The Chemistry of Gasoline Engines


Gasoline car engines have been around for quite a while, our whole lives in fact. We often take them for granted too, but they have helped make the world the way it is today. In my life, they are my main form of transportation and make my life a lot easier. I was very interested in learning about the chemistry of gasoline car engines for several reasons. For one thing, I have always liked cars. Also, I am very mechanically inclined, so engines are fascinating to me. But the greatest reason by far that I wanted to learn more about engines was the fact that I am currently taking one apart for another project and figured it would be great to better learn why engines are made the way they are and the chemistry behind them.

Composition of ...

Gasoline engines are composed of many substances. One of these is cast iron. Found more in older engines, cast iron is very strong and can withstand great temperatures. Gasoline is also found in engines. Commonly with a formula of C8H18, it can be very varied. Aluminum alloys are becoming very common in newer engines. They are lighter, easier to make, cheaper, and more resistant to corrosion than cast iron. They are not as strong as cast iron however, so cast iron is still generally used to line cylinders.

Main Chemicals, Compounds, Components

To make a gasoline engine do it’s job, fuel is needed. Therefore, gasoline is a main compound in an engine. Today’s gasoline has a formula of C8H18. Gasoline is a clear/yellowish liquid when refined and produced, however, gasoline vaporizes at low temperatures. This is part of what makes gasoline great for fuel.

Another main compound found in engines, particularly old ones, is cast iron. Cast iron is very dense, very strong, and very heavy. Cast iron can withstand a lot, including the great temperatures found inside engines. Cast iron is also used in so many other things. One example is Dutch Ovens. These are used for cooking, and therefore need to also withstand great temperatures. Cast iron can also be found in older plumbing systems and bathtubs.

Chemistry's Role

Gasoline is very combustible under the right circumstances. When in an engine, it is combined with air and vaporized. The vapor/air mixture is the combustible combination. As a petroleum based solution, gasoline is very combustible. It contains several hydrocarbons as well. Surprisingly, Gasoline consists of mostly organic compounds that are combined and refined at a refinery when it is made.

Cast iron is created by being cast in a mold at a plant, hence the ‘cast’ before the iron. Cast iron has a higher carbon level than steel and is very brittle. Though brittle, cast iron is incredibly hard and it takes extreme force to crack it or flat out break it. Cast iron is not something that can be bent, dented or shaped after it is cast. All these factors make it a great material to use in an engine, where flexing and soft metal cannot be tolerated. An engine block will crack or melt down in extreme cases, not bend or flex. In modern aluminum engines, the block must have cylinder sleeves made of cast iron if it is to last any period of time because aluminum simply cannot handle the beating and temperatures the cylinders take.

Background Research

To understand the chemistry of the gasoline engine that is probably in your car, you must first know the basics of how an engine works. There are many types of gasoline engines. Common gasoline engines may vary between a V-shaped engine, inline engine, opposed-piston engine (aka flat or boxer engine), and sometimes rotary engines. Each of these engines, with the exception of rotary engines, implement the use of pistons in cylinders. In these engines, gasoline is either mixed with air in a carburetor and pushed into the cylinder, or mixed with air in the cylinder via fuel injection. Once the gasoline/air mixture is ignited via the spark plugs, the pistons are forced downward, which transfers the energy of the explosion from the piston to the crankshaft. The crankshaft eventually transfers energy to the transmission, then possibly to a transfer case, which connects to the driveshaft(s) and so on. The fuel that gasoline engines are engineered for is obviously gasoline, but other fuels like propane and pure ethanol can be used too. Gasoline as a fuel varies in many ways. One of the largest engineered variations that has been demonstrated America in the last century is the transition from leaded to unleaded fuel. Today, all the gas you get at the pump is unleaded, but not too long ago, you could still buy leaded fuel. Older engines ran better with it too. The lead in the gasoline actually provided some lubrication, and so when engines designed for unleaded fuel no longer had access to it, they would wear out faster because there was more abrasion occurring between the parts. Engine blocks themselves are usually made out of cast iron or aluminum alloys today. Each material has it’s advantages and disadvantages.


Source One:

    • An internal combustion engine has a combustion of a fuel that occurs with an oxidizer (usually air) in a combustion chamber (usually a cylinder).
    • Transforms chemical energy into mechanical energy
    • Can classify engines by:
      • The number of strokes
      • The type of ignition
      • The mechanical/thermodynamical cycle
    • Block made out of cast iron or aluminum

Source Two:

    • Gasoline engines designed to run on gasoline, or “petrol” if you’re British
    • Gasoline engines in vehicles are internal combustion engines with some form of spark ignition
      • Spark Plugs are used as a spark source
    • Gasoline is either mixed with air via a carburetor, or via fuel injection.
    • Gasoline engines run at a higher speed than diesel engines.
    • When fuel and air is compressed too much, auto ignition can happen
      • Damages engine
      • Is what happens in a diesel engine
    • Engines cooled with air or with liquid via a radiator or cooling jackets

Source Three:

    • Cylinder blocks are usually made out of cast iron or aluminum alloys
      • Aluminum blocks are lighter
      • Aluminum blocks transfer heat to coolant better
      • Iron blocks are stronger, but heavier
      • Cylinder liners make aluminum blocks not a problem, and therefore maybe even better.

Source Four:

    • Gasoline is a petroleum based substance
    • Consists of mostly organic compounds
    • Measured by octane ratings
    • Gasoline may contain ethanol and many other chemicals for various reasons
    • Should be “stable” for at least six months if stored right
      • Old gasoline goes bad
      • Old gasoline hard on engines
    • Is a hydrocarbon
    • Obviously flammable
    • May contain at least 15 hazardous chemicals

Source Five:

    • Gasoline is a mixture containing over 500 hydrocarbons
    • May have 5-12 carbons
    • Often produced by fractional distillation of crude oils
    • Different grades are better for different engines
      • Depends on compression ratios

Source Six:

    • Rotary engine conceived by Felix Wankel in Germany
    • Rotating equilateral triangle instead of cylinders
    • Uses water in cooling jackets to cool engine
    • ⅓ as many parts as in a normal engine
    • Advantages are:
      • Lighter
      • Less expensive initially
      • Supposedly less maintenance
      • Smooth performance

Source Seven:

    • Ethanol fuel is ethyl alcohol
      • Found in alcoholic beverages

About the Author

Hayden Trapp is a Junior at Billings Senior High. He enjoys biking, skiing, camping, and other outdoor activities. Hayden also really enjoys mechanical projects. He is currently fixing up his truck for the purpose of a school project, as a learning experience, and eventually for personal use. This project has given Hayden an opportunity to learn more about the engine he is working on. Hayden is currently in the Platinum Program, and therefore an honors student. He has also lettered in band. Hayden is a part of STEM club and Senior’s tech club as well.