MadSci Network: Engineering

Re: Howdoes gas make a car go?

Date: Mon Jan 29 14:37:32 2001
Posted By: David Ellis, Researcher, NASA Lewis Research Center
Area of science: Engineering
ID: 980114510.Eg

A gasoline car engine is an internal combustion engine. It uses a four-stroke combustion cycle. Gasoline or gas is the fuel. Oxygen from the air is the oxidizer. There are also diesel engines which operate a bit differently and use diesel fuel.

Gasoline is a hydrocarbon. That means it is a very long molecule made up primarily of hydrogen and carbon. Hydrogen and carbon have a stronger chemical affinity for oxygen than each other. So given a chance the hydrogen and carbon atoms will combine with oxygen to form water and carbon monoxide/dioxide.

They cannot do it spontaneously, though. They need an ignition source. In the case of a car engine, that is a spark from the spark plug. Once they get the little bit of energy needed to start the chemical reaction, they oxidize (chemically react with oxygen) or burn very rapidly. That gives off a large amount of energy. Most of that energy is in the form of heat. The heat energy causes the combustion gases to expand rapidly.

In a car engine, gases are trapped in a cylinder. The energy from burning the gasoline is turned into useful work by using the rapidly expanding gases (water, carbon monoxide, carbon dioxide) to push a piston. The piston is connected to a crankshaft. The pistons moving in and out turn the crankshaft. As the crankshaft turns it turns the wheels as well. A transmission is used to make turning the wheels easier at low speeds and more efficient at high speeds.

There are many good sources on internal combustion engines. Some are given below.


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