 
the addition of octane enhancing additives. Other factors include:-
Front End Volatility - Paraffins are the major component in gasoline, 
and 
  the octane number decreases with increasing chain length or ring size, 
but 
  increases with chain branching. Overall, the effect is a significant 
  reduction in octane if front end volatility is lost, as can happen 
with 
  improper or long term storage. Fuel economy on short trips can be 
improved 
  by using a more volatile fuel, at the risk of carburettor icing and 
  increased evaporative emissions. 
Final Boiling Point.- Decreases in the final boiling point increase fuel 
  octane. Aviation gasolines have much lower final boiling points than 
  automotive gasolines. Note that final boiling points are being reduced
  because the higher boiling fractions are responsible for 
disproportionate
  quantities of pollutants and toxins. 
Preignition tendency - both knock and preignition can induce each other.

6.13 Can higher octane fuels give me more power?

On modern engines with sophisticated engine management systems, the 
engine
can operate efficiently on fuels of a wider range of octane rating, but 
there 
remains an optimum octane for the engine under specific driving 
conditions. 
Older cars without such systems are more restricted in their choice of 
fuel, 
as the engine can not automatically adjust to accommodate lower octane 
fuel.
Because knock is so destructive, owners of older cars must use fuel that 
will 
not knock under the most demanding conditions they encounter, and must 
continue to use that fuel, even if they only occasionally require the 
octane. 


If you are already using the proper octane fuel, you will not obtain 
more
power from higher octane fuels. The engine will be already operating at 
optimum settings, and a higher octane should have no effect on the 
management
system. Your driveability and fuel economy will remain the same. The 
higher 
octane fuel costs more, so you are just throwing money away. If you are 
already using a fuel with an octane rating slightly below the optimum, 
then 
using a higher octane fuel will cause the engine management system to 
move to
the optimum settings, possibly resulting in both increased power and 
improved
fuel economy. You may be able to change octanes between seasons ( reduce 
octane in winter ) to obtain the most cost-effective fuel without loss 
of 
driveability. 

Once you have identified the fuel that keeps the engine at optimum 
settings, 
there is no advantage in moving to an even higher octane fuel. The 

_
     

manufacturer's recommendation is conservative, so you may be able to 
carefully reduce the fuel octane. The penalty for getting it badly 
wrong, 
and not realising that you have, could be expensive engine damage. 

6.14 Does low octane fuel increase engine wear?

Not if you are meeting the octane requirement of the engine. If you are 
not
meeting the octane requirement, the engine will rapidly suffer major 
damage 
due to knock. You must not use fuels that produce sustained audible 
knock,
engine damage will occur. If the octane is just sufficient, the engine 
management system will move settings to a less optimal position, and the 
only major penalty will be increased costs due to poor fuel economy. 
Whenever possible, engines should be operated at the optimum position 
for 
long-term reliability. Engine wear is mainly related to design, 
manufacturing, maintenance and lubrication factors. Once the octane and 
run-on requirements of the engine are satisfied, increased octane will 
have 
no beneficial effect on the engine. The quality of gasoline, and the 
additive package used, would be more likely to affect the rate of engine 
wear, rather than the octane rating. 

6.15 Can I mix different octane fuel grades?

Yes, however attempts to blend in your fuel tank should be carefully
planned. You should not allow the tank to become empty, and then add 50% 
of 
lower octane, followed by 50% of higher octane. The fuels may not 
completely 
mix immediately, especially if there is a density difference. You may 
get a 
slug of low octane that causes severe knock. You should refill when your 
tank is half full. In general the octane response will be linear for 
most 
hydrocarbon and oxygenated fuels eg 50:50 of 87 and 91 will give 89. 

Attempts to mix leaded high octane to unleaded high octane to obtain 
higher 
octane are useless. The lead response of the unleaded fuel does not 
overcome 
the dilution effect, thus 50:50 of 96 leaded and 91 unleaded will give 
94.
Some blends of oxygenated fuels with ordinary gasoline can result in
undesirable increases in volatility due to volatile azeotropes, and that 
some oxygenates can have negative lead responses. Also note that the 
octane 
requirement of some engines is determined by the need to avoid run-on, 
not 
to avoid knock.

6.16 What happens if I use the wrong octane fuel?
          
If you use a fuel with an octane rating below the requirement of the 
engine, 
the management system may move the engine settings into an area of less 
efficient combustion, resulting in reduced power and reduced fuel 
economy.
You will be losing both money and driveability. If you use a fuel with 
an 
octane rating higher than what the engine can use, you are just wasting 
money by paying for octane that you can not utilise. Forget the stories 
about higher octanes having superior additive packages - they do not. If 
your vehicle does not have a knock sensor, then using an octane 
significantly 
below the requirement means that the little men with hammers will 
gleefully 
pummel your engine to pieces. 

You should initially be guided by the vehicle manufacturer's 
recommendations, 
however you can experiment, as the variations in vehicle tolerances can 
mean that Octane Number Requirement for a given vehicle model can range 
over 6 Octane Numbers. Caution should be used, and remember to 
compensate 
if the conditions change, such as carrying more people or driving in 
different ambient conditions. You can often reduce the octane of the 
fuel 
you use in winter because the temperature decrease and possible humidity 
changes may significantly reduce the octane requirement of the engine.

Use the octane that provides cost-effective driveability and 
performance, 
using anything more is waste of money, and anything less could result in
an unscheduled, expensive visit to your mechanic.

6.17 Can I tune the engine to use another octane fuel?

In general, modern engine management systems will compensate for fuel 
octane, 
and once you have satisfied the optimum octane requirement, you are at 
the
optimum overall performance area of the engine map. Tuning changes to 
obtain 
more power will probably adversely affect both fuel economy and 
emissions. 
Unless you have access to good diagnostic equipment that can ensure 
regulatory limits are complied with, it is likely that adjustments may 
be 
regarded as illegal tampering by your local regulation enforcers. If you 
are 
skilled, you will be able to legally wring slightly more performance 
from 
your engine by using a dynamometer in conjunction with engine and 
exhaust gas
analyzers and a well-designed, retrofitted, performance engine 
management 
chip.

6.18 How can I increase the fuel octane?

Not simply, you can purchase additives, however these are not cost-
effective
and a survey in 1989 showed the cost of increasing the octane rating of 
one
US gallon by one unit ranged from 10 cents ( methanol ), 50 cents (MMT), 
$1.00 ( TEL ), to $3.25 ( xylenes ) [92]. Refer to section 6.20 for a 
discussion on naphthalene ( mothballs ). It is preferable to purchase a 
higher octane fuel such as racing fuel, aviation gasolines, or methanol. 
Sadly, the price of chemical grade methanol has almost doubled during 
1994. 
If you plan to use alcohol blends, ensure your fuel handling system is 
compatible, and that you only use dry gasoline by filling up early in 
the 
morning when the storage tanks are cool. Also ensure that the service 
station
storage tank has not been refilled recently. Retailers are supposed to 
wait 
several hours before bringing a refilled tank online, to allow suspended 
undissolved water to settle out, but they do not always wait the full 
period. 

6.19 Are aviation gasoline octane numbers comparable?

Aviation gasolines were all highly leaded and graded using two numbers, 
with 
common grades being 80/87, 100/130, and 115/145 [93,94]. The first 
number is 
the Aviation rating ( aka Lean Mixture rating ), and the second number 
is the 
Supercharge rating ( aka Rich Mixture rating ). In the 1970s a new 
grade,
100LL ( low lead = 0.53mlTEL/L instead of 1.06mlTEL/L) was introduced to 
replace the 80/87 and 100/130. Soon after the introduction, there was a 
spate of plug fouling, and high cylinder head temperatures resulting in 
cracked cylinder heads [94]. The old 80/87 grade was reintroduced on a 
limited scale.  The Aviation rating is determined using the automotive 
Motor 
Octane test procedure, and then corrected to an Aviation number using a 
table in the method - it's usually only 1 - 2 Octane units different to 
the 
Motor value up to 100, but varies significant above that eg 110MON = 
128AN.

The second Avgas number is the Rich Mixture method Performance Number ( 
PN 
- they are not commonly called octane numbers when they are above 100 ), 
and 
is determined on a supercharged version of the CFR engine which has a 
fixed 
compression ratio. The method determines the dependence of the highest 
permissible power ( in terms of indicated mean effective pressure ) on 
mixture strength and boost for a specific light knocking setting. The 
Performance Number indicates the maximum knock-free power obtainable 
from a 
fuel compared to iso-octane = 100. Thus, a PN = 150 indicates that an 
engine
designed to utilise the fuel can obtain 150% of the knock-limited power 
of 
iso-octane at the same mixture ratio. This is an arbitrary scale based 
on 
iso-octane + varying amounts of TEL, derived from a survey of engines 
performed decades ago. Aviation gasoline PNs are rated using variations 
of 
mixture strength to obtain the maximum knock-limited power in a 
supercharged
engine. This can be extended to provide mixture response curves which 
define
the maximum boost ( rich - about 11:1 stoichiometry ) and minimum boost 
( weak about 16:1 stoichiometry ) before knock [94].

The 115/145 grade is being phased out, but even the 100LL has more 
octane 
than any automotive gasoline. 

6.20 Can mothballs increase octane? 

The legend of mothballs as an octane enhancer arose well before WWII 
when
naphthalene was used as the active ingredient. Today, the majority of 
mothballs use para-dichlorobenzene in place of naphthalene, so choose 
carefully if you wish to experiment :-). There have been some concerns 
about 
the toxicity of para-dichlorobenzene, and naphthalene mothballs have 
again
become popular. In the 1920s, typical gasoline octane ratings were 40-60 
[10], and during the 1930s and 40s, the ratings increased by 
approximately 20 
units as alkyl leads and improved refining processes became widespread. 

Naphthalene has a blending motor octane number of 90 [40], so the 
addition of 
a significant amount of mothballs could increase the octane, and they 
were 
soluble in gasoline. The amount usually required to appreciably increase 
the 
octane also had some adverse effects. The most obvious was due to the 
high 
melting point ( 80C ), when the fuel evaporated the naphthalene would 
precipitate out, blocking jets and filters. With modern gasolines, 
naphthalene is more likely to reduce the octane rating, and the amount 
required for low octane fuels will also create operational and emissions 
problems. 

------------------------------


7.1  What is the effect of Compression ratio?

Most people know that an increase in Compression Ratio will require an
increase in fuel octane for the same engine design. Increasing the 
compression ratio increases the theoretical thermodynamic efficiency of 
an 
engine according to the standard equation

Efficiency = 1 - (1/compression ratio)^gamma-1

where gamma = ratio of specific heats at constant pressure and constant 
volume of the working fluid ( for most purposes air is the working 
fluid, 
and is treated as an ideal gas ). There are indications that thermal 
efficiency reaches a maximum at a compression ratio of about 17:1 [16].

The efficiency gains are best when the engine is at incipient knock, 
that's 
why knock sensors ( actually vibration sensors ) are used. Low 
compression 
ratio engines are less efficient because they can not deliver as much of 
the 
ideal combustion power to the flywheel. For a typical carburetted 
engine, 
without engine management [20,30]:-

   Compression       Octane Number    Brake Thermal Efficiency       
     Ratio            Requirement         ( Full Throttle )
      5:1                 72                      -
      6:1                 81                     25 %
      7:1                 87                     28 %
      8:1                 92                     30 %
      9:1                 96                     32 %
     10:1                100                     33 %
     11:1                104                     34 %
     12:1                108                     35 %

Modern engines have improved significantly on this, and the changing 
fuel 
specifications and engine design should see more improvements, but 
significant gains may have to await improved engine materials and fuels.

7.2  What is the effect of changing the air/fuel ratio?

Traditionally, the greatest tendency to knock was near 13.5:1 air/fuel 
ratio, but was very engine specific. Modern engines, with engine 
management 
systems, now have their maximum octane requirement near to 14.5:1. For a 
given engine using gasoline, the relationship between thermal 
efficiency, 
air/fuel ratio, and power is complex. Stoichiometric combustion ( 
Air/Fuel 
Ratio = 14.7:1 for a typical non-oxygenated gasoline ) is neither 
maximum 
power - which occurs around A/F 12-13:1 (Rich), nor maximum thermal 
efficiency - which occurs around A/F 16-18:1 (Lean). The air-fuel ratio 
is 
controlled at part throttle by a closed loop system using the oxygen 
sensor 
in the exhaust. Conventionally, enrichment for maximum power air/fuel 
ratio 
is used during full throttle operation to reduce knocking while 
providing 
better driveability [30]. If the mixture is weakened, the flame speed is
reduced, consequently less heat is converted to mechanical energy, 
leaving
heat in the cylinder walls and head, potentially inducing knock. It is 
possible to weaken the mixture sufficiently that the flame is still 
present
when the inlet valve opens again, resulting in backfiring.

7.3  What is the effect of changing the ignition timing

The tendency to knock increases as spark advance is increased, eg 2 
degrees 
BTDC requires 91 octane, whereas 14 degrees BTDC requires 96 octane.
If you advance the spark, the flame front starts earlier, and the end 
gases
start forming earlier in the cycle, providing more time for the 
autoigniting  
species to form before the piston reaches the optimum position for power 
delivery, as determined by the normal flame front propagation. It 
becomes a 
race between the flame front and decomposition of the increasingly-
squashed 
end gases. High octane fuels produce end gases that take longer to 
autoignite, so the good flame front reaches and consumes them properly. 

The ignition advance map is partly determined by the fuel the engine is 
intended to use. The timing of the spark is advanced sufficiently to 
ensure 
that the fuel/air mixture burns in such a way that maximum pressure of 
the 
burning charge is about 15-20 degree after TDC. Knock will occur before 
this point, usually in the late compression/early power stroke period.
The engine management system uses ignition timing as one of the major
variables that is adjusted if knock is detected. If very low octane 
fuels
are used ( several octane numbers below the vehicle's requirement at 
optimal 
settings ), both performance and fuel economy will decrease.

The actual Octane Number Requirement depends on the engine design, but 
for
some 1978 vehicles using standard fuels, the following (R+M)/2 Octane 
Requirements were measured. "Standard" is the recommended ignition 
timing 
for the engine, probably a few degrees before Top Dead Centre [30].
            
                          Basic Ignition Timing
Vehicle   Retarded 5 degrees    Standard     Advanced 5 degrees
  A              88                91               93
  B              86                90.5             94.5
  C              85.5              88               90
  D              84                87.5             91
  E              82.5              87               90                      

The actual ignition timing to achieve the maximum pressure from normal 
combustion of gasoline will depend mainly on the speed of the engine and 
the 
flame propagation rates in the engine. Knock increases the rate of the 
pressure rise, thus superimposing additional pressure on the normal 
combustion pressure rise. The knock actually rapidly resonates around 
the 
chamber, creating a series of abnormal sharp spikes on the pressure 
diagram. 
The normal flame speed is fairly consistent for most gasoline HCs, 
regardless
of octane rating, but the flame speed is affected by stoichiometry. Note 
that
the flame speeds in this FAQ are not the actual engine flame speeds. A 
12:1
CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 
m/s, 
and a similar hydrogen engine yields 48.3 m/s, but such engine flame 
speeds 
are also very dependent on stoichiometry.  

7.4  What is the effect of engine management systems?

Engine management systems are now an important part of the strategy to 
reduce automotive pollution. The good news for the consumer is their 
ability 
to maintain the efficiency of gasoline combustion, thus improving fuel 
economy. The bad news is their tendency to hinder tuning for power. A 
very 
basic modern engine system could monitor and control:- mass air flow, 
fuel 
flow, ignition timing, exhaust oxygen ( lambda oxygen sensor ), knock 
( vibration sensor ), EGR, exhaust gas temperature, coolant temperature, 
and 
intake air temperature. The knock sensor can be either a nonresonant 
type 
installed in the engine block and capable of measuring a wide range of 
knock 
vibrations ( 5-15 kHz ) with minimal change in frequency, or a resonant 
type 
that has excellent signal-to-noise ratio between 1000 and 5000 rpm [95]. 

A modern engine management system can compensate for altitude, ambient 
air 
temperature, and fuel octane. The management system will also control 
cold 
start settings, and other operational parameters. There is a new 
requirement 
that the engine management system also contain an on-board diagnostic 
function that warns of malfunctions such as engine misfire, exhaust 
catalyst 
failure, and evaporative emissions failure. The use of fuels with 
alcohols 
such as methanol can confuse the engine management system as they 
generate 
more hydrogen which can fool the oxygen sensor [60] .

The use of fuel of too low octane can actually result in both a loss of 
fuel 
economy and power, as the management system may have to move the engine 
settings to a less efficient part of the performance map. The system 
retards 
the ignition timing until only trace knock is detected, as engine damage 
from knock is of more consequence than power and fuel economy. 

7.5  What is the effect of temperature and load?  

Increasing the engine temperature, particularly the air/fuel charge 
temperature, increases the tendency to knock. The Sensitivity of a fuel 
can 
indicate how it is affected by charge temperature variations. Increasing 
load increases both the engine temperature, and the end-gas pressure, 
thus 
the likelihood of knock increases as load increases.

7.6  What is the effect of engine speed?.

Faster engine speed means there is less time for the pre-flame reactions 
in the end gases to occur, thus reducing the tendency to knock. On 
engines
with management systems, the ignition timing may be advanced with engine
speed and load, to obtain optimum efficiency at incipient knock. In such 
cases, both high and low engines speeds may be critical.
          
7.7  What is the effect of engine deposits?

A new engine may only require a fuel of 6-9 octane numbers lower than 
the
same engine after 25,000 km. This Octane Requirement Increase (ORI) is 
due to
the formation of a mixture of organic and inorganic deposits resulting 
from
both the fuel and the lubricant. They reach an equilibrium amount 
because
of flaking, however dramatic changes in driving styles can also result 
in 
dramatic changes of the equilibrium position. When the engine starts to 
burn
more oil, the octane requirement can increase again. ORIs up to 12 are 
not
uncommon, depending on driving style [20,24]. The deposits produce the 
ORI 
by several mechanisms:- 
 - they reduce the combustion chamber volume, effectively increasing the 
   compression ratio. 
 - they also reduce thermal conductivity, thus increasing the combustion 
   chamber temperatures. 
 - they catalyse undesirable pre-flame reactions that produce end gases 
with 
   low autoignition temperatures.  

7.8  What is the Road Octane requirement of an vehicle?

The actual octane requirements of a vehicle is called the Octane Number 
Requirement ( ONR ), and is determined by using standard octane fuels 
that
can be blends of iso-octane and normal heptane, or commercial gasolines. 
The vehicle is tested under a wide range of conditions and loads, using 
different octane fuels until trace knock is detected. The conditions 
that 
require maximum octane are not consistent, but often are full-throttle
acceleration from low starting speeds using the highest gear available. 
They 
can even be at constant speed conditions [20]. Engine management systems 
that adjust the octane requirement may also reduce the power output on 
low 
octane fuel, resulting in increased fuel consumption. The maximum ONR is 
of 
most interest, as that usually defines the recommended fuel.
   
The octane rating engines do not reflect actual conditions in a vehicle,
consequently there are standard procedures for evaluating the 
performance 
of the gasoline in an engine. The most common are:-
1. The Modified Uniontown Procedure. Full throttle accelerations are 
made 

_
  

   from low speed using primary reference fuels. The ignition timing is 
   adjusted until trace knock is detected at some stage. Several 
reference 
   fuels are used, and a Road Octane Number v Basic Ignition timing 
graph is 
   obtained. The fuel sample is tested, and the ignition timing setting 
is 
   read from the graph to provide the Road Octane Number. This is a 
rapid 
   procedure but provides minimal information.
2. The Modified Borderline Knock Procedure. The automatic spark advance 
is
   disabled, and a manual adjustment facility added. Accelerations are 
   performed as in the Modified Uniontown Procedure, however trace knock 
is 
   maintained throughout the run. A map of ignition advance v engine 
speed
   is made for several reference fuels and the sample fuels. This 
procedure
   can show the variation of road octane with engine speed. 
       
7.9  What is the effect of air temperature?
          
An increase in ambient air temperature of 5.6C increases the octane 
requirement of an engine by 0.44 - 0.54 MON [20,30]. When the combined 
effects

of air temperature and humidity are considered, it is often possible to 
use 
one octane grade in summer, and use a lower octane rating in winter. The 
Motor octane rating has a higher charge temperature, and increasing 
charge 
temperature increases the tendency to knock, so fuels with low 
Sensitivity 
( the difference between RON and MON numbers ) are less affected by air 
temperature.

7.10  What is the effect of altitude?

The effect of increasing altitude may be nonlinear, with one study 
reporting 
a decrease of the octane requirement of 1.4 RON/300m from sea level to 
1800m
and 2.5 RON/300m from 1800m to 3600m [20]. Other studies report the 
octane 
number requirement decreased by 1.0 - 1.9 RON/300m without specifying 
altitude [30]. Modern engine management systems can accommodate this 
adjustment, and in some recent studies, the octane number requirement 
was 
0.2 - 0.5 Antiknock Index/300m. The reduction on older engines was due 
to:-
 - reduced air density provides lower combustion temperature and 
pressure.

 - fuel is metered according to air volume, consequently as density 
decreases
   the stoichiometry moves to rich, with a lower octane number 
requirement.
 - manifold vacuum controlled spark advance, and reduced manifold vacuum 
   results in less spark advance.

7.11  What is the effect of humidity?.

An increase of absolute humidity of 1.0 g water/ kg of dry air lowers 
the 
octane requirement of an engine by 0.25 - 0.32 MON [20,30].

7.12  What does water injection achieve?.

Water injection, as a separate liquid or emulsion with gasoline, or as a
vapour, has been thoroughly researched. If engines can calibrated to 
operate 
with small amounts of water, knock can be suppressed, hydrocarbon 
emissions 
will slightly increase, NOx emissions will decrease, CO does not change
significantly, and fuel and energy consumption are increased [96].

Water injection was used in WWII aviation engine to provide a large 
increase 
in available power for very short periods. The injection of water does 
decrease the dew point of the exhaust gases. This has potential 
corrosion 
problems. The very high specific heat and heat of vaporisation of water 
means that the combustion temperature will decrease. It has been shown 
that 
a 10% water addition to methanol reduces the power and efficiency by 
about 
3%, and doubles the unburnt fuel emissions, but does reduce NOx by 25% 
[97]. 
A decrease in combustion temperature will reduce the theoretical maximum 
possible efficiency of an otto cycle engine that is operating correctly, 
but may improve efficiency in engines that are experiencing abnormal 
combustion on existing fuels. 

Some aviation SI engines still use boost fluids. The water/methanol 
mixtures 
are used to provide increased power for short periods, up to 40% more - 
assuming adequate mechanical strength of the engine. The 40/60 or 45/55 
water/methanol mixtures are used as boost fluids for aviation engines 
because 
water would freeze. Methanol is just "preburnt" methane, consequently it 
only 
has about half the energy content of gasoline, but it does have a higher 
heat
of vaporisation, which has a significant cooling effect on the charge. 
Water/methanol blends are more cost-effective than gasoline for 
combustion 
cooling. The high Sensitivity of alcohol fuels has to be considered in 
the 
engine design and settings.

Boost fluids are used because they are far more economical than using 
the 
fuel. When a supercharged engine has to be operated at high boost, the 
mixture has to be enriched to keep the engine operating without knock. 
The 
extra fuel cools the cylinder walls and the charge, thus delaying the 
onset 
of knock which would otherwise occur at the associated higher 
temperatures.

The overall effect of boost fluid injection is to permit a considerable 
increase in knock-free engine power for the same combustion chamber 
temperature. The power increase is obtained from the higher allowable 
boost. 
In practice, the fuel mixture is usually weakened when using boost fluid 
injection, and the ratio of the two fuel fluids is approximately 100 
parts 
of avgas to 25 parts of boost fluid. With that ratio, the resulting 
performance corresponds to an effective uprating of the fuel of about 
25%, 
irrespective of its original value. Trying to increase power boosting 
above 
40% is difficult, as the engine can drown because of excessive liquid 
[94].

Note that for water injection to provide useful power gains, the engine 
management and fuel systems must be able to monitor the knock and adjust 
both stoichiometry and ignition to obtain significant benefits. Aviation 
engines are designed to accommodate water injection, most automobile 
engines 
are not. Returns on investment are usually harder to achieve on engines 
that 
do not normal extend their performance envelope into those regions. 
Water 
injection has been used by some engine manufacturers - usually as an 
expedient way to maintain acceptable power after regulatory emissions 
baggage was added to the engine, but usually the manufacturer quickly 
produces a modified engine that does not require water injection.

------------------------------
        
          
8.1  What causes an empty fuel tank?

* You forgot to refill it.
* Your friendly neighbourhood thief "borrowed" the gasoline - the 
unfriendly 
  one took the vehicle. 
* The fuel tank leaked. 
* Your darling child/wife/husband/partner/mother/father used the car.
* The most likely reason is that your local garage switched to an 
oxygenated 
  gasoline, and the engine management system compensated for the oxygen
  content, causing the fuel consumption to increase significantly.

8.2  Is knock the only abnormal combustion problem?                  

No. Many of the abnormal combustion problems are induced by the same 
conditions, and so one can lead to another.

Preignition occurs when the air/fuel mixture is ignited prematurely by 
glowing deposits or hot surfaces - such as exhaust valves and spark 
plugs. 
If it continues, it can increase in severity and become Run-away Surface 
Ignition (RSI) which prevents the combustion heat being converted into 
mechanical energy, thus rapidly melting pistons. The Ricardo method uses 
an 
electrically-heated wire in the engine to measure preignition tendency. 
The 
scale uses iso-octane as 100 and cyclohexane as 0. 
Some common fuel components:-
             paraffins       50-100
             benzene           26  
             toluene           93
             xylene          >100
             cyclopentane      70
             di-isobutylene    64
             hexene-2         -26

There is no direct correlation between anti-knock ability and 
preignition
tendency, however high combustion chamber temperatures favour both, and 
so 
one may lead to the other. An engine knocking during high-speed 
operation 
will increase in temperature and that can induce preignition, and 
conversely 
any preignition will result in higher temperatures than may induce 
knock.

Misfire is commonly caused by either a failure in the ignition system, 
or
fouling of the spark plug by deposits. The most common cause of deposits
was the alkyl lead additives in gasoline, and the yellow glaze of 
various 
lead salts was used by mechanics to assess engine tune. From the upper 
recess to the tip, the composition changed, but typical compounds ( 
going 
from cold to hot ) were PbClBr; 2PbO.PbClBr; PbO.PbSO4; 
3Pb3(PO4)2.PbClBr.
  
Run-on is the tendency of an engine to continue running after the 
ignition 
has been switched off. It is usually caused by the spontaneous ignition 
of 
the fuel/air mixture, rather than by surface ignition from hotspots or 
deposits, as commonly believed. The narrow range of conditions for 
spontaneous ignition of the fuel/air mixture ( engine speed, charge 
temperature, cylinder pressure ) may be created when the engine is 
switched 
off. The engine may refire, thus taking the conditions out of the 
critical 
range for a couple of cycles, and then refire again, until overall 
cooling 
of the engine drops it out of the critical region. The octane rating of 
the 
fuel is the appropriate parameter, and it is not rare for an engine to 
require a higher Octane fuel to prevent run-on than to avoid knock [20].   
            
8.3  Can I prevent carburetter icing?
          
Yes, carburettor icing is caused by the combination of highly volatile 
fuel, 
high humidity and low ambient temperature. The extent of cooling, caused 
by 
the latent heat of the vaporised gasoline in the carburettor, can be as 
much 
as 20C, perhaps dropping below the dew point of the charge. If this 
happens, 
water will condense on the cooler carburettor surfaces, and will freeze 
if 
the temperature is low enough. The fuel volatility can not always be 
reduced 
to eliminate icing, so anti-icing additives are used.

Two types of additive are added to gasoline to inhibit icing:- 
- surfactants that form a monomolecular layer over the metal parts that 
  inhibits ice crystal formation. These are usually added at 
concentrations 
  of 30-150 ppm.
- cryoscopic additives that depress the freezing point of the condensed 
water 
  so that it does not turn to ice. Alcohols ( methanol, ethanol, iso-
propanol,

  etc. ) and glycols ( hexylene glycol, dipropylene glycol ) are used at 
  concentrations of 0.03% - 1%.

If you have icing problems, the addition of 100-200mls of methanol to a 
full 
tank of dry gasoline will prevent icing under most conditions. If you 
believe
there is a small amount of water in the fuel tank, add 500mls of 
isopropanol 
as the first treatment. Oxygenated gasolines using alcohols can also be 
used.
   
8.4  Should I store fuel to avoid the oxygenate season?

No. The fuel will be from a different season, and will have 
significantly
different volatility properties that may induce driveability problems. 
You 
can tune your engine to perform on oxygenated gasoline as well as it did 
on 
traditional gasoline, however you will have increased fuel consumption 
due 
to the useless oxygen in the oxygenates. Some engines may not initially 
perform well on some oxygenated fuels, usually because of the slightly
different volatility and combustion characteristics. A good mechanic 
should 
be able to recover any lost performance or driveability, providing the 
engine
is in reasonable condition. 
          
8.5  Can I improve fuel economy by using quality gasolines?

Yes, several manufacturers have demonstrated that their new gasoline 
additive
packages are more effective than traditional gasoline formulations. 
Texaco 
claim their new vapour phase fuel additive can reduce existing deposits 
by 
up to 30%, improve fuel economy, and reduce NOx tailpipe emissions by 
15%, 
when compared to other advanced liquid phase additives. These claims 
appear 
to have been verified in independent tests [38]. Other reputable 
gasoline 
brands will have similar additive packages in their quality products 
[39]. 
Quality gasolines, of whatever octane ratings, will include a full range 
of 
gasoline additives designed to provide consistent fuel quality.

Note that oxygenated gasolines must decrease fuel economy for the same 
power.
If your engine is initially well-tuned on hydrocarbon gasolines, the 
stoichiometry will move to lean, and maximum power is slightly rich, so
either the management system ( if you have one ) or your mechanic has to 
increase the fuel flow. The minor improvements in combustion efficiency 
that
oxygenates may provide, can not compensate for 2+% of oxygen in the fuel 
that will not provide energy.         

8.6  What is "stale" fuel, and should I use it?

"Stale" fuel is caused by improper storage, and usually smells sour. The 
gasoline has been allowed to get warm, thus catalysing olefin 
decomposition 
reactions, and perhaps also losing volatile material in unsealed 
containers. 
Such fuel will tend to rapidly form gums, and will usually have a 
significant 
reduction in octane rating. The fuel can be used by blending with twice 
the 
volume of new gasoline. Some stale fuels can drop several octane 
numbers, so
be generous with the dilution.
               
8.7  How can I remove water in the fuel tank?

If you only have a small quantity of water, then the addition of 500mls 
of 
dry isopropanol (IPA) to a near-full 30-40 litre tank will absorb the 
water,
and will not significantly affect combustion. Once you have mopped up 
the 
water with IPA, small, regular doses of any anhydrous alcohol will help 
keep the tank dry. This technique will not work if you have very large 
amounts of water, and the addition of greater amounts of IPA may result 
in 
poor driveability. 

Water in fuel tanks can be minimised by keeping the fuel tank near full, 
and 
filling in the morning from a service station that allows storage tanks 
to 
stand for several hours after refilling before using the fuel. Note that 
oxygenated gasolines have greater water solubility, and should cope with 
small quantities of water.

8.8  Can I used unleaded on older vehicles?

Yes, providing the octane is appropriate. There are some older engines 
that 
cut the valve seats directly into the cylinder head ( eg BMC minis ). 
The 
absence of lead, which lubricated the valve seat, causes the very hard 
oxidation products of the valve to wear down the seat. This valve seat 
recession is usually corrected by installing seat inserts. Most other
problems arise because the fuels have different volatility, or the 
reduction
of combustion chamber deposits. These can usually be cured by reference 
to 
the vehicle manufacturer, who will probably have a publication with the 
changes. Some vehicles will perform as well on unleaded with a slightly 
lower octane than recommended leaded fuel, due to the significant 
reduction 
in deposits from modern unleaded gasolines.   

8.9  How serious is valve seat recession on older vehicles?

The amount of valve seat recession is very dependent on the load on the
engine. There have been several major studies on valve seat recession 
and
they conclude that most damage occurs under high-speed, high-power 
conditions. Engine load is not a primary factor in valve seat wear for 
moderate operating conditions, and low to medium speed engines under 
moderate loads do not suffer rapid recession, as has been demonstrated
on fuels such as CNG and LPG. Under severe conditions, damage occurs 
rapidly, 
however there are significant cylinder-to-cylinder variations on the 
same 
engine. A 1970 engine operated at 70 mph conditions exhibited an average 
1.5mm of seat recession in 12,000km. The difference between cylinders 
has 
been attributed to different rates of valve rotation, and experiments 
have 
confirmed that more rotation does increase the recession rate [21]. 
The mechanism of valve seat wear is a mixture of two major mechanisms. 
Iron 
oxide from the combustion chamber surfaces adheres to the valve face and 
becomes embedded. These hard particles then allow the valve act as a 
grinding
wheel and cut into the valve seat [98]. The significance of valve seat
recession is that should it occur to the extent that the valve does not 
seat,
serious engine damage can result from the localised hot spot.

There are a range of additives, usually based on potassium, sodium or
phosphorus that can be added to the gasoline to combat valve seat 
recession.
As phosphorus has adverse effects on exhaust catalysts, it is seldom 
used.
The best long term solution is to induction harden the seats or install
inserts, usually when the head is removed for other work, however 
additives 
are routinely and successfully used during transition periods.

------------------------------



                          

zephyr.grace.cri.nz!usenet



Archive-name: autos/gasoline-faq/part4

Section: 9. Alternative Fuels and Additives
          
9.1  Do fuel additives work?

Most aftermarket fuel additives are not cost-effective. These include 
the
octane-enhancer solutions discussed in section 6.18. There are various 
other
pills, tablets, magnets, filters, etc. that all claim to improve either 
fuel 
economy or performance. Some of these have perfectly sound scientific
mechanisms, unfortunately they are not cost-effective. Some do not even 
have
sound scientific mechanisms. Because the same model production vehicles 
can 
vary significantly, it's expensive to unambiguously demonstrate these 
additives are not cost-effective. If you wish to try them, remember the
biggest gain is likely to be caused by the lower mass of your 
wallet/purse.

There is one aftermarket additive that may be cost-effective, the 
lubricity 
additive used with unleaded gasolines to combat valve seat recession on 
engines that do not have seat inserts. This additive is now often 
routinely
added during the first few years of unleaded by the gasoline producers. 
The
amount of recession is very dependent on the engine design and driving 
style.
The long-term solution is to install inserts at the next top overhaul. 

Some other fuel additives work, especially those that are carefully 
formulated into the gasoline by the manufacturer at the refinery. 
A typical gasoline may contain [20,24,30]:-
* Oil-soluble Dye, initially added to leaded gasoline at about 10 ppm to 
        prevent its misuse as an industrial solvent 
* Antioxidants, typically phenylene diamines or hindered phenols, are
        added to prevent oxidation of unsaturated hydrocarbons.
* Metal Deactivators, typically about 10ppm of chelating agent such as 
        N,N'-disalicylidene-1,2-propanediamine is added to inhibit 
copper,
        which can rapidly catalyze oxidation of unsaturated 
hydrocarbons.
* Corrosion Inhibitors, about 5ppm of oil-soluble surfactants are added
        to prevent corrosion caused either by water condensing from 
cooling,
        water-saturated gasoline, or from condensation from air onto the 
        walls of almost-empty gasoline tanks that drop below the dew 
point.
        If your gasoline travels along a pipeline, it's possible the 
pipeline
        owner will add additional corrosion inhibitor to the fuel.
* Anti-icing Additives, used mainly with carburetted cars, and usually 
either
        a surfactant, alcohol or glycol.
* Anti-wear Additives, these are used to control wear in the upper 
cylinder
        and piston ring area that the gasoline contacts, and are usually
        very light hydrocarbon oils. Phosphorus additives can also be 
used 
        on engines without exhaust catalyst systems.
* Deposit-modifying Additives, usually surfactants. 
  1. Carburettor Deposits, additives to prevent these were required when 
        crankcase blow-by (PCV) and exhaust gas recirculation (EGR) 
controls
        were introduced. Some fuel components reacted with these gas 
streams 
        to form deposits on the throat and throttle plate of 
carburettors.
  2. Fuel Injector tips operate about 100C, and deposits form in the
        annulus during hot soak, mainly from the oxidation and 
polymerisation
        of the larger unsaturated hydrocarbons. The additives that 
prevent
        and unclog these tips are usually polybutene succinimides or 
        polyether amines.
  3. Intake Valve Deposits caused major problems in the mid-1980s when
        some engines had reduced driveability when fully warmed, even 
though
        the amount of deposit was below previously acceptable limits. It 
is
        believed that the new fuels and engine designs were producing a 
more
        absorbent deposit that grabbed some passing fuel vapour, causing 
lean
        hesitation. Intake valves operate about 300C, and if the valve 
is
        is kept wet deposits tend not to form, thus intermittent 
injectors
        tend to promote deposits. Oil leaking through the valve guides 
can be
        either harmful or beneficial, depending on the type and 
quantity.
        Gasoline factors implicated in these deposits include 
unsaturates and
        alcohols. Additives to prevent these deposits contain a 
detergent
        and/or dispersant in a higher molecular weight solvent or light 
oil
        whose low volatility keeps the valve surface wetted.
  4. Combustion Chamber Deposits have been targeted in the 1990s, as 
they
        are responsible for significant increases in emissions. Recent
        detergent-dispersant additives have the ability to function in 
both
        the liquid and vapour phases to remove existing carbon and 
prevent
        deposit formation.                
* Octane Enhancers, these are usually formulated blends of alkyl lead 
        or MMT compounds in a solvent such as toluene, and added at the
        100-1000  ppm levels. They have been replaced by hydrocarbons 
with
        higher octanes such as aromatics and olefins. These hydrocarbons
        are now being replaced by a mixture of saturated hydrocarbons 
and
        and oxygenates.

If you wish to play with different fuels and additives, be aware that
some parts of your engine management systems, such as the oxygen sensor, 
can be confused by different exhaust gas compositions. An example is 
increased quantities of hydrogen from methanol combustion.

9.2  Can a quality fuel help a sick engine?
          
It depends on the ailment. Nothing can compensate for poor tuning and 
wear.
If the problem is caused by deposits or combustion quality, then modern 
premium quality gasolines have been shown to improve engine performance 
significantly. The new generation of additive packages for gasolines 
include 
components that will dissolve existing carbon deposits, and have been 
shown 
to improve fuel economy, NOx emissions, and driveability.

9.3  What are the advantages of alcohols and ethers?

This section discusses only the use of high ( >80% ) alcohol or ether 
fuels.

Alcohol fuels can be made from sources other than imported crude oil, 
and the
nations that have researched/used alcohol fuels have mainly based their 
choice on import substitution. Alcohol fuels can burn more efficiently, 
and 
can reduce photochemically-active emissions. Most vehicle manufacturers 
favoured the use of liquid fuels over compressed or liquified gases. The 
alcohol fuels have high research octane ratings, but also high 
sensitivity 
and high latent heats [7,20,64,99]. 
                                Methanol       Ethanol     Unleaded 
Gasoline
RON                               106            107           92 - 98
MON                                92             89           80 - 90
Heat of Vaporisation    (MJ/kg)     1.154          0.913        0.3044
Nett Heating Value      (MJ/kg)    19.95          26.68        42 - 44
Vapour Pressure @ 38C    (kPa)     31.9           16.0         48 - 108
Flame Temperature        ( C )   1870           1920          2030 
Stoich. Flame Speed.    ( m/s )     0.43           -             0.34
Minimum Ignition Energy ( mJ )      0.14           -             0.29
Lower Flammable Limit   ( vol% )    6.7            3.3           1.3          

Upper Flammable Limit   ( vol% )   36.0           19.0           7.1
Autoignition Temperature ( C )    460            360          260 - 460     
Flash Point              ( C )     11             13          -43 - -39
    
The major advantages are gained when pure fuels ( M100, and E100 ) are 
used,
as the addition of hydrocarbons to overcome the cold start problems also
significantly reduces, if not totally eliminates, any emission benefits.
Methanol will produce significant amounts of formaldehyde, a suspected
human carcinogen, until the exhaust catalyst reaches operating 
temperature.
Ethanol produces acetaldehyde. The cold-start problems have been 
addressed, 
and alcohol fuels are technically viable, however with crude oil at 
<$30/bbl they are not economically viable, especially as the demand for 
then 
as precursors for gasoline oxygenates has elevated the world prices. 
Methanol almost doubled in price during 1994. There have also been 
trials
of pure MTBE as a fuel, however there are no unique or significant 
advantages
that would outweigh the poor economic viability [12]. 

9.4  Why are CNG and LPG considered "cleaner" fuels.
          
CNG ( Compressed Natural Gas ) is usually around 70-90% methane with 10-
20% 
ethane, 2-8% propanes, and decreasing quantities of the higher HCs up to 
butane. The fuel has a high octane and usually only trace quantities of 
unsaturates. The emissions from CNG have lower concentrations of the 
hydrocarbons responsible for photochemical smog, reduced CO, SOx, and 
NOx, 
and the lean misfire limit is extended [100]. There are no technical
disadvantages, providing the installation is performed correctly. The 
major 
disadvantage of compressed gas is the reduced range. Vehicles may have
between one to three cylinders ( 25 MPa, 90-120 litre capacity), and 
they 
usually represent about 50% of the gasoline range. As natural gas 
pipelines
do not go everywhere, most conversions are dual-fuel with gasoline. The 
ignition timing and stoichiometry are significantly different, but good
conversions will provide about 85% of the gasoline power over the full
operating range, with easy switching between the two fuels [101]. 
Concerns
about the safety of CNG have proved to be unfounded [102].  

CNG has been extensively used in Italy and New Zealand ( NZ had 130,000 
dual-fuelled vehicles with 380 refuelling stations in 1987 ). The 
conversion 
costs are usually around US$1000, so the economics are very dependent on 
the
natural gas price. The typical 15% power loss means that driveability of 
retrofitted CNG-fuelled vehicles is easily impaired, consequently it is 
not 
recommended for vehicles of less than 1.5l engine capacity, or 
retrofitted 
onto engine/vehicle combinations that have marginal driveability on 
gasoline.
The low price of crude oil, along with installation and ongoing CNG 
tank-testing costs, have reduced the number of CNG vehicles in NZ. The 
US
CNG fleet continues to increase in size ( 60,000 in 1994 ). 
 
LPG ( Liquified Petroleum Gas ) is predominantly propane with iso-butane
and n-butane. It has one major advantage over CNG, the tanks do not have
to be high pressure, and the fuel is stored as a liquid. The fuel offers   
most of the environmental benefits of CNG, including high octane. 
Approximately 20-25% more fuel is required, unless the engine is 
optimised 
( CR 12:1 ) for LPG, in which case there is no decrease in power or 
increase
in fuel consumption [20,101]. There have been several studies that have
compared the relative advantages of CNG and LPG, and often LPG has been
found to be a more suitable transportation fuel [102].

                                  methane        propane        iso-
octane    

RON                                 120            112           100
MON                                 120             97           100
Heat of Vaporisation    (MJ/kg)       0.5094         0.4253        
0.2712
Net Heating Value       (MJ/kg)      50.0           46.2          44.2
Vapour Pressure @ 38C   ( kPa )       -               -           11.8
Flame Temperature        ( C )     1950           1925          1980
Stoich. Flame Speed.    ( m/s  )      0.45           0.45          0.31
Minimum Ignition Energy  ( mJ )       0.30           0.26           -
Lower Flammable Limit   ( vol% )      5.0            2.1           0.95

Upper Flammable Limit   ( vol% )     15.0            9.5           6.0
Autoignition Temperature  ( C )    540 - 630       450           415       

9.5  Why are hydrogen-powered cars not available?

The Hindenburg.

The technology to operate IC engines on hydrogen has been investigated 
in 
depth since before the turn of the century. One attraction was to
use the hydrogen in airships to fuel the engines instead of venting it.
Hydrogen has a very high flame speed ( 3.24 - 4.40 m/s ), wide 
flammability 
limits ( 4.0 - 75 vol% ), low ignition energy ( 0.017 mJ ), high 
autoignition 
temperature ( 520C ), and flame temperature of 2050 C. Hydrogen has a 
very 
high specific energy ( 120.0 MJ/kg ), making it very desirable as a 
transportation fuel.  The problem has been to develop a storage system 
that 
will pass all safety concerns, and yet still be light enough for 
automotive 
use. Although hydrogen can be mixed with oxygen and combusted more
efficiently, most proposals use air [97,102,104-107].

Unfortunately the flame temperature is sufficiently high to dissociate 
atmospheric nitrogen and form undesirable NOx emissions. The high flame 
speeds mean that ignition timing is at TDC, except when running lean, 
when
the ignition timing is advanced 10 degrees. The high flame speed, 
coupled
with a very small quenching distance mean that the flame can sneak past
inlet narrow inlet valve openings and cause backflash. This can be 
mitigated by the induction of fine mist of water, which also has the 
benefit of increasing thermal efficiency ( although the water lowers the
combustion temperature, the phase change creases voluminous gases that
increase pressure ) and reducing NOx [107]. An alternative technique is
to use direct cylinder induction, which injects hydrogen once the 
cylinder
has filled with an air charge, and because the volume required is so
large, modern engines have two inlet valves, one for hydrogen and one 
for
air [107]. The advantage of a wide range of mixture strengths and high 
thermal efficiencies are matched by the disadvantages of pre-ignition 
and 
knock unless weak mixtures, clean engines, and cool operation are used.  

Interested readers are referred to the group sci.energy.hydrogen and the
" Hydrogen Energy" monograph in the Kirk Othmer Encyclopedia of Chemical
Technology [107], for recent information about this fuel. 

9.6  What are "fuel cells" ?
          
Fuel cells are electrochemical cells that directly oxidise the fuel at 
electrodes producing electrical and thermal energy. The oxidant is 
usually 
oxygen from the air and the fuel is usually gaseous, with hydrogen 
preferred. There has, so far, been little success using low temperature 
fuel 
cells ( < 200C ) to perform the direct oxidation of hydrocarbon-based 
liquids
or gases. Methanol can be used as a source for the hydrogen by adding an 
on-board reformer. The main advantage of fuel cells is their high fuel-
to- 
electricity efficiency of about 40-60% of the nett calorific value of 
the 
fuel. As fuel cells also produce heat that can be used for vehicle 
climate 
control, fuel cells are the most likely candidate to replace the IC 
engine 
as a primary energy source. Fuel cells are quiet and produce virtually 
no 
toxic emissions, but they do require a clean fuel ( no halogens, CO, S, 
or 
ammonia ) to avoid poisoning. They currently are expensive to produce, 
and 
have a short operational lifetime, when compared to an IC engine [108-
110].

9.7  What is a "hybrid" vehicle?

A hybrid vehicle has three major systems [111].
1. A primary power source, either an IC engine driven generator where 
the 
   IC engine only operates in the most efficient part of it's 
performance 
   map, or alternatives such as fuel cells and turbines.
2. A power storage unit, which can be a flywheel, battery, or 
ultracapacitor.
3. A drive unit, almost always now an electric motor that can used as a 
   generator during braking. Regenerative braking may increase the 
   operational range about 8-13%.

Battery technology has not yet advanced sufficiently to economically 
substitute for an IC engine, while retaining the carrying capacity, 
range, 
performance, and driveability of the vehicle. Hybrid vehicles may enable 
this problem to be at least partially overcome, but they remain 
expensive, 
and the current ZEV proposals exclude fuel cells and hybrids systems, 
but 
this is being re-evaluated.

9.8  What about other alternative fuels?

9.8.1 Ammonia (NH3)

Anhydrous ammonia has been researched because it does not contain any 
carbon,
and so would not release any CO2. The high heat of vaporisation requires
a pre-vaporisation step, preferably also with high jacket temperatures 
( 180C ) to assist decomposition. Power outputs of about 70% of that of
gasoline under the same conditions have been achieved [97].
 
9.8.2 Water

Mr. Gunnerman has been promoting his patents that claim mixing one part 
of
gasoline with 2 parts water can provide as much power from an IC engine 
as 
the same flow rate of gasoline. He claims the increased efficiency is 
from
catalysed dissociation of water to H2 and 02, as the combustion chamber 
of 
the test engine contained a catalyst. It takes the same amount of energy 
to 
dissociate water, as is reclaimed when the H2 and 02 burn. For his fuel 
to 
provide such power, he has to utilise heat energy that is normally lost. 

As water/gasoline fuels have been extensively investigated [96,112],
interested potential investors may wish to refer to those papers for 
some
background. Mr. Gunnerman appears to have modified his claims a little 
with 
his new A55 fuel.  A recent article claims a 29% increase in fuel 
economy 
for a test bus in Reno, but also claims that his fuel combusts so 
efficiently that it can pass an emissions test without requiring a 
catalytic 
converter [113]. Caterpillar are working with Gunnerman to evaluate his 
claims and develop the product.

9.9  What about alternative oxidants?

9.9.1 Nitrous Oxide

Nitrous oxide ( N2O ) contains 33 vol% of oxygen, consequently the 
combustion 
chamber is filled with less useless nitrogen. It is also metered in as a
liquid, which can cool the incoming charge further, thus effectively
increasing the charge density. With all that oxygen, a lot more fuel can
be squashed into the combustion chamber. The advantage of nitrous oxide 
is
that it has a flame speed, when burned with hydrocarbon and alcohol 
fuels, 
that can be handled by current IC engines, consequently the power is 
delivered in an orderly fashion, but rapidly. The same is not true for 
pure oxygen combustion with hydrocarbons, so leave that oxygen cylinder 
on 
the gas axe alone :-). Nitrous oxide has also been readily available at 
a
reasonable price, and is popular as a fast way to increase power in 
racing
engines. The following data are for common premixed flames [114]. 
              
                               Temperature     Flame Speed  
  Fuel         Oxidant            ( C )           ( m/s )            
Acetylene        Air               2400         1.60 - 2.70
   "         Nitrous Oxide         2800             2.60
   "            Oxygen             3140         8.00 - 24.80
Hydrogen         Air               2050         3.24 - 4.40
   "         Nitrous Oxide         2690             3.90
   "            Oxygen             2660         9.00 - 36.80
Propane          Air               1925             0.45
Natural Gas      Air               1950             0.39

Nitrous oxide is not yet routinely used on standard vehicles, but the 
technology is well understood. 

_
                                                                                                        


9.9.2 Membrane Enrichment of Air

Over the last two decades, extensive research has been performed on the
use of membranes to enrich the oxygen content of air. Increasing the 
oxygen
content can make combustion more efficient due to the higher flame 
temperature and less nitrogen. The optimum oxygen concentration for 
existing 
automotive engine materials is around 30 - 40%. There are several 
commercial 
membranes that can provide that level of enrichment. The problem is that 
the 
surface area required to produce the necessary amount of enriched air 
for an 
SI engine is very large. The membranes have to be laid close together, 
or 
wound in a spiral, and significant amounts of power are required to 
force 
the air along the membrane surface for sufficient enriched air to run a
slightly modified engine. Most research to date has centred on CI 
engines, 
with their higher efficiencies. Several systems have been tried on 
research 
engines and vehicles, however the higher NOx emissions remain a problem 
[115,116]. 

------------------------------

        
10.1  The myth of Triptane

[ This post is an edited version of several posts I made after JdA 
posted 
  some claims from a hot-rod enthusiast reporting that triptane + 4cc 
TEL 
  had a rich power octane rating of 270. This was followed by another 
  post that claimed the unleaded octane was 150.]

In WWII there was a major effort to increase the power of the aviation 
engines continuously, rather than just for short periods using boost 
fluids.
Increasing the octane of the fuel had dramatic effects on engines that 
could 
be adjusted to utilise the fuel ( by changing boost pressure ). There 
was a 
12% increase in cruising speed, 40% increase in rate of climb, 20% 
increase 
in ceiling, and 40% increase in payload for a DC-3, if the fuel went 
from 87 
to 100 Octane, and further increases if the engine could handle 100+ PN 
fuel
[117]. A 12 cylinder Allison aircraft engine was operated on a 60% blend 
of
triptane ( 2,2,3-trimethylbutane ) in 100 octane leaded gasoline to 
produce 
2500hp when the rated take-off horsepower with 100 octane leaded was 
1500hp
[11].

Triptane was first shown to have high octane in 1926 as part of the 
General 
Motors Research Laboratories investigations [118]. As further interest 
developed, gallon quantities were made in 1938, and a full size 
production 
plant was completed in late 1943. The fuel was tested, and the high lead 
sensitivity resulted in power outputs up to 4 times that of iso-octane, 
and 
as much as 25% improvement in fuel economy over iso-octane [11]. 

All of this sounds incredibly good, but then, as now, the cost of octane 
enhancement has to be considered, and the plant producing triptane was 
not 
really viable. The fuel was fully evaluated in the aviation test 
engines, 
and it was under the aviation test conditions - where mixture strength 
is 
varied, that the high power levels were observed over a narrow range of 
engine adjustment. If turbine engines had not appeared, then maybe 
triptane 
would have been used as an octane agent in leaded aviation gasolines. 
Significant design changes would have been required for engines to 
utilise 
the high anti-knock rating. 

As an unleaded additive, it was not that much different to other 
isoalkanes, 
consequently the modern manufacturing processes for aviation gasolines 
are 
alkylation of unsaturated C4 HCs with isobutane, to produce a highly 
iso-paraffinic product, and/or aromatization of naphthenic fractions to 
produce aromatic hydrocarbons possessing excellent rich-mixture 
antiknock 
properties.

So, the myth that triptane was the wonder anti-knock agent that would 
provide
heaps of power arose. In reality, it was one of the best of the iso-
alkanes 
( remember we are comparing it to iso-octane which just happened to be 
worse 
than most other iso-alkanes), but it was not _that_ different from other 
members. It was targeted, and produced, for supercharged aviation 
engines
that could adjust their mixture strength, used highly leaded fuel, and 
wanted
short period of high power for takeoff, regardless of economy. 

The blending octane number, which is what we are discussing, of triptane
is designated by the American Petroleum Institute Research Project 45 
survey
as 112 Motor and 112 Research [40]. Triptane does not have a 
significantly 
different blending number for MON or RON, when compared to iso-octane. 
When TEL is added, the lead response of a large number of paraffins is 
well 
above that of iso-octane ( about +45 for 3ml TEL/US Gal ), and this can 
lead 
to Performance Numbers that can not be used in conventional automotive 
engines [11].
    
10.2  From Honda Civic to Formula 1 winner.                    

[ The following is edited from a post in a debate over the advantages of
water injection. I tried to demonstrate what modifications would be 
required 
to convert my own 1500cc Honda Civic into something worthwhile :-).]

There are many variables that will determine the power output of an 
engine. 
High on the list will be the ability of the fuel to burn evenly without 
knock. No matter how clever the engine, the engine power output limit is 
determined by the fuel it is designed to use, not the amount of oxygen 
stuffed into the cylinder and compressed. Modern engines designs and 
gasolines are intended to reduce the emission of undesirable exhaust 
pollutants, consequently engine performance is mainly constrained by the 
fuel available.

My Honda Civic uses 91 RON fuel, but the Honda Formula 1 turbocharged 
1.5 
litre engine was only permitted to operate on 102 Research Octane fuel, 
and
had limits placed on the amount of fuel it could use during a race, the
maximum boost of the turbochargers was specified, as was an additional 
40kg penalty weight. Standard 102 RON gasoline would be about 96 R+M/2 
if 
sold as a pump gasoline. The normally-aspirated 3.0 litre engines could 
use 
unlimited amounts of 102RON fuel. The F1 race duration is 305 km or 2 
hours,
and it's perhaps worth remembering that Indy cars run at 7.3 psi boost.

Engine                 Standard         Formula One     Formula One 
Year                     1986              1987            1989

Size                   1.5 litre         1.5 litre       1.5 litre
Cylinders                 4                 6               6 
Aspiration              normal            turbo           turbo
Maximum Boost             -               58 psi          36.3 psi           
Maximum Fuel              -              200 litres      150 litres  
Fuel                    91 RON           102 RON         102 RON
Horsepower @ rpm      92 @ 6000         994 @ 12000     610 @ 12500
Torque (lb-ft @ rpm)  89 @ 4500         490 @  9750     280 @ 10000
   

Lets consider the transition from Standard to Formula 1, without 
considering
materials etc. 

1. Replace the exhaust system. HP and torque both climb to 100.
2. Double the rpm while improving breathing, you now have 200hp
   but still only about 100lb-ft of torque. 
3. Boost it to 58psi which equals four such engines, so you have 1000hp 
   and 500lb-ft of torque.

Simple?, not with 102 RON fuel, the engine would detonate to pieces. 
so..

4. Lower the compression ratio to 7.4:1, and the higher rpm is a
   big advantage - there is much less time for the end gases to
   ignite and cause detonation.
5. Optimise engine design. 80 degree bank angles V for aerodynamic 
   reasons and go to six cylinders = V-6
6. Cool the air. The compression of 70F air at 14.7psi to 72.7psi
   raises its temperature to 377F. The turbos churn the air and
   although they are about 75% efficient the air is now at 479F.
   The huge intercoolers could reduce the air to 97F, but that 
   was too low to properly vaporise the fuel.
7. Bypass the intercoolers to maintain 104F.
8. Change the Air:Fuel ratio to 23% richer than stoichiometric
   to reduce combustion temperature.
9. Change to 84:16 toluene/heptane fuel, harder to vaporise, but
   complies with the 102 RON requirement 
10.Add sophisticated electronic timing and engine management controls
   to ensure reliable combustion with no detonation.

You now have a six-cylinder, 1.5 litre, 1000hp Honda Civic.

For subsequent years the restrictions were even more severe, 150 litres
and 36.3 maximum boost, in a still vain attempt to give the 3 litre,
normally-aspirated engines a chance. Obviously Honda took advantage
of the reduced boost by increasing CR to 9.4:1, and only going to 15%
rich air/fuel ratio. They then developed an economy mode that involved
heating the liquid fuel to 180F to improve vaporisation, and increased
the air temp to 158F, and leaned out the air-fuel ratio to just 2% rich.
The engine output dropped to 610hp @ 12,500 ( from  685hp @ 12,500 and
about 312 lbs-ft of torque @ 10,000 rpm ), but 32% of the energy in
the fuel was converted to mechanical work. The engine still had crisp
throttle response, and still beat the normally aspirated engines that
did not have the fuel limitation. So turbos were banned. No other
F1 racing engine has ever come close to converting 32% of the fuel
energy into work [119].
                
------------------------------ 

         
11.1  Books and Research Papers
    
   1.  Modern Petroleum Technology - 5th edition.
       Editor, G.D.Hobson.
       Wiley. ISBN 0 471 262498 (1984).
       - Chapter 1. G.D.Hobson.

   2.  Hydrocarbons from Fossil Fuels and their Relationship with Living
       Organisms.
       I.R.Hills, G.W.Smith, and E.V.Whitehead.
       J.Inst.Petrol., v.56 p.127-137 (May 1970).

   3.  Reference 1.
       - Chapter 9. R.E.Banks and P.J.King.

   4.  Ullmann's Encyclopedia of Industrial Chemistry - 5th edition. 
       Editor, B.Elvers.
       VCH. ISBN 3-527-20123-8 (1993).
       - Volume A23. Resources of Oil and Gas.

   5.  BP Statistical Review of World Energy - June 1994.
       - Proved Reserves at end 1993. p.2.
  
   6.  1995 National Assessment of U.S. Oil and Gas Resources.
       U.S. Geological Survey Circular 1118
       U.S. Geological Survey Information Services
       P.O. Box 25286, Federal Center
       Denver, CO 80225

   7.  Kirk-Othmer Encyclopedia of Chemical Technology - 4th edition.
       Editor M.Howe-Grant.
       Wiley. ISBN 0-471-52681-9 (1993-) 
       - Volume 1. Alcohol Fuels.

   8.  Midgley: Saint or Serpent?.
       G.B.Kauffman.
       Chemtech, December 1989. p.717-725.

   9.  ?
       T.Midgley Jr., T.A.Boyd.
       Ind. Eng. Chem., v.14 p.589,849,894 (1922).
 
  10.  Measurement of the Knock Characteristics of Gasoline in terms of 
a
       Standard Fuel.
       G. Edgar.
       Ind. Eng. Chem., v.19 p.145-146 (1927).

  11.  The Effect of the Molecular Structure of Fuels on the Power and 
       Efficiency of Internal Combustion Engines.
       C.F.Kettering.
       Ind. Eng. Chem., v.36 p.1079-1085 (1944).

  12.  Experiments with MTBE-100 as an Automobile Fuel.
       K.Springer, L.Smith.
       Tenth International Symposium on Alcohol Fuels. 
       - Proceedings, v.1 p.53 (1993).
 
  13.  Oxygenates for Reformulated Gasolines.
       W.J.Piel, R.X.Thomas.
       Hydrocarbon Processing, July 1990. p.68-73.

  14.  The Chemical Kinetics of Engine Knock.
       C.K.Westbrook, W.J. Pitz.
       Energy and Technology Review, Feb/Mar 1991. p.1-13. 

  15.  The Chemistry Behind Engine Knock.
       C.K.Westbrook.
       Chemistry & Industry (UK), 3 August 1992. p.562-566.
  
  16.  A New Look at High Compression Engines. 
       D.F.Caris and E.E.Nelson.
       SAE Paper 812A. (1958).

  17.  Problem + Research + Capital = Progress
       T.Midgley,Jr.
       Ind. Eng. Chem., v.31 p.504-506 (1939). 

  18.  Dying for Work: Workers' Safety and Health in 20th Century 
America.
       Edited by D.Rosner & G.Markowitz.
       Indiana University Press. ISBN 0-253-31825-4 (1987).
  
  19.  Tetraethyl Lead Poison Hazards
       T.Midgley,Jr.
       Ind. Eng. Chem., v.17 p.827-828 (1925). 

  20.  Reference 1.
       - Chapter 20. K.Owen.

  21.  Role of Lead Antiknocks in Modern Gasolines.
       A.J.Pahnke and W.E.Bettoney
       SAE Paper 710842 (1971) 32pp.

  22.  Automotive Gasolines - Recommended Practice
       SAE J312 Jan93.
       - Section 3.
       SAE Handbook, volume 1. ISBN 1-56091-461-0 (1994).

  23.  EPA told not to ban Ethyl's fuel additive
       M.Reisch
       Chemical & Engineering News, 24 April 1995 p.8.

  24.  Reference 7.
       - Volume 12. Gasoline and Other Motor Fuels
     
  25.  The Science of Petroleum. Oxford Uni. Press (1938).
       Various editors.
       Section 11. Anti-knock Compounds. v.4. p.3024-3029.
       G. Calingaert.

  26.  Refiners have options to deal with reformulated gasoline.
       G.Yepsin and T.Witoshkin.
       Oil & Gas Journal, 8 April 1991. p.68-71.

  27.  Stoichiometric Air/Fuel Ratios of Automotive Fuels - Recommended
       Practice.
       SAE J1829 May92.
       SAE Handbook, volume 1. ISBN 1-56091-461-0 (1994).  
   
  28.  Chemical Engineers' Handbook - 5th edition
       R.H.Perry and C.H.Chilton.
       McGraw-Hill. ISBN 07-049478-9 (1973)
       - Chapter 3.

  29.  Alternative Fuels
       E.M.Goodger.
       MacMillan. ISBN 0-333-25813-4 (1980)
       - Appendix 4. 

  30.  Automotive Gasolines - Recommended Practice.
       SAE J312 Jan93.
       SAE Handbook, volume 1. ISBN 1-56091-461-0 (1994).

  31.  Standard Specification for Automotive Spark-Ignition Engine Fuel.
       ASTM D 4814-94d.
       Annual Book of ASTM Standards, v.05.03. ISBN 0-8031-2218-7 
(1995).

  32.  Criteria for Quality of Petroleum Products.
       Editor, J.P. Allinson.
       Applied Science. ISBN 0 85334 469 8
       - Chapter 5. K.A.Boldt and S.T.Griffiths.

  33.  Meeting the challenge of reformulated gasoline.
       R.J. Schmidt, P.L.Bogdan, and N.L.Gilsdorf.
       Chemtech, February 1993. p.41-42.

  34.  The Relationship between Gasoline Composition and Vehicle 
Hydrocarbon
       Emissions: A Review of Current Studies and Future Research Needs. 
       D. Schuetzle, W.O.Siegl, T.E.Jensen, M.A.Dearth, E.W.Kaiser, 
R.Gorse,
       W.Kreucher, and E.Kulik.
       Environmental Health Perspectives Supplements v.102 s.4 p.3-12. 
(1994) 

  35.  Reference 29.
       - Chapter 5.

  36.  Intake Valve Deposits: engines, fuels and additive effects
       Automotive Engineering, January 1989. p.49-53.

  37.  Intake Valve Deposits' Impact on emissions.
       Automotive Engineering, February 1993. p.25-29. 

  38.  Texaco to introduce clean burning gasoline.
       Oil & Gas Journal, 28 February 1994. p.22-23.

  39.  Additives to have key role in new gasoline era.
       R.J.Peyla
       Oil & Gas Journal, 11 February 1991. p.53-57.

  40.  Knocking Characteristics of Pure Hydrocarbons.
       ASTM STP 225. (1958)

  41.  Health Effects of Gasoline.
       Environmental Health Perspectives Supplements v.101. s.6 (1993)

  42.  Odor and Health Complaints with Alaskan Gasolines.
       S.L.Smith, L.K.Duffy.
       Chemical Health & Safety, May/June 1995. p.32-38.

  43.  Speciated Measurements and Calculated Reactivities of Vehicle 
Exhaust
       Emissions from Conventional and Reformulated Gasolines.
       S.K.Hoekman.
       Environ. Sci. Technol., v.26 p.1206-1216 (1992).

  44.  Effect of Fuel Structure on Emissions from a Spark-Ignited 
Engine.
       2. Naphthene and Aromatic Fuels.
       E.W.Kaiser, W.O.Siegl, D.F.Cotton, R.W.Anderson.
       Environ. Sci. Technol., v.26 p.1581-1586 (1992). 

  45.  Determination of PCDDs and PCDFs in Car Exhaust.
       A.G.Bingham, C.J.Edmunds, B.W.L.Graham, and M.T.Jones.
       Chemosphere, v.19 p.669-673 (1989).
  
  46.  A New Formula for Fighting Urban Ozone.
       T.Reichhardt.
       Environ. Sci. Technol., v.29 n.1 p.36A-41A (1995).

  47.  Volatile Organic Compounds: Ozone Formation, Alternative Fuels 
and
       Toxics.
       B.J.Finlayson-Pitts and J.N.Pitts Jr..
       Chemistry and Industry (UK), 18 October 1993. p.796-800.

  48.  The rise and rise of global warming.
       R.Matthews.
       New Scientist, 26 November 1994. p.6.       

  49.  Studies Say - Tentatively - That Greenhouse warming is here.
       R.A.Kerr
       Science, v.268. p.1567-1568. (1995)

  50.  Energy-related Carbon Dixode Emissions per Capita for OECD 
Countries
       during 1990.
       International Energy Agency. (1993)

  51.  Market Data Book - 1991, 1992, 1993, 1994 and 1995 editions.
       Automobile News
       - various tables

  52.  BP Statistical Review of World Energy - June 1994.
       - Crude oil consumption p.7.   

  53.  Automotive Gasolines - Recommended Practice
       SAE J312 Jan93.
       - Section 4
       SAE Handbook, volume 1. ISBN 1-56091-461-0 (1994).       

  54.  The Rise and Fall of Lead in Petrol.
       I.D.G.Berwick
       Phys. Technol., v.18 p.158-164 (1987)

  55.  Genotoxic and Carcinogenic Metals: Environmental and Occupational
       Occurance and Exposure.
       Edited by L.Fishbein, A.Furst, M.A.Mehlman.
       Princetown Scientific Publishing. ISBN 0-911131-11-6 (1987)

_
                     

       "Lead" p.211-243.

  56.  E.C. seeks gasoline emission control.  
       Hydrocarbon Processing, September 1990. p.43.

  57.  Health Effects of Gasoline Exposure. I. Exposure assessment for 
U.S.
       Distribution Workers.
       T.J.Smith, S.K.Hammond, and O.Wong.
       Environmental Health Perspectives Supplements. v.101 s.6 p.13 
(1993) 

  58.  Atmospheric Chemistry of Tropospheric Ozone Formation: Scientific 
and
       Regulatory Implications.
       B.J.Finlayson-Pitts and J.N.Pitts, Jr.
       Air & Waste, v.43 p.1091-1100 (1993).

  59.  Trends in Auto Emissions and Gasoline Composition.
       R.F.Sawyer
       Environmental Health Perspectives Supplements. v.101 s.6 p.5 
(1993) 

  60.  Reference 7.
       - Volume 9. Exhaust Control, Automotive.

  61.  Achieving Acceptable Air Quality: Some Reflections on Controlling
       Vehicle Emissions.
       J.G.Calvert, J.B.Heywood, R.F.Sawyer, J.H.Seinfeld 
       Science v261 p37-45 (1993).

  62.  Radiometric Determination of Platinum and Palladium attrition 
from
       Automotive Catalysts.
       R.F.Hill and W.J.Mayer.
       IEEE Trans. Nucl. Sci., NS-24, p.2549-2554 (1977).

  63.  Determination of Platinum Emissions from a three-way 
       catalyst-equipped Gasoline Engine.
       H.P.Konig, R.F.Hertel, W.Koch and G.Rosner.
       Atmospheric Environment, v.26A p.741-745 (1992).

  64.  Alternative Automotive Fuels - SAE Information Report.
       SAE J1297 Mar93.
       SAE Handbook, volume 1. ISBN 1-56091-461-0 (1994).

  65.  Lean-burn Catalyst offers market boom.
       New Scientist, 17 July 1993. p.20.

  66.  Catalysts in cars.
       K.T.Taylor.
       Chemtech, September 1990. p.551-555.

  67.  Advanced Batteries for electric vehicles.
       G.L.Henriksen, W.H.DeLuca, D.R.Vissers.
       Chemtech, November 1994. p.32-38.

  68.  The great battery barrier.
       IEEE Spectrum, November 1992. p.97-101.

  69.  Improving Automobile Efficiency
       J.DeCicco, M.Ross
       Scientific American, December 1994. p.30-35.

  70.  Use market forces to reduce auto pollution.
       W.Harrington, M.A.Walls, V.McConnell.
       Chemtech, May 1995. p.55-60.

  71.  Exposure of the general Population to Gasoline.
       G.G.Akland
       Environmental Health Perspectives Supplements. v.101 s.6 p.27-32 
(1993)

  72.  Court Ruling Spurs Continued Debate Over Gasoline Oxygenates.
       G.Peaff.
       Chemical & Engineering News, 26 September 1994. p.8-13.   

  73.  Court Voids EPA rule on ethanol use in Fuel  
       Chemical & Engineering News, 8 May 1995. p.7-8.

  74.  The Application of Formaldehyde Emission Measurement to the 
       Calibration of Engines using Methanol as a Fuel.
       P.Waring, D.C.Kappatos, M.Galvin, B.Hamilton, and A.Joe.
       Sixth International Symposium on Alcohol Fuels.
       - Proceedings, v.2 p.53-60 (1984).

  75.  Emissions from 200,000 vehicles: a remote sensing study.
       P.L.Guenther, G.A.Bishop, J.E.Peterson, D.H.Stedman.
       Sci. Total Environ., v.146/147 p.297-302 (1994)

  76.  Remote Sensing of Vehicle Exhaust Emissions.
       S.H.Cadle and R.D.Stephens.
       Environ. Sci. Technol., v.28 p.258A-264A. (1994)

  77.  Real-World Vehicle Emissions: A Summary of the Third Annual CRC-
APRAC
       On-Road Vehicle Emissions Workshop.
       S.H.Cadle, R.A.Gorse, D.R.Lawson.
       Air & Waste, v.43 p.1084-1090 (1993)
       
  78.  On-Road Emission Performance of Late-Model TWC-Cars as Measured 
by
       Remote Sensing
       Ake Sjodin
       Air & Waste, v.44 p.397-404 (1994)

  79.  Emission Characteristics of Mexico City Vehicles.
       S.P.Beaton, G.A.Bishop, and D.H.Stedman.
       J. Air Waste Manage. Assoc. v.42 p.1424-1429 (1992)

  80.  Enhancements of Remote Sensing for Vehicle Emissions in Tunnels.
       G.A.Bishop, D.H.Stedman and 12 others from GM, EPA etc.
       Air & Waste v.44 p.168-175 (1994)
       
  81.  The Cost of Reducing Emissions from Late-Model High-Emitting
       Vehicles Detected Via Remote Sensing.
       R.M.Rueff.
       J. Air Waste Manage. Assoc. v.42 p.921-925 (1992)

  82.  On-road Vehicle Emissions: US studies.
       K.T.Knapp
       Sci.Total Environ. v.146/147 p.209-215 (1994)

  83.  IR Long-Path Photometry: A Remote Sensing Tool for Automobile 
       Emissions.
       G.A.Bishop, J.R.Starkey, A.Ihlenfeldt, W.J.Williams, and 
D.H.Stedman.
       Analytical Chemistry, v.61 p.671A-677A (1989)

  84.  A Cost-Effectiveness Study of Carbon Monoxide Emissions Reduction
       Utilising Remote Sensing.
       G.A.Bishop, D.H.Stedman, J.E.Peterson, T.J.Hosick, and 
P.L.Guenther
       Air & Waste, v.42 p.978-985 (1993)

  85.  A presentation to the California I/M Review Committee of results 
of
       a 1991 pilot programme.
       D.R.Lawson, J.A.Gunderson
       29 January 1992.   

  86.  On-Road Vehicle Emissions: Regulations, Costs, and Benefits.
       S.P.Beaton, G.A.Bishop, Y.Zhang, L.L.Ashbaugh, D.R.Lawson, and
       D.H.Stedman.
       Science, v.268 p.991-995. (1995)

  87.  Reference 25.
       Methods of Knock Rating. 15. Measurement of the Knocking 
       Characteristics of Automotive Fuels. v.4. p.3057-3065.
       J.M.Campbell, T.A.Boyd. 
       
  88.  Standard Test Method for Knock Characteristics of Motor and 
Aviation
       Fuels by the Motor Method.
       ASTM D 2700 - 92. IP236/83  
       Annual Book of ASTM Standards v.05.04 (1994).

  89.  Standard Test Method for Knock Characteristics of Motor Fuels by 
the 
       Research Method.
       ASTM D 2699 - 92. IP237/69  
       Annual Book of ASTM Standards v.05.04 (1994).

  90.  High Sensitivity of Certain Gasolines Remains a Problem.
       Hydrocarbon Processing, July 1994. p.11. 

  91.  Preparation of distillates for front end octane number ( RON 100C 
)
       of motor gasoline
       IP 325/82
       Standard Methods for Analysis and Testing of Petroleum and 
Related
       Products. Wiley. ISBN 0 471 94879 9 (1994).

  92.  Octane Enhancers.
       D.Simanaitis and D.Kott.
       Road & Track, April 1989. p.82,83,86-88.
 
  93.  Specification for Aviation Gasolines
       ASTM D 910 - 93
       Annual Book of ASTM Standards v.05.01 (1994).

  94.  Reference 1.
       - Chapter 19. R.A.Vere

  95.  Automotive Sensors Improve Driving Performance.
       L.M.Sheppard.
       Ceramic Bulletin, v.71 p.905-913 (1992).

  96.  Water Addition to Gasoline - Effect on Combustion, Emissions, 
       Performance, and Knock.
       J.A.Harrington.
       SAE Technical Paper 820314 (1982).

  97.  Reference 29.
       - Chapter 7.

  98.  Exhaust Valve Recession with Low-Lead Gasolines.  
       Automotive Engineering, November 1987. p.72-76.

  99.  Investigation of Fire and Explosion Accidents in the Chemical, 
Mining
       and Fuel-Related Industries - A Manual.
       Joseph M. Kuchta.
       US Dept. of the Interior. Bureau of Mines Bulletin 680 (1985).

 100.  Natural Gas as an Automobile Fuel, An Experimental study.
       R.D.Fleming and J.R.Allsup.
       US Dept. of the Interior. Bureau of Mines Report 7806 (1973).

 101.  Comparative Studies of Methane and Propane as Fuels for Spark 
Ignition
       and Compression Ignition Engines.
       G.A.Karim and I.Wierzba.
       SAE Paper 831196. (1983).

 102.  Some Considerations of the Safety of Methane, (CNG), as an 
Automotive
       Fuel - Comparison with Gasoline, Propane, and Hydrogen Operation.
       G.A.Karim.
       SAE Paper 830267. (1983).

 103.  Natural Gas (Methane), Synthetic Natural Gas and Liquified 
Petroleum
       Gases as fuels for Transportation.
       R.D.Fleming, R.L.Bechtold
       SAE Paper 820959. (1982).

 104.  The Outlook for Hydrogen.
       N.S.Mayersohn.
       Popular Science, October 1993. p.66-71,111.

 105.  Hydrogen as the Fuel for a Spark Ignition Otto Cycle Engine
       A.B.Allan.
       SAE Paper 821200. (1982).

 106.  Hydrogen as a Fuel for Vehicle Propulsion
       K.S.Varde, G.G.Lucas.
       Proc.Inst.Mech.Engrs. v.188 26/74 p.365-372 (1974).
  
 107.  Reference 7.
       - Volume 13. Hydrogen Energy.

 108.  Reference 7.
       - Volume 11. Fuel Cells.

 109.  The Clean Machine.
       R.H.Williams.
       Technology Review, April 1994. p.21-30.

 110.  Fuel Cells: Energy Conversion for the Next Century.
       S.Kartha, P.Grimes.
       Physics Today, November 1994. p.54-61. 

 111.  Hybrid car promises high performance and low emissions.
       M. Valenti.
       Mechanical Engineering, July 1994. p.46-49.

 112.  Water-Gasoline Fuels -- Their Effect on Spark-Ignition Engine
       Emissions and Performance.
       B.D.Peters, R.F.Stebar.
       SAE Technical Paper 760547 (1976)

 113.  ?
       Automotive Industries Magazine, December 1994.

 114.  Instrumental Methods of Analysis - 6th edition. 
       H.H.Willard, L.L.Merritt, J.A.Dean, F.A.Settle. 
       D.Van Nostrand. ISBN 0-442-24502-5 (1981).  

 115.  Research into Asymmetric Membrane Hollow Filter Device for Oxygen-
       Enriched Air Production.
       A.Z.Gollan. M.H.Kleper.
       Dept.of Energy Report DOE/ID/12429-1 (1985).
     
 116.  New Look at Oxygen Enrichment. I. The diesel engine.
       H.C.Watson, E.E.Milkins, G.R.Rigby.
       SAE Technical Paper 900344 (1990)

 117.  Thorpe's Dictionary of Applied Chemistry - 4th edition.
       Longmans. (1949).
       - Petroleum

 118.  Detonation Characteristics of Some Paraffin Hydrocarbons.
       W.G.Lovell, J.M.Campbell, and T.A.Boyd.
       Ind. Eng. Chem., v.23 p.26-29. (1931)

 119.  Secrets of Honda's horsepower heroics.
       C. Csere.
       Road & Track/Car & Driver?, May 1991. p.29.
  
     
11.2  Suggested Further Reading

   1.  Modern Petroleum Technology - any edition.
       Editor, G.D.Hobson.
       Wiley. ISBN 0 471 262498 (5th=1984).
         
   2.  Hydrocarbon Fuels.
       E.M.Goodger.
       MacMillan. (1975)
 
   3.  Alternative Fuels
       E.M.Goodger.
       MacMillan. ISBN 0-333-25813-4 (1980)
       
   4.  Kirk-Othmer Encyclopedia of Chemical Technology - 4th edition.
       Editor, M.Howe-Grant.
       Wiley. ISBN 0-471-52681-9 (1993) 
       - especially Alcohol Fuels, Gasoline and Other Motor Fuels, 
Hydrogen
         Energy and Fuel Cells chapters.

   5.  The Automotive Handbook. - any edition.
       Bosch.
  
   6.  SAE Handbook, volume 1. - issued annually.
       SAE. ISBN 1-56091-461-0 (1994).
       - especially J312, and J1297.

   7.  Proceedings of the xxth International Symposium on Alcohol Fuels.
       - Held every two years and most of the 10 conferences have lots 
of
         good technical information, especially the earlier ones.
       - various publishers.

   8.  Alternative Transportation Fuels - An Environmental and Energy
       solution.
       Editor, D.Sperling. 
       Quorum Books. ISBN 0-89930-407-9 (1989).

   9.  The Gasohol Handbook.
       V. Daniel Hunt.
       Industrial Press. ISBN 0-8311-1137-2 (1981).

  10.  The Science of Petroleum. 
       Various Authors.
       Oxford Uni. Press.(1938).
       - especially Part 4 "Detonation and Combustion".


                                                                                           
