GATE 2023 AE – Question 28
From the options given, select all that are true for turbofan engines with afterburners.
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Show answer and explanation
Correct answer: (A) Turning afterburner ON increases specific fuel consumption.; (B) Turbofan engines with afterburners have variable area nozzles.
Explanation
Check each statement about a turbofan with an afterburner (reheat).
- **A. Afterburner ON increases specific fuel consumption.** True. Burning extra fuel in the afterburner gives a large thrust increase at the cost of a much larger fuel flow per unit thrust, so TSFC rises. ✓
- **B. Engines with afterburners have variable-area nozzles.** True. The nozzle throat has to open when the afterburner is lit, to pass the hotter, lower-density gas without raising the pressure upstream and upsetting the compressor and turbine. ✓
- **C. Afterburner ON decreases specific fuel consumption.** False (opposite of A).
- **D. Afterburner ON increases stagnation pressure.** False. Heat addition at flow speed causes a **loss** of stagnation pressure (Rayleigh flow), and there is no work input in the afterburner.
Answer **A and B**.