Internal combustion engine
Internal combustion engine, heat engine in which fuel is burned inside the engine itself. It contrasts with an external combustion engine (such as the steam engine), in which fuel is burned in a separate furnace. By far the most common type of internal-combustion engine is the gasoline engine, which propels practically all automobiles. Another common type is the diesel engine used in trucks and many locomotives and ships. Both types work in a similar way, burning fuel inside closed cylinders to produce reciprocating (to and fro) motion of pistons. As machines, these engines are very inefficient. The gasoline engine can convert only about 20% of the heat energy released by burning fuel into useful work. The diesel engine is a little more efficient, being able to utilize some 30% of the energy released. Gas turbines and jet and rocket engines can also be classified as internal combustion engines, although they are of a rather different kind. They burn fuel continuously in a combustion chamber, generating hot gases that spin turbines or producing propulsive thrust by reaction.
See also: Engine.