Aerospace Propulsion - I Mid - II, November - 2014

1.Air (Cp = 1 kJ/kg, = 1.4) enters a compressor at a temperature of 270 C. The compressor pressure ratio is assuming an efficiency of 80%, the compressor work required in kJ/kg is
  • 160
  • 172
  • 182
  • 225
Answer: C
2.Consider an ideal axial turbine in which air (Cp = 1.005 kJ/kg, = 1.4) enters at total temperature 700 K and leaves at axial speed 300 m/s and temperature 300 K. The work extracted per unit mass flow rate is
  • 357 kJ/kg
  • 447 kJ/kg
  • 960 kJ/kg
  • 492 kJ/kg
Answer: A
3.If r, θ and x denote the radial, tangential and axial directions respectively, then the quantity that remains conserved in an ideal centrifugal compressor (impeller) is where, h0rel is the total enthalpy relative to the impeller blades.
  • h0 + 2uc
  • h0rel + 1/2 u2
  • h + 1/2(u2 + c2)
  • h0rel - 1/2 u2
Answer: D
4.For free vortex design, which of these are true?
  • Stagnation enthalpy h0 = constant
  • Entropy S = constant
  • r V = constant, vz = constant
  • All of the above
Answer: D
5.In the combustion chamber of a jet engine, the CO2 emission in the diffusion flame is maximum at an equivalence ratio (Φ) with value equal to
  • 0.7
  • 0.2
  • 0.75
  • 0.9
Answer: C
6.Which one of the following materials should be selected to design an axial flow turbine operating at high temperatures?
  • Steel alloy
  • Titanium alloy
  • Nickel alloy
  • Aluminum alloy
Answer: C
7.Which one of the following statement is true?
  • The isentropic efficiency of a compressor is constant throughout the compressor
  • Flow separation problems are more critical for the axial compressors than for the centrifugal compressors
  • The pressure ratio of a centrifugal compressor approaches zero as the compressor mass flow rate approaches zero
  • Centrifugal compressors are always designed with multiple stages
Answer: A
8.The division of feed air to an aircraft gas turbine combustor into primary and secondary stream serves which of the following purposes?
  • A flammable mixture can be formed
  • Cooling of combustor liner and flame tube cannot be accomplished
  • Specific fuel consumption can be reduced
  • None of the above
Answer: A
9.For compressor, what is the relation between polytropic efficiency (p) and overall efficiency (o)?
  • p = o
  • p > o
  • p < o
  • None of these
Answer: B
10.For turbine, what is the relation between polytropic efficiency (p) and overall efficiency (o)?
  • p = o
  • p > o
  • p < o
  • None of these
Answer: C
11.For a multi stage axial flow compressor with constant diameter hub, blade height ____________ in the flow direction.
Answer: Decreases
12.The maximum operating flow rate through a centrifugal compressor at a given RPM is limited by- _________________ of diffuser throat.
Answer: Choking
13.The degree of reaction of an __________________turbine is zero.
Answer: Impulse
14.The purpose of a ________________ in the combustor is to convert the bulk fuel into tiny droplets.
Answer: Fuel injection system
15.In the context of flow compressor, for rotor, and stator, ________________ is constant.
Answer: Enthalpy
16.Combustor efficiency of an aircraft engine _______________with altitude.
Answer: Increases
17.______________ remains constant across a centrifugal compressor.
Answer: Rothalpy
18.The specific speed of a centrifugal compressor is generally independent of the ___________ of compressor but depends only on the __________ of the compressor.
Answer: Type , Size
19.In a scramjet engine, the Mach number at the entry to the combustion chamber is around ___________.
Answer: 2
20.A gas turbine engine is mounted on an aircraft which can attain a maximum altitude of 11km from sea level. The combustor volume of this engine is decided based on conditions at ______________ altitude.
Answer: 11 km