A turbofan engine operates much like its predecessor, the turbojet. Air is compressed and ignited fuel is added to the air to send a stream of hot gas out of the rear of the engine, generating thrust. But a turbofan has at least one extra component: a fan. The fan usually mounts in front of the compressor and drives air around the engine, producing additional thrust. This also improves fuel efficiency.
The inlet collects air that flows through the engine's fan. Some of the air from the fan is routed through the engine where it is compressed in a multistage compressor. Ignited fuel is introduced to the air in the engine's combustor, sending the heated air rushing from the nozzle at the rear of the jet. In a turbofan, exhaust gas turns two turbines. One turbine turns the compressor through a connected shaft, and another is attached to a shaft that turns the fan.
Earlier turbojet engines could propel aircraft faster than most propeller-driven engines, but turbofan engines produce more thrust, since the engine's fan also produces thrust, in addition the hot exhaust gases. Turbofan engines are also quieter to operate than turbojets.
Turbofans are equipped on several military aircraft, and they are especially useful on passenger jets that strive for fuel economy and noise control. Turbofans in civilian applications generally use fans to push more air around the engine instead of though it. This further reduces noise and improves fuel efficiency. Military turbofans often emphasize thrust over noise reduction and fuel economy.
Air flowing through the engine operate a turbofan's compressor and fan, recycling energy. And extra thrust can be achieved by adding an afterburner to a turbofan engine. An afterburner adds fuel to the jet's hot exhaust. The combustion provides more thrust but uses lots of fuel.
