Turbofan Engine


CFM56-3 turbofan, lower half, side view.

A Rolls-Royce RB211 turbofan mounted on a Boeing 747.

A turbofan is a type of aircraft engine consisting of a ducted fan which is powered by a gas turbine. Part of the airstream from the ducted fan passes through the gas turbine core, providing oxygen to burn fuel to create power. However, most of the air flow bypasses the engine core, and is accelerated by the fan blades in much the same manner as a propeller. The combination of thrust produced from the fan and the exhaust from the core is a more efficient process than other jet engine designs, resulting in a comparatively low specific fuel consumption.

A few designs work slightly differently and have the fan blades as a radial extension of an aft-mounted low-pressure turbine unit.

Turbofans have a net exhaust speed that is much lower than a turbojet. This makes them much more efficient at subsonic speeds than turbojets, and somewhat more efficient at supersonic speeds up to roughly Mach 1.6, but have also been found to be efficient when used with continuous afterburner at Mach 3 and above.

All of the jet engines used in currently manufactured commercial jet aircraft are turbofans. They are used commercially mainly because they are highly efficient and relatively quiet in operation. Turbofans are also used in many military jet aircraft.

Schematic diagram showing the operation of a turboprop engine