The internal combustion engine is one of the most useful inventions of modern time. It uses linear motion to create rational motion, which is what moves a vehicle forward. However, the forward motion would not occur without the process that the internal combustion engine uses to converts heat energy into power, and power into movement. But how exactly does this happen? Long story short, when a high energy fuel, namely gasoline, is introduced into a small space and ignited, it will explode, thus creating high energy gas that will expand and explode. It is from the energy of this explosion that motion takes place.

Without the benefit of a diagram, explaining the process that occurs is rather difficult, but perhaps this description will be useful nonetheless.Internal combustion engines (like that found in most cars) generate motion by what is referred to as a four stroke process. This process is rotational and continuous. Simply put, these are:

1. Intake
2. Compression
3. Combustion
4. Exhaust

INTAKE

In the engine's camshaft, a cam rotates, setting off a series of events. During the intake stroke, the intake valve, rocker arm, and spring are pushed by the motion of the cam, so that a small amount of fuel is able to enter the engine block. The fuel and air in the engine block are, at this point, uncompressed by the piston, and are therefore not generating energy.

COMPRESSION

As the cam continues to rotate, the piston, which rotates around the crankshaft, will eventually move up into the space in the engine block. The piston is cylindrical in shape, as is the engine block, so as it fills the space, the air inside the engine block, along with the amount of fuel that entered during the INTAKE stroke, is being compressed.

COMBUSTION

As soon as the piston is at the highest point of it's stroke, and the air/fuel mixture is as compressed as possible, the spark plug ignites a spark and the mixture undergoes a controlled explosion. The amount of force exerted by the explosion immediately pushes the piston down to the lowest part of its stroke.

EXHUAST

The final stroke is that in which the products of the chemical reaction from the explosion are given off as exhaust. Almost any chemical reaction of this type produced heat as a by-product as well as some gaseous emissions. The heat is used to create motion in the engine, but the gaseous emissions must be removed from the system. The exhaust is given off in the vehicle's tailpipe.

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