TURBOFAN ENGINE
TURBOFAN ENGINE
The turbofan engine is a combination of the turbo prop and the turbojet engines combining the advantages of both. The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the turbo portion refers to a gas turbine engine which achieves mechanical energy from combustion, and the fan, a ducted fan that uses the mechanical energy from the gas turbine to accelerate air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. In the 1950s, Rolls-Royce introduced the first turbofan in the world, namely, RB.80 Conway.
Classification
1. According to Fan Location
(a) Forward Fan Turbofan Engine
(b) AFT Fan Turbofan Engine
2. According to Spools
(a) Single Spool Turbofan Engine
(b) Double Spool Turbofan Engine
(c) Triple Spool Turbofan Engine
3. According to by-pass ratio
(a) Low by-pass ratio Turbofan Engine
(b) High by-pass ration Turbofan Engine
Construction
The Turbofan engine consists of-
1. Fan
2. Compressor
3. Combustion Chamber
4. Turbine (Low & High Pressure)
5. Fan Nozzle
Working
Air from the atmosphere enters employing a low pressure ducted fan. The air after passing through the fan is divided into two streams, namely primary air and secondary air. The primary air flow through the turbofan engine consisting of compressor, combustion chamber, turbine and exhaust nozzle. Combustion takes place in the combustion chamber and the thrust is produced in the opposite direction. The secondary air (or) by pass air (or) cold air at relatively lower pressure flows around the turbofan engine and expands in the fan nozzle. Hence thrust is produced.
The thrust developed by the secondary air is at lower velocity and the thrust developed by the primary air is at much higher velocity The total thrust produced in this engine is the sum of thrust produced by the primary air and the secondary air. This total thrust propels the air craft.
The ratio of the mass flow rates of cold air and the hot air is known as By Pass Ratio.
Advantages
1. Thrust developed is higher than turbojet engine.
2. Weight per unit thrust is lower than turbo prop engine.
3. Less noise.
4. High take-off thrust.
Disadvantages
1. Increased frontal area.
2. Fuel consumption is high compared to turbo prop engine.
3. Construction is complicated compared to turbojet engine.
4. Lower speed limit than turbojet engine.
Thank you Pushkar.
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