An engine is a machine which converts the energy chemistry, electric, etc, in energy mechanic, which is able to produce a movement. There are two types of engine: combustion, internal and external combustion. Nowadays the internal combustion engine is used more in cars, tractors, etc, and is more efficient than external combustion engine.

The internal combustion engine has four stages to produce the movement.

First stage: Admission

In this phase gas goes to the combustion chamber, the valves are responsible for letting gas go into the chamber.

Second stage: Compression

The gas is compressed by a piston in the combustion chamber while the valves are closing.

Third stage: Power

When the gas is totally compressed the spark plug generates a spark and the gas explodes.

Fourth stage: Exhaust

After the explosion the piston goes toward its lowest position. Finally the valves let the gas out and the cycle is finished.

Flavio, Upper-Intermediate