1000+ Compressors, Gas Turbines & Jet Engines Multiple Choice Question Answer [Solved]

1. 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

2. Mining industry usually employs following motive power
A. A.C. electric motor
B. Compressed air
C. Petrol engine
D. Diesel engine
Answer : B

3. Producer gas is produced by
A. Carbonisation of coal
B. Passing steam over incandescent coke
C. Passing air and a large amount of steam over waste coal at about 65°C
D. Partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
Answer : D

4. The clearance volume of the air compressor is kept minimum because
A. It allows maximum compression to be achieved
B. It greatly affects volumetric efficiency
C. It results in minimum work
D. It permits isothermal compression
Answer : B

5. Gas turbine works on
A. Brayton or Atkinson cycle
B. Carnot cycle
C. Rankine cycle
D. Erricson cycle
Answer : A

6. If V, U and Vr represent the absolute velocity of fluid, velocity of blade, and relative velocity of fluid, and suffix I and o stand for entry and exit conditions, then in a rotary machine whose degree of reaction is unity
A. V_i = V_o
B. V_t > V_o
C. U < V_o
D. V = U_o
Answer : A

7. Propulsive efficiency is defined as ratio of
A. Thrust power and fuel energy
B. Engine output and propulsive power
C. Propulsive power and fuel input
D. Thrust power and propulsive power
Answer : D

8. Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is
A. Higher
B. Lower
C. Equal
D. Cant be compared
Answer : B

9. Volumetric efficiency of air compressors is of the order of
A. 20 - 30 %
B. 40 - 50 %
C. 60 - 70 %
D. 70 - 90 %
Answer : D

10. Pick up the false statement
A. Gas turbine is a self starting unit
B. Gas turbine does not require huge quantity of water like steam plant
C. Exhaust losses in gas turbine are high due to large mass flow rate
D. Overall efficiency of gas turbine plant is lower than that of a reciprocating engine
Answer : A

11. Open cycle gas turbine works on
A. Brayton or Atkinson cycle
B. Rankine cycle
C. Carnot cycle
D. Erricson cycle
Answer : A

12. High air-fuel ratio is used in gas turbines
A. To increase the output
B. To increase the efficiency
C. To save fuel
D. To reduce the exit temperature
Answer : D

13. A centrifugal compressor works on the principle of
A. Conversion of pressure energy into kinetic energy
B. Conversion of kinetic energy into pressure energy
C. Centripetal action
D. Generating pressure directly
Answer : B

14. Which of the following statement is wrong?
A. In a two stage reciprocating air compressor with complete intercooling, maximum work is saved.
B. The minimum work required for a two stage reciprocating air compressor is double the work required for each stage.
C. The ratio of the volume of free air delivery per stroke to the swept volume of the piston is called volumetric efficiency.
D. None of the above
Answer : D

15. 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

16. 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

17. 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

18. Which of the following statement is correct as regard to centrifugal compressors?
A. The flow of air is parallel to the axis of the compressor
B. The static pressure of air in the impeller increases in order to provide centripetal force on the air
C. The impeller rotates at high speeds
D. The maximum efficiency is higher than multistage axial flow compressors
Answer : B

19. Maximum delivery pressure is a rotary air compressor is of the order of
A. 6 kg/cm²
B. 10 kg/cm²
C. 16 kg/cm²
D. 25 kg/cm²
Answer : B

20. Gas turbine as compared to steam turbine
A. Requires less space for installation
Has compressor and combustion chamber
C. Has less efficiency
D. All of these
Answer : D

21. The efficiency of a jet engine is higher at
A. Low speeds
B. High speeds
C. Low altitudes
D. High altitudes
Answer : D

22. 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

23. In a single acting reciprocating compressor, the suction, compression and delivery of air takes place in ________ of the piston.
A. One stroke
B. Two strokes
C. Three strokes
D. Four strokes
Answer : B

24. In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into
A. Atmosphere
B. Vacuum
C. Discharge nozzle
D. Back to the compressor
Answer : C

25. It is not possible to use closed gas turbine cycle in aeronautical engines because
A. It is inefficient
B. It is bulky
C. It requires cooling water for its operation
D. None of the above
Answer : C

26. The compression ratio for the compressor is always __________ unity.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

27. A jet engine works on the principle of conservation of
A. Mass
B. Energy
C. Flow
D. Linear momentum
Answer : D

28. The type of rotary compressor used in aeroplanes, is of
A. Centrifugal type
B. Axial flow type
C. Radial flow type
D. None of these
Answer : B

29. 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

30. In a double acting compressor, the air is compressed
A. In one cylinder
B. In two cylinders
C. In a single cylinder on both sides of the piston
D. In two cylinders on both sides of the piston
Answer : C

31. Standard air is the air at ________ and relative humidity of 36 percent.
A. 0.1 bar and 20°C
B. 1 bar and 20°C
C. 0.1 bar and 40°C
D. 1 bar and 40°C
Answer : B

32. The combustion efficiency of a gas turbine using perfect combustion chamber is of the order of
A. 75 %
B. 85 %
C. 90 %
D. 99 %
Answer : D

33. After-cooler is used to
A. Cool the air
B. Decrease the delivery temperature for ease in handling
C. Cause moisture and oil vapour to drop out
D. Reduce volume
Answer : C

34. As the turbine inlet temperature increases, the thermal efficiency of gas turbine for the optimum pressure ratio
A. Increases
B. Decreases
C. Remain same
D. First increases and then decreases
Answer : A

35. 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

36. In a centrifugal compressor, an increase in speed at a given pressure ratio causes
A. Increase in flow
B. Decrease in flow
C. Increase in efficiency
D. Increase in flow and decrease in efficiency
Answer : D

37. Which is false statement about advantages of multistage compressor in comparison to single stage compressor?
A. Less power requirement
B. Better mechanical balance
C. Less loss of air due to leakage past the cylinder
D. Lower volumetric efficiency
Answer : D

38. The indicated work per unit mass of air delivered is
A. Directly proportional to clearance volume
B. Greatly affected by clearance volume
C. Not affected by clearance volume
D. Inversely proportional to clearance volume
Answer : C

39. The thrust on the rotor in a centrifugal compressor is produced by
A. Radial component
B. Axial component
C. Tangential component
D. None of the above
Answer : B

40. In a centrifugal compressor, the flow of air is ________ to the axis of compressor.
A. Parallel
B. Perpendicular
C. Inclined
D. None of these
Answer : B

41. For an irreversible gas turbine cycle, the efficiency and work ratio both depend on
A. Pressure ratio alone
B. Maximum cycle temperature alone
C. Minimum cycle temperature alone
D. Both pressure ratio and maximum cycle temperature
Answer : D

42. The capacity of compressor will be highest when its intake temperature is
A. Lowest
B. Highest
C. Anything
D. Atmospheric
Answer : D

43. The efficiency of roots blower ________ with the increase in pressure ratio.
A. Decreases
B. Increases
C. Does not change
D. None of these
Answer : A

44. In a single acting reciprocating air compressor, without clearance, the compression of air may be
A. Isothermal
B. Polytropic
C. Isentropic
D. Any one of these
Answer : D

45. Clearance volume in actual reciprocating compressors is essential
A. To accommodate Valves in the cylinder head
B. To provide cushioning effect
C. To attain high volumetric efficiency
D. To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head
Answer : D

46. In the aircraft propellers
A. The propulsive matter is caused to flow around the propelled body
B. Propulsive matter is ejected from within the propelled body
C. Its functioning does not depend on presence of air
D. All of the above
Answer : D

47. The output of a gas turbine is 300 KW and its efficiency is 20 percent, the heat supplied is
A. 6000 KW
B. 15 KW
C. 600 KW
D. 150 KW
Answer : B

48. Reheating in a gas turbine
A. Increases the thermal efficiency
B. Increases the compressor work
C. Increases the turbine work
D. Decreases the thermal efficiency
Answer : A

49. Euler's equation can be used for
A. Radial flow compressors
B. Axial flow compressors
C. Pumps
D. All of these
Answer : D

50. The volumetric efficiency of a compressor
A. Increases with decrease in compression ratio
B. Decreases with decrease in compression ratio
C. Increases with increase in compression ratio
D. Decreases with increase in compression ratio
Answer : D