Compressors, Gas Turbines & Jet Engines MCQ Solved Paper for RRB NTPC

1. Pressure ratio in gas turbines is the ratio of
A. Compressor pressure ratio
B. Highest pressure to exhaust pressure
C. Inlet pressure to exhaust pressure
D. Pressures across the turbine
Answer : B

2. Volumetric efficiency is
A. The ratio of stroke volume to clearance volume
B. The ratio of the air actually delivered to the amount of piston displacement
C. Reciprocal of compression ratio
D. Index of compressor performance
Answer : B

3. 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

4. In multistage compressor, the isothermal compression is achieved by
A. Employing intercooler
B. By constantly cooling the cylinder
C. By running compressor at very slow speed
D. By insulating the cylinder
Answer : C

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

6. 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

7. The closed cycle in gas turbines
A. Provides greater flexibility
B. Provides lesser flexibility
C. In never used
D. Is used when gas is to be burnt
Answer : A

8. Propulsion efficiency of the following order is obtained in practice
A. 34 %
B. 50 %
C. 60 %
D. 72 %
Answer : C

9. In a centrifugal compressor, the ratio of the ________ to the blade velocity is called slip factor.
A. Inlet whirl velocity
B. Outlet whirl velocity
C. Inlet velocity of flow
D. Outlet velocity of flow
Answer : D

10. The criterion of the thermodynamic efficiency for rotary compressor is
A. Isentropic compression
B. Isothermal compression
C. Polytropic compression
D. None of the above
Answer : A

11. The net work input required for compressor with increase in clearance volume
A. Increases
B. Decreases
C. Remains same
D. Increases/decreases depending on compressor capacity
Answer : C

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

13. The power available for takeoff and climb in case of turbojet engine as compared to reciprocating engine is
A. Less
B. More
C. Same
D. May be less or more depending on ambient conditions
Answer : A

14. The ratio of the discharge pressure to the inlet pressure of air is called
A. Compression ratio
B. Expansion ratio
C. Compressor efficiency
D. Volumetric efficiency
Answer : A

15. In a four stage compressor, if the pressure at the first and third stage is 1 bar and 16 bar, then the delivery pressure at the fourth stage will be
A. 1 bar
B. 16 bar
C. 64 bar
D. 256 bar
Answer : C

16. 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

17. A compressor at high altitude will draw
A. More power
B. Less power
C. Same power
D. More/less power depending on other factors
Answer : B

18. 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

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

20. The propulsive power of the rocket is (where v? = Jet velocity, and v? = Aircraft velocity)
A. (v?² -v?²)/2g
B. (v? - v?)²/2g
C. (v?² -v?²)/g
D. (v? - v?)²/g
Answer : A

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

22. Free air is the air at
A. Atmospheric conditions at any specific location
B. 20°C and 1 kg/cm² and relative humidity of 36%
C. 0°C and standard atmospheric conditions
D. 15°C and 1 kg/cm²
Answer : A

23. The following is true for an open cycle gas turbine having exhaust heat exchanger. Atmospheric air before entering the compressor is
A. Heated
B. Compressed air before entering the combustion chamber is heated
C. Bled gas from turbine is heated and readmitted for complete expansion
D. Exhaust gases drive the compressor
Answer : B

24. The work ratio of a gas turbine plant is defined as the ratio of
A. Net work output and heat supplied
B. Net work output and work done by turbine
C. Actual heat drop and isentropic heat drop
D. Net work output and isentropic heat drop
Answer : B

25. A jet engine has
A. No propeller
B. Propeller in front
C. Propeller at back
D. Propeller on the top
Answer : A

26. Efficiency of gas turbine is increased by
A. Reheating
B. Inter cooling
C. Adding a regenerator
D. All of the above
Answer : C

27. 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

28. The ratio of isentropic work to Eulers work is known as
A. Compressor efficiency
B. Isentropic efficiency
C. Euler's efficiency
D. Pressure coefficient
Answer : D

29. 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

30. 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

31. 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

32. The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as
A. Compressor efficiency
B. Volumetric efficiency
C. Isothermal efficiency
D. Mechanical efficiency
Answer : B

33. 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

34. 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

35. 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

36. 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

37. 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

38. In turbo fan engine, the jet velocity as compared to turbojet engine is
A. Less
B. More
C. Same
D. May be less or more depending upon speed
Answer : A

39. The thrust of a jet propulsion power unit can be increased by
A. Injecting water into the compressor
B. Burning fuel after gas turbine
C. Injecting ammonia into the combustion chamber
D. All of the above
Answer : D

40. There is a certain pressure ratio (optimum) for a gas turbine at which its thermal efficiency is maximum. With increase in turbine temperature, the value of pressure ratio for the peak efficiency would
A. Remain same
B. Decrease
C. Increase
D. None of the above
Answer : C

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

42. Atmospheric pressure is 1.03 kg/cm and vapour pressure is 0.03 kg/cm. The air pressure will be
A. 1.03 kg/cm²
B. 1.06 kg/cm²
C. 1.00 kg/cm²
D. 0.53 kg/cm²
Answer : C

43. During base load operation, the best method of controlling compressor is
A. Start-stop motor
B. Constant speed unloader
C. Relief valve
D. Variable speed
Answer : A

44. A rotary compressor is driven by an
A. Electric motor
B. Engine
C. Either (A) or (B)
D. None of these
Answer : C

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

46. To avoid moisture troubles, the branch connections from compressed air lines should be taken from
A. Top side of main
B. Bottom side of main
C. Left side of main
D. Right side of main
Answer : A

47. The efficiency and work ratio of a gas turbine plant can be increased by
A. Adding heat exchanger
B. Injecting water in/around combustion chamber
C. Reheating the air after partial expansion in the turbine
D. All of the above
Answer : D

48. 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

49. 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

50. 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