Gasoline FAQ - Part 1 of 4

Archive-name: autos/gasoline-faq/part1 Posting-Frequency: monthly Last-modified: 17 November 1996 Version: 1.12

FAQ: Automotive Gasoline Bruce Hamilton snipped-for-privacy@irl.cri.nz

This FAQ is posted monthly to the Usenet groups news.answers, rec.answers, and rec.autos.tech. The latest copy should be available on the WWW from sites that automatically convert those FAQs, such as

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Changes:

- added a little more data on US crude oil resources.

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Subject: 1. Introduction, Intent, Acknowledgements, and Abbreviations

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 Acknowledgements.

Thanks go to all the posters in sci.energy and rec.autos.tech who spend valuable time responding to questions. I would also like to acknowledge the considerable effort of L.M.Gibbs of Chevron, who has twice spent his valuable time courteously detailing errors and providing references for his corrections. All remaining errors and omissions are mine.

1.3 Abbreviations.

AKI = Antiknock 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 )

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Subject: 2. Table of Contents

  1. Introduction, Intent, Acknowledgements, and Abbreviations 1.1 Introduction and Intent. 1.2 Acknowledgements. 1.3 Abbreviations. 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 or 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 Octane Number Requirement of a Vehicle? 7.2 What is the effect of Compression ratio? 7.3 What is the effect of changing the air-fuel ratio? 7.4 What is the effect of changing the ignition timing 7.5 What is the effect of engine management systems? 7.6 What is the effect of temperature and Load? 7.7 What is the effect of engine speed? 7.8 What is the effect of engine deposits? 7.9 What is the Road Octane Number of a Fuel? 7.10 What is the effect of air temperature?. 7.11 What is the effect of altitude?. 7.12 What is the effect of humidity?. 7.13 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

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Subject: 3. What Advantage will I gain from reading this FAQ?

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.

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Subject: 4. What is Gasoline?

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 since then.

4.2 When will we run out of crude oil?

It has been estimated that the planet contains over 6.4 x 10^15 tonnes of organic carbon that is cycled through two major cycles, but only about 18% of that contributes to petroleum production. The primary cycle ( turnover of

2.7-3.0 x 10^12 tonnes of organic carbon ) has a half-life of days to decades, whereas the large secondary cycle ( turnover 6.4 x 10^15 tonnes of organic carbon ) has a half-life of several million years [4]. Much of this organic carbon is too dilute or inaccessible for current technology to recover, however the estimates represent centuries to millenia of fossil fuels, even with continued consumption at current or increased rates [5].

The concern about "running out of oil" arises from misunderstanding the significance of a petroleum industry measure called the Reserves/Production ratio (R/P). This monitors the production and exploration interactions. The R/P is based on the concept of "proved" reserves of fossil fuels. Proved reserves are those quantities of fossil fuels that 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 proved reserves quantity divided by the production in the last year, and the result will be the length of time that those remaining proved reserves would last if production were to continue at the current level [6]. It is important to note the economic and technology component of the definitions, as the price of oil increases ( or new technology becomes available ), marginal fields become "proved reserves". We are unlikely to "run out" of oil, as more fields become economic. Note that investment in exploration is also linked to the R/P ratio, and the world crude oil R/P ratio typically moves between

20-40 years, however specific national incentives to discover oil can extend that range upward.

Concerned people often refer to the " Hubbert curves" that predict fossil fuel discovery rates would peak and decline rapidly. M. King Hubbert calculated in 1982 that the ultimate resource base of the lower 48 states of the USA was 163+-2 billion barrels of oil, and the ultimate production of natural gas to be 24.6+-0.8 trillion cubic metres, with some additional qualifiers. As production and proved resources were 147 billion barrels of oil and 22.5 trillion cubic metres of gas, Hubbert was implying that volumes yet to be developed could only be 16-49 billion barrels of oil and 2.1-4.5 trillion cubic metres. Technology has confounded those predictions for natural gas [6a].

The US Geological Survey has also just increased their assessment of US ( not just the lower 48 states ), inferred reserves crude oil by 60 billion barrels, and doubled the size of gas reserves to 9.1 trillion cubic metres. When combined with the estimate of undiscovered oil and gas, the totals reach 110 billion barrels of oil and 30 trillion cubic metres of gas [7]. When the 1995 USGS estimates of undiscovered and inferred crude oil are calculated for just the lower 48 states, they totalled ( in 1995 ) 68.9 billion barrels of oil, well above Hubbert's highest estimate made in 1982. The current price for Brent Crude is approx. $22/bbl. The world R/P ratio has increased from 27 years (1979) to 43.1 years (1993). The 1995 BP Statistical Review of World Energy provides the following data [6,7].

Crude Oil Proved Reserves R/P Ratio Middle East 89.4 billion tonnes 93.4 year USA 3.8 9.8 years USA - 1995 USGS data 10.9 33.0 years Total World 137.3 43.0 years

Coal Proved Reserves R/P Ratio USA 240.56 billion tonnes 247 years Total World 1,043.864 235 years

Natural Gas Proved Reserves R/P Ratio USA 4.6 trillion cubic metres 8.6 years USA - 1995 USGS data 9.1 17.0 years Total World 141.0 66.4 years.

One billion = 1 x 10^9. One trillion = 1 x 10^12. One barrel of Arabian Light crude oil = 0.158987 m3 and 0.136 tonnes.

If the crude oil 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 [8].

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 [9]. This then lead to the long search for antiknock agents, culminating in tetra ethyl lead [10]. Typical mid-1920s gasolines were 40 - 60 Octane [11].

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. Octane ratings, lead levels, and vapour pressure increased, whereas sulfur content and olefins decreased. 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, lead levels plummetted, octanes initially decreased, and then remained 2-5 numbers lower, vapour pressures continued to increase, and sulfur and olefins remained constant, while aromatics increased. In 1990, the US Clean Air Act started forcing major compositional changes on gasoline, resulting in plummeting vapour pressure and increaing oxygenate levels. These changes will continue into the 21st Century, because gasoline use in SI engines is a major pollution source. Comprehensive descriptions of the changes to gasolines this century have been provided by L.M.Gibbs [12,13].

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 [14].

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

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