An airbreathing jet engine (or ducted jet engine) is a jet engine in which the exhaust gas which supplies jet propulsion is atmospheric air,[1] which is taken in, compressed, heated, and expanded back to atmospheric pressure through a propelling nozzle.[2] Compression may be provided by a gas turbine, as in the original turbojet and newer turbofan,[3][4] or arise solely from the ram pressure of the vehicle's velocity, as with the ramjet and pulsejet.[5]
All practical airbreathing jet engines heat the air by burning fuel.[1] Alternatively a heat exchanger may be used, as in a nuclear-powered jet engine.[6] Most modern jet engines are turbofans, which are more fuel efficient than turbojets because the thrust supplied by the gas turbine is augmented by bypass air passing through a ducted fan.[4]
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