How Does a Combustion Engine Work?

There are actually two kinds of combustion engines―internal combustion engines and external combustion engines. You can find an internal combustion engine in most motor vehicles, including boats and motorcycles. You can even find them in some trains and airplanes.

Internal combustion engines are more widely used, whereas external combustion engines are used mainly for steam engines, such as those used for older steam boats and trains.

There are four basic types of internal combustion engines: Otto-cycle, diesel, rotary, and gas turbine. The Otto-cycle engine, or four-stroke, is the engine you're most likely to see in regular motor-vehicles today.

Internal Combustion Engines

With an internal combustion engine, fuel is burned inside the engine in what is known as a combustion chamber. The combustion chamber is an enclosed space where the gasoline goes. Once the gas of the confined gasoline expands, it produces energy.

The more compressed the mixture of air and fuel, the greater the risk of it bursting into flames. This is why high octane gasoline is recommended for high performance cars. Although it may cost a bit more, it prevents the higher compression of these engines from premature combustion.

The Four-Stroke Combustion Cycle

Although you can find two-stroke combustion cycles in some boat and motorcycle engines, as well as snowmobile and personal watercraft engines, most internal combustion engines found in today's cars use the four-stroke combustion cycle. This cycle turns fuel into motion, i.e., it makes your car go.

Very simply put, the first stroke intakes fuel; the second compresses the fuel; the third combusts the fuel; and the fourth exhausts the fuel.

The four-stroke combustion cycle's advantages over the two-stroke combustion cycle are the fuel efficiency and cleanliness―two very attractive qualities in today's world of ever-increasing gas prices and air pollution.

The Four-Stroke Engine

Knowing the parts of a four-stroke engine will help you understand how an internal combustion engine works.

Your basic four-stroke engine is going to include the following parts:

• Crankshaft, which sets the linear piston into rotation.

• Camshaft(s), which open the valves once every two times the crankshaft rotates.

• Valves, or poppet valves, which control the flow of fuel.

• Cylinder(s), which is where the piston travels.

• Spark plug(s), which ignite the compressed fuel. There is one spark plug for every cylinder.

• Piston, which exerts force on the fuel inside the cylinder(s).

• Crank, which is the bent part of the shaft that changes motion from reciprocating (back and forth or up and down) to circular, or vice versa. This motion leads to pushing the piston down, pushing the crankshaft round, and setting the wheels of the vehicle in motion.

Summary

If the majority, or all, of your experience with vehicles has been behind the wheel and not under the hood, much of this probably sounds foreign to you. Let's recap.

Take another look at the description of the four-stroke combustion cycle.

During the first stroke of the cycle―the intake stroke―the intake of fuel occurs. This means that your vehicle's fuel, most often gasoline, fills up the combustion chamber.

Once the fuel is in the combustion chamber,―the compression stroke―compresses the fuel. This is to prepare it for ignition since fuel will ignite easier when pressurized.

Now that the fuel is compressed, the spark plugs will ignite the fuel, similar to a tiny explosion, during ―the combustion stroke.

During the exhaust stroke, the fumes of the burned fuel are pushed out into the exhaust system.