The GATE Grind

GATE 2026 AE – Question 24

Propulsion · Engine performance: ramjet, turbojet, turbofan, turboprop, turboshaft and after-burners · 1 mark · Multiple select

For a given air-standard power, the propulsive efficiency of a turbofan engine is more than that of a turbojet engine. Which of the following is/are the reason(s) for this?

  1. The mass flow rate is more for a turbofan engine
  2. The exit velocity is lower for a turbofan engine
  3. A turbofan engine operates at a lower altitude
  4. The fan of a turbofan engine consumes lesser power

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Show answer and explanation

Correct answer: (A) The mass flow rate is more for a turbofan engine; (B) The exit velocity is lower for a turbofan engine

Explanation

For the same thrust or power, a turbofan accelerates a larger mass flow to a smaller velocity increase. The propulsive efficiency $\frac{2}{1 + V_e/V_0}$ is higher when the exit velocity is closer to the flight speed.