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

1. 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

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

3. 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

4. Gas turbines for power generation are normally used
A. To supply base load requirements
B. To supply peak load requirements
C. To enable start thermal power plant
D. In emergency
Answer : B

5. A rocket works with maximum overall efficiency when air craft velocity is equal to the
A. Jet velocity
B. Twice the jet velocity
C. Half the jet velocity
D. Average of the jet velocity
Answer : C

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 assumption made in two stage compression with intercooler is that
A. There is no pressure drop in the intercooler
B. The compression in both the cylinders is polytropic
C. The suction and delivery of air takes place at constant pressure
D. All of the above
Answer : D

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

9. Gas turbines use following type of air compressor
A. Centrifugal type
B. Reciprocating type
C. Lobe type
D. Axial flow type
Answer : D

10. When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is ________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : A

11. The thermal efficiency of a simple gas turbine for a given turbine inlet temperature with increase in pressure ratio
A. Increases
B. Decreases
C. First increases and then decreases
D. First decreases and then increases
Answer : A

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

13. 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

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

15. 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

16. 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

17. Which is false statement about air receivers?
A. These are used to dampen pulsations
B. These act as reservoir to take care of sudden demands
C. These increase compressor efficiency
D. These knock out some oil and moisture
Answer : C

18. A compressor at high altitudes will require ________ power.
A. Same
B. Less
C. More
D. None of these
Answer : B

19. The volumetric efficiency of a compressor falls roughly as follows for every 100 m increase in elevation
A. 0.1 %
B. 0.5 %
C. 1.0 %
D. 5 %
Answer : C

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

21. 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

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

23. 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

24. In a high pressure compressor, the delivery pressure is
A. 1 to 5 bar
B. 5 to 8 bar
C. 8 to 10 bar
D. 10 to 15 bar
Answer : C

25. An ideal air compressor cycle with clearance on PV diagram can be represented by following processes
A. One adiabatic, two isobaric, and one constant volume
B. Two adiabatic and two isobaric
C. Two adiabatic, one isobaric and one constant volume
D. One adiabatic, one isobaric and two constant volumes
Answer : B

26. 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

27. 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

28. For a two stage compressor, if index of compression for higher stage is greater than index of compression for lower stage, then the optimum pressure as compared to ideal case will
A. Increase
B. Decrease
C. Remain unaffected
D. Other factors control it
Answer : A

29. 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

30. 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

31. The compressed air may be used
A. In gas turbine plants
B. For operating pneumatic drills
C. In starting and supercharging of I.C. engines
D. All of the above
Answer : D

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

33. 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

34. 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

35. 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

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

37. In axial flow compressor, exit flow angle deviation from the blade angle is a function of
A. Blade camber
B. Blade camber and incidence angle
C. Spacechord ratio
D. Blade camber and spacechord ratio
Answer : B

38. 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

39. Reheating in multistage expansion gas turbine results in
A. High thermal efficiency
B. Reduction in compressor work
C. Decrease of heat loss in exhaust
D. Maximum work output
Answer : D

40. 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

41. 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

42. 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

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

44. 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

45. Pick up the wrong statement
A. Centrifugal compressors deliver practically constant pressure over a considerable range of capacities
B. Axial flow compressors have a substantially constant delivery at variable pressures
C. Centrifugal compressors have a wider stable operating range than axial flow compressors
D. Axial flow compressors are bigger in diameter compared to centrifugal type
Answer : D

46. An air compressor may be controlled by
A. Throttle control
B. Clearance control
C. Blow off control
D. Any one of the above
Answer : D

47. 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

48. 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

49. 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

50. In a closed cycle gas turbine, the air is compressed
A. Isothermally
B. Polytropically
C. Isentropically
D. None of these
Answer : C