A turbofan engine is a jet engine in which the excess shaft power produced by the turbine is used to drive a fan, which in turn provides additional air that gives extra thrust to the aircraft. Thus, part of the air flowing into the engine intake, after being processed in the fan section, bypasses the core engine as it expands in a separate bypass duct to provide “cold” thrust. The turbofan accelerates a larger mass of air to a lower velocity than a turbojet engine for a higher propulsive efficiency.
Some types of turbofan engine mix the cold flow with the hot exhaust gas from the core engine to increase propulsive efficiency as is the case with the V.2500 engine. The amount of air that is bypassed in relation to the air that flows through the core engine is termed the bypass ratio. Therefore, a distinction is made between low and high bypass-ratio engine. Low bypass-ratio turbofan engine is employed in supersonic combat aircraft, while the high bypass-ratio machine is used both in transport and commercial aircraft, such as the Pratt & Whitney PW4000 and the GE90-115B.
Parts and Components
A turbofan engine consists of a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber (burner), a high-pressure turbine, a low-pressure turbine, and an exhaust nozzle. The high-pressure compressor share the same shaft with the high-pressure turbine, while the low-pressure compressor and low-pressure turbine turn on another shaft, which is usually inside the HP compressor’s shaft.
Below, a schematic picture of a low bypass-ratio turbofan engine
