Aerospace Propulsion - I Mid - I, September - 2014

1.Thermodynamic cycle on which the jet engine operates can be
  • Open Rankine cycle only
  • Either open or closed Rankine cycle
  • Open Brayton cycle only
  • either open or closed Brayton cycle
Answer: C
2.Which one of the following engines should be used by a subsonic passenger transport airplane for minimum specific fuel consumption?
  • Turbojet engine with afterburner
  • Turbofan engine
  • Ramjet engine
  • Scramjet engine
Answer: B
3.A turbojet engine is operating with afterburner off. If the afterburner is switched on, then
  • Both thrust and SFC decrease
  • Thrust increases and SFC decreases
  • Thrust decreases and SFC increases
  • both thrust and SFC increase
Answer: D
4.A main objective of bypass in a turbo fan engine is to increase
  • Mass flow rate through engine inlet
  • Turbine inlet temperature
  • Mass flow rate through exhaust nozzle
  • Compressor pressure ratio
Answer: C
5.Which of the following is not true for a Ramjet engine?
  • A Ramjet engine has high thrust to weight ratios
  • It works well at off design Mach number without a variable geometry diffuser and supersonic spike
  • A Ramjet engine by nature of its air compressor does not provide static thrust
  • Fuel consumption by a Ramjet engine at subsonic speeds is very high compared to other air breathing Engines
Answer: B
6.For a given fuel flow rate and thermal efficiency, the take-off thrust of a gas turbine engine burning aviation turbine fuel (considering fuel –air ratio << 1) is
  • Directly proportional to exhaust velocity
  • Inversely proportional to exhaust velocity
  • Independent of exhaust velocity
  • directly proportional to square of the exhaust velocity
Answer: B
7.The function of diffuser is to
  • Increase the pressure
  • Decrease the velocity
  • Decrease the pressure
  • Increase the velocity
Answer: B
8.The pressure ratio in any one stage of a jet engine compressor is limited by
  • Entry stagnation temperature in that stage
  • Entry Mach number in that stage
  • Pressure gradient induced separation in that stage
  • Mass flow rate in that stage
Answer: C
9.An aircraft propeller flies at speed of 440 km/h. The diameter of the propeller is 4.1 m and the speed ratio is 0.8. The ambient conditions of air at the flight altitude are T = 255 K and p = 0.55 bar. The thrust obtained by the propeller engine is
  • 42.67 kN
  • 41.67 kN
  • 43.67 kN
  • 40.67 kN
Answer: B
10.An aircraft cruising at a Mach number of 0.8 at an altitude where the ambient static pressure is 95 kPa. The diffuser exit total pressure is 140 kPa. Assuming there is no change in specific heat at constant pressure across the diffuser and ratio of specific heats is 1.4, the adiabatic efficiency of the intake is
  • 0.988
  • 0.915
  • 0.722
  • 0.684
Answer: B
11.The ratio of flight speed to the exhaust velocity for maximum propulsion efficiency is _______.
Answer: 1
12.The ideal static pressure coefficient of a diffuser with an area ratio of 2.0 is _______________.
Answer: 0.75
13.In a turbojet engine, thrust specific fuel consumption ___________________ with increasing compressor pressure ratio and ____________________________with increasing turbine inlet temperature (with in range of operation).
Answer: Decreases, Increases
14.Maximum pressure losses occur in an engine across _________________.
Answer: Compressor
15.In a gas turbine engine thermodynamic cycle, heat injection takes place at 11.2 atm and heat rejection takes place at atmospheric pressure, then the efficiency of the cycle is _________, given that the heat capacity ratio of the working substance is 1.3.
Answer: 42.7%
16.An air breathing aircraft flying at an altitude where the air density is half the value at ground level. With reference to ground level , the air fuel ratio at this altitude will be ____________
Answer: 1.414
17.For ideal ramjet engine, the exit Mach number is ____________ incoming Mach number.
Answer: Less than
18.The thrust produced by turbojet engine first _____________ and then ______________ with increasing compressor pressure ratio.
Answer: Increases , Decreases
19.Propulsion efficiency of a jet engine is ____________ proportional to the thrust power and ________________proportional to the air mass flow rate
Answer: Directly, Inversely
20.thrust available from a turbojet engine _______________ as altitude increases
Answer: Decreases.