Aircraft engine is a type of propulsion system used to power aircraft. The three most common types of aircraft engines are ramjet, JET, and turbojet. A ramjet is an engine that uses the forward motion of the aircraft to compress incoming air for combustion without the use of a compressor. A JET is an engine that uses a turbine to compress incoming air for combustion. Finally, a turbojet is an engine that uses a turbine to compress incoming air for combustion and also has an additional turbine to extract energy from the exhaust gases.