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Home > Technical Articles > More Than You Ever Wanted to Know About Gasoline

DriveWerks Technical Bulletin:

More Than You Ever Wanted to
Know About Gasoline

from usenet


FAQ: Automotive Gasoline Bruce Hamilton 

This FAQ is posted monthly to the Usenet groups news.answers, rec.answers, and The latest copy should be available by FTP from in the pub/usenet-by-hierarchy/rec/autos/tech directory, and also available on the WWW from sites that automatically convert those FAQs. Changes: - added a little more data on US crude oil resources.

1. Introduction, Intent, Acknowledgements, and Abbreviations

1.1  Introduction and Intent.

The intent of this FAQ is to provide some basic information on gasoline 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 and 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 )

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

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 gasoline.

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