
The diesel engine gets the greatest thermal efficiency of any standard internal or external burning engine due to its very high compression ratio.

This contrasts with spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which use a spark plug to ignite an air-fuel mixture.

The diesel engine (also known as a compression-ignition engine) is an inner combustion engine that uses the heat of compression to initiate ignition and burn the fuel that happens to be injected into the combustion chamber.
