Two forms of jet engine. In the turbojet, air passing into the air intake is compressed by the compressor and fed into the combustion chamber where fuel burns. The hot gases formed are expelled at high speed from the rear of the engine, driving the engine forwards and turning a turbine which drives the compressor. In the turbofan, some air flows around the combustion chamber and mixes with the exhaust gases. This arrangement is more efficient and quieter than the turbojet.