Diesel Engine

A form of compression-ignition reciprocating heat engine. In a diesel engine, the fuel-air mixture inside the cylinder is ignited by the heat of compression rather than by an electric spark. The air inside the cylinder is heated as it is compressed and, when the piston is near the top of its stroke, the air is very hot. A fuel injector sprays a very fine mist of fuel into the hot air and the fuel ignites and burns. Heat added by the burning fuel expands the air and pushes the piston down.