1000+ Compressors, Gas Turbines & Jet Engines MCQ for SSC CGL [Solved]

1. The ratio of specific weight/h.p. of gas turbine and I.C engines may be typically of the order of
A. 1 : 1
B. 2 : 1
C. 4 : 1
D. 1 : 6
Answer : D

2. Isothermal compression efficiency can be attained by running the compressor
A. At very high speed
B. At very slow speed
C. At average speed
D. At zero speed
Answer : B

3. Which is false statement about multistage compression?
A. Power consumption per unit of air delivered is low
B. Volumetric efficiency is high
C. It is best suited for compression ratios around 7:1
D. The moisture in air is condensed in the intercooler
Answer : B

4. Ratio of compression is the ratio of
A. Gauge discharge pressure to the gauge intake pressure
B. Absolute discharge pressure to the absolute intake pressure
C. Pressures at discharge and suction corresponding to same temperature
D. Stroke volume and clearance volume
Answer : B

5. The pressure ratio of an ideal vaned compressor with increase in mass flow rate
A. Increases
B. Decreases
C. Remain constant
D. First decreases and then increases
Answer : C

6. Rotary compressor is best suited for
A. Large quantity of air at high pressure
B. Small quantity of air at high pressure
C. Small quantity of air at low pressure
D. Large quantity of air at low pressure
Answer : B

7. 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

8. A closed gas turbine in which fuel is burnt directly in the air is not possible because of
A. Paucity of O2
B. Increasing gas temperature
C. High specific volume
D. High friction losses
Answer : A

9. Turbofan engine employs
A. One air stream
B. Two or more air streams
C. No air stream
D. Solid fuel firing
Answer : B

10. 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

11. 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

12. The maximum compression ratio in an actual single stage axial flow compressor is of the order of
A. 1 : 1.2
B. 1 : 2
C. 1 : 5
D. 1 : 10
Answer : A

13. The capacity of a compressor is expressed in
A. kg/m²
B. kg/m³
C. m³/min
D. m³/kg
Answer : C

14. The area of actual indicator diagram on an air compressor as compared to area of ideal indicator diagram is
A. Less
B. More
C. Same
D. More/less depending on compressor capacity
Answer : B

15. Adiabatic compression is one in which
A. Temperature during compression remains constant
B. No heat leaves or enters the compressor cylinder during compression
C. Temperature rise follows a linear relationship
D. Work done is maximum
Answer : B

16. The ratio of workdone per cycle to the stroke volume of the compressor is known as
A. Compressor capacity
B. Compression ratio
C. Compressor efficiency
D. Mean effective pressure
Answer : D

17. 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

18. Which one of the following is the effect of blade shape on performance of a centrifugal compressor?
A. Backward curved blades has poor efficiency
B. Backward curved blades lead to stable performance
C. Forward curved blades has higher efficiency
D. Forward curved blades produce lower pressure ratio
Answer : D

19. 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

20. The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called
A. Slip factor
B. Velocity factor
C. Velocity coefficient
D. None of the above
Answer : A

21. The compressor capacity with decrease in suction temperature
A. Increases
B. Decreases
C. Remain unaffected
D. May increase or decrease depending on compressor capacity
Answer : A

22. Which of the following statement is correct?
A. The reciprocating compressors are best suited for high pressure and low volume capacity
B. The effect of clearance volume on power consumption is negligible for the same volume of discharge
C. Both (A) and (B)
D. None of these
Answer : C

23. Choose the correct statement
A. Gas turbine requires lot of cooling water
B. Gas turbine is capable of rapid start up and loading
C. Gas turbines has flat efficiency at part loads
D. Gas turbines have high standby losses and require lot of maintenance
Answer : B

24. To avoid moisture troubles, the compressed air main line should
A. Rise gradually towards the point of use
B. Drop gradually towards the point of use
C. Be laid vertically
D. Be laid exactly horizontally
Answer : B

25. The volumetric efficiency for reciprocating air compressors is about
A. 10 to 40 %
B. 40 to 60 %
C. 60 to 70 %
D. 70 to 90 %
Answer : D

26. 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

27. A turboprop is preferred to turbojet because
A. It has high propulsive efficiency at high speeds
B. It can fly at supersonic speeds
C. It can fly at high elevations
D. It has high power for take off
Answer : D

28. 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

29. Ramjet engine
A. Is self operating at zero flight speed
B. Is not self operating at zero flight speed
C. Requires no air for its operation
D. Produces a jet consisting of plasma
Answer : B

30. 1 m of air at atmospheric condition weighs approximately
A. 0.5 kg
B. 1.0 kg
C. 1.3 kg
D. 2.2 kg
Answer : C

31. 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

32. The velocity of air entering in a rocket is ________ as compared to an aircraft.
A. Zero
B. Less
C. More
D. Same
Answer : A

33. The advantage of multistage compression over single stage compression is
A. Lower power consumption per unit of air delivered
B. Higher volumetric efficiency
C. Decreased discharge temperature
D. All of the above
Answer : D

34. A rocket engine uses ________ for the combustion of its fuel.
A. Surrounding air
B. Compressed atmospheric air
C. Its own oxygen
D. None of these
Answer : C

35. The compression ratio in a gas turbine is of the order of
A. 3.5 : 1
B. 5 : 1
C. 8 : 1
D. 12 : 1
Answer : C

36. The workdone on a compressor will be minimum if air is taken from
A. The atmosphere
B. A source at 0°C
C. A source of low temperature air
D. A source of high temperature air
Answer : C

37. 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

38. Reheating in a multistage expansion gas turbine __________ compressor work.
A. Has no effect on
B. Decreases
C. Increases
D. None of these
Answer : B

39. A gas turbine used in air craft should have
A. High h.p. and low weight
B. Low weight and small frontal area
C. Small frontal area and high h.p.
D. High speed and high h.p
Answer : B

40. Which of the following statement is correct?
A. The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency
B. The compression ratio for the compressor is always greater than unity
C. The compressor capacity is the ratio of workdone per cycle to the stroke volume
D. During isothermal compression of air, the workdone in a compressor is maximum
Answer : B

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

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

43. For supplying intermittent small quantity of air at high pressure, following compressor is best suited
A. Centrifugal
B. Reciprocating
C. Axial
D. Screw
Answer : B

44. The work ratio of simple gas turbine cycle depends on
A. Pressure ratio
B. Maximum cycle temperature
C. Minimum cycle temperature
D. All of the above
Answer : D

45. 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

46. The process, which causes the air to enter the impeller blades of a centrifugal compressor at ________ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.
A. Reduced
B. Increased
C. Zero
D. None of these
Answer : A

47. 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

48. In n? and n? are the indices of compression for the first and second stage of compression, then the ratio of workdone on the first and second stages (W?/W?) with perfect intercooling is given by
A. W?/W? = n?(n? - 1)/n?(n? - 1)
B. W?/W? = n?(n? - 1)/n?(n? - 1)
C. W?/W? = n?/n?
D. W?/W? = n?/n?
Answer : B

49. 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

50. Separators are generally used in air compressor installations
A. Before the intercooler
B. After the intercooler
C. Between the aftercooler and receiver
D. Before first stage suction
Answer : C