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GATE 2019 AE – Question 39

Propulsion · Aerothermodynamics of aircraft engines: thrust, efficiency, range and the Brayton cycle · 2 marks · Multiple choice

If compressor efficiency decreases in a gas-turbine engine while turbine-inlet temperature remains fixed, the thrust-specific fuel consumption

  1. Decreases because less heat is supplied.
  2. Remains unchanged.
  3. Increases because greater compressor work is required.
  4. Decreases because thrust increases.

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Correct answer: (C) Increases because greater compressor work is required.

Explanation

For a given pressure ratio, compressor work is $c_p(T_{02s}-T_{01})/\eta_c$. Lower efficiency raises required work. More turbine work must be extracted to drive it, leaving less useful jet output under the intended fixed operating comparison. Fuel per unit thrust consequently increases, C.

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