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AIRCRAFT PROPULSION : TURBOFAN ENGINE

Gas turbines are particularly suited for aircraft propulsion because they are light and compact and have a high power-to-weight ratio. Aircraft gas turbines operate on an open cycle called "Jet propulsion Cycle", as explained below . It can be of turbojet, turbofan or turboprop type.

TURBOFAN ENGINE :

The most widely used engine in aircraft propulsion is the turbofan engine where in a large fan driven by the turbine forces a considerable amount of air through a duct (cowl) surrounding the engine. The exhaust leaves the duct at a higher velocity, enhancing the total thrust of  the engine significantly. Some of the air entering the engine flows through the compressor, combustion chamber and turbine and the rest passes through the fan into a duct and is either mixed with the exhaust gases or is discharged separately. It improves the engine performance over a broad operating range. The ratio of the mass flow rates of the two streams is called the bypass ratio. 



                  By Pass Ratio = (m*total - m*turbine) / m* turbine

The bypass ratio can be varied in flight by various means. Turbofan engines deserve most of  the credit for the success of jumbo jets, which weigh almost 400,000kg and are capable of carrying 400 passengers for up to 10,000km at speeds over 950 km/h  with less than fuel per passenger mile. 

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