LIC AAO - Compressors, Gas Turbines & Jet Engines 1000+ MCQ [Solved] PDF Download

1. Pick up the correct statement
A. Large gas turbines use radial inflow turbines
B. Gas turbines have their blades similar to steam turbine
C. Gas turbine's blade will appear as impulse section at the hub and as a reaction section at tip
D. Gas turbines use both air and liquid cooling
Answer : C

2. The overall efficiency of the compressed air system is the
A. Ratio of shaft output of the air motor to the shaft input to the compressor
B. Ratio of shaft input to the compressor to the shaft output of air motor
C. Product of shaft output of air motor and shaft input to the compressor
D. None of the above
Answer : A

3. In open cycle turbojet engines used in military aircraft, reheating the exhaust gas from the turbine by burning, more fuel is used to increase the
A. Thrust and range of aircraft
B. Efficiency of the engine
C. Both (A) and (B)
D. None of these
Answer : A

4. If the flow of air through the compressor is parallel to its axis, then the compressor is
A. Reciprocating compressor
B. Centrifugal compressor
C. Axial flow compressor
D. Turbo compressor
Answer : C

5. In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to
A. N.T.P. conditions
B. Intake temperature and pressure conditions
C. 0°C and 1 kg/cm²
D. 20°C and 1 kg/cm²
Answer : B

6. Euler's equation is applicable for
A. Centrifugal compressor
B. Axial compressor
C. Pumps
D. All of the above
Answer : D

7. If p?, is the pressure of air entering the L.P. cylinder and p? is the pressure of air leaving the L.P. cylinder (or intercooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where D? = Dia. of L.P. cylinder, and D? = Dia. of H.P. cylinder)
A. D?/D? = p? p?
B. D?/D? = p?/p?
C. D?/D? = p?/p?
D. None of these
Answer : C

8. The capacity of a compressor is 5 m /min refers to
A. Standard air
B. Free air
C. Compressed air
D. Compressed air at delivery pressure
Answer : B

9. Ratio of indicated h.p. to shaft h.p. in known as
A. Compressor efficiency
B. Isothermal efficiency
C. Volumetric efficiency
D. Mechanical efficiency
Answer : D

10. The degree of reaction of an axial flow turbine is the ratio of isentropic temperature drop in a blade row to the
A. Adiabatic temperature drop in the stage
B. Total temperature drop
C. Total temperature drop in the stage
D. Total adiabatic temperature drop
Answer : C

11. Surging is the phenomenon of
A. Air stream blocking the passage
B. Motion of air at sonic velocity
C. Unsteady, periodic and reversed flow
D. Air stream not able to follow the blade contour
Answer : C

12. For maximum work, the reheating should be done to an intermediate pressure of (Where p? = Maximum pressure, and p? = Minimum pressure)
A. (p? - p?)/2
B. (p? + p?)/2
C. p?/p?
D. p? p?
Answer : D

13. In air breathing jet engine, the jet is formed by expanding
A. Highly heated atmospheric air
B. Solids
C. Liquid
D. Plasma
Answer : A

14. Pick up wrong statement. Surging phenomenon in centrifugal compressor depends on
A. Mass flow rate
B. Pressure ratio
C. Change in load
D. Stagnation pressure at the outlet
Answer : D

15. Work ratio of a gas turbine may be improved by
A. Decreasing the compression work
B. Increasing the compression work
C. Increasing the turbine work
D. Both (A) and (C) above
Answer : D

16. The inlet pressure is always ________ the discharge pressure.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : B

17. Volumetric efficiency of a compressor with clearance volume
A. Increases with increase in compression ratio
B. Decreases with increase in compression ratio
C. In not dependent upon compression ratio
D. May increase/decrease depending on compressor capacity
Answer : B

18. The degree of reaction in an axial flow compressor is defined as the ratio of static enthalpy rise in the
A. Rotor to static enthalpy rise in the stator
B. Stator to static enthalpy rise in the rotor
C. Rotor to static enthalpy rise in the stage
D. Stator to static enthalpy rise in the stage
Answer : C

19. Rotary compressors are used for delivering
A. Small quantities of air at high pressures
B. Large quantities of air at high pressures
C. Small quantities of air at low pressures
D. Large quantities of air at low pressures
Answer : D

20. The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is
A. Pressure drop across the valves
B. Superheating in compressor
C. Clearance volume and leakages
D. All of these
Answer : D

21. The work done per unit mass of air in compression will be least when n is equal to
A. 1
B. 1.2
C. 1.3
D. 1.4
Answer : A

22. The axial flow compressor is preferred in aircraft gas turbines because of
A. Low frontal area
B. Higher thrust
C. High pressure rise
D. None of these
Answer : A

23. The degree of reaction is usually kept ________ for all types of axial flow compressors.
A. 0.2
B. 0.3
C. 0.4
D. 0.5
Answer : D

24. The ratio of the net work obtained from the gas turbine plant to the turbine work is known as
A. Compression ratio
B. Work ratio
C. Pressure ratio
D. None of these
Answer : B

25. Losses in a centrifugal compressor are due to
A. Inlet losses
B. Impeller channel losses
C. Diffuser losses
D. All of the above
Answer : D

26. What will be the volume of air at 327°C if its volume at 27°C is 1.5 m³/ mt?
A. 3 m³/ mt.
B. 1.5 m³/ mt.
C. 18 m³/ mt.
D. 6 m³/ mt.
Answer : A

27. For perfect intercooling in a two stage compressor
A. p?/p? = p?/p?
B. p?/p? = p?/p?
C. p? = p?
D. p? = p? p?
Answer : A

28. The minimum work required for a three stage reciprocating air compressor is ________ the work required for each stage.
A. Equal to
B. Double
C. Three times
D. Six times
Answer : C

29. Separators in compressor installations are located
A. Before intercooler
B. After intercooler
C. After receiver
D. Between after-cooler and air receiver
Answer : D

30. The temperature of air at the beginning of the compression stroke is ________ the atmospheric temperature.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

31. The stagnation pressure rise in a centrifugal compressor takes place
A. In the diffuser only
B. In the impeller only
C. In the diffuser and impeller
D. In the inlet guide vanes only
Answer : C

32. The air entry velocity m a rocket as compared to aircraft is
A. Same
B. More
C. Less
D. Zero
Answer : D

33. Diffuser in a compressor is used to
A. Increase velocity
B. Make the flow streamline
C. Convert pressure energy into kinetic energy
D. Convert kinetic energy into pressure energy
Answer : D

34. In the cross compounding of the gas turbine plant
A. H.P. compressor is connected to H.P. turbine and L.P. compressor to L.P. turbine
B. H.P. compressor is connected to L.P. turbine and L.P. compressor is connected to H.P. turbine
C. Both the arrangements can be employed
D. All are connected in series
Answer : B

35. Stalling of blades in axial flow compressor is the phenomenon of
A. Air stream blocking the passage
B. Motion of air at sonic velocity
C. Unsteady periodic and reversed flow
D. Air stream not able to follow the blade contour
Answer : D

36. For minimum work required to compress and deliver a quantity of air by multistage compression
A. The compression ratio in each stage should be same
B. The intercooling should be perfect
C. The workdone in each stage should be same
D. All of the above
Answer : D

37. Pick up the correct statement
A. Gas turbine uses low air-fuel ratio to economise on fuel
B. Gas turbine uses high air-fuel ratio to reduce outgoing temperature
C. Gas turbine uses low air-fuel ratio to develop the high thrust required
D. All of the above
Answer : B

38. In a centrifugal compressor, the highest Mach number leading to shock wave in the fluid flow occurs at
A. Diffuser inlet radius
B. Diffuser outlet radius
C. Impeller inlet radius
D. Impeller outlet radius
Answer : B

39. Gas turbine as compared to internal combustion engine
A. Can be driven at a very high speed
B. Produces uniform torque
C. Has more efficiency
D. All of these
Answer : D

40. The absolute pressure of air at the outlet of a compressor is called
A. Back pressure
B. Critical pressure
C. Discharge pressure
D. None of these
Answer : C

41. Maximum work is done in compressing air when the compression is
A. Isothermal
B. Adiabatic
C. Polytropic
D. None of the above
Answer : B

42. When the outlet angle from the rotor of a centrifugal compressor is more than 90°, then the blades are said to be
A. Forward curved
B. Backward curved
C. Radial
D. None of these
Answer : A

43. In the axial flow gas turbine, the work ratio is the ratio of
A. Compressor work and turbine work
B. Output and input
C. Actual total head temperature drop to the isentropic total head drop from total head inlet to static head outlet
D. Actual compressor work and theoretical compressor work
Answer : C

44. The weight per horse power ratio for gas in Turbine as compared to I.C. engine and steam turbine is
A. Same
B. Higher
C. Lower
D. None of these
Answer : C

45. The volumetric efficiency of compressor with increase in compression ratio will
A. Increase
B. Decrease
C. Remain same
D. May increase or decrease depending on clearance volume
Answer : B

46. The gas in cooling chamber of a closed cycle gas turbine is cooled at
A. Constant volume
B. Constant temperature
C. Constant pressure
D. None of these
Answer : C

47. The pressure and temperature conditions of air at the suction of compressor are
A. Atmospheric
B. Slightly more than atmospheric
C. Slightly less than atmospheric
D. Pressure slightly less than atmospheric and temperature slightly more than atmospheric
Answer : D

48. The compressor performance at higher altitude compared to sea level will be
A. Same
B. Higher
C. Lower
D. Dependent on other factors
Answer : C

49. A machine used to raise the pressure of air is called
A. Gas turbine
B. I.C engine
C. Compressor
D. Air motor
Answer : C

50. In jet engines, paraffin is usually used as the fuel because of its
A. High calorific value
B. Ease of atomisation
C. Low freezing point
D. Both (A) and (C) above
Answer : D