The GATE Grind

GATE 2019 AE – Question 20

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

A ramjet has lower propulsive efficiency than a low-bypass turbofan producing the same thrust under the same flight conditions because it has

  1. Greater loss of exhaust kinetic energy.
  2. Lower thrust power.
  3. No self-starting capability.
  4. Higher thrust-to-weight ratio.

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Show answer and explanation

Correct answer: (A) Greater loss of exhaust kinetic energy.

Explanation

At equal thrust F and flight speed V, useful thrust power FV is equal. A higher exhaust velocity for a smaller mass flow leaves more kinetic energy in the exhaust for the same thrust. This excess exhaust kinetic-energy loss lowers propulsive efficiency. Thus A; self-starting and weight are different characteristics.

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