A jet engine is a type of air-breathing gas turbine engine that generates thrust by accelerating a mass of air out of its rear. Operating on principles related to the Brayton cycle, the general process involves drawing in ambient air, compressing it substantially, mixing it with fuel and combusting the resulting mixture to create high-temperature, high-pressure gases. These hot gases then expand through a turbine, which drives a compressor, before exiting the engine through a nozzle. The rapid expulsion of this exhaust gas, combined with the intake of air, creates a substantial net forward force, or thrust. Modern variations of these engines include turbofans, which utilize a large fan at the front to accelerate the majority of the incoming air and generate lift, thereby improving overall fuel efficiency compared to earlier, pure turbojet designs.