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GATE 2024 AE – Question 41

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

An aircraft with a turbojet engine is flying at 250 m/s. The uninstalled thrust produced by the engine is 60000 N. The heating value of the fuel is $44 \times 10^6$ J/kg. The engine has a thermal efficiency of 35% while burning the fuel at a rate of 3 kg/s. Assume the engine exit pressure to be equal to the ambient pressure. What is the propulsion efficiency of the engine under these conditions (in percentage)?

  1. 32.5
  2. 35.0
  3. 11.4
  4. 92.4

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Correct answer: (A) 32.5

Explanation

The rate of heat release is $3 \times 44 \times 10^6 = 132$ MW, and 35% of this becomes kinetic energy of the jet: $46.2$ MW. The thrust power is $FV_0 = 60000 \times 250 = 15$ MW. The propulsive efficiency is $\frac{15}{46.2} = 0.325$, or 32.5%.