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1000+ Compressors, Gas Turbines & Jet Engines MCQ for FCI Recruitment [Solved]

Thursday 9th of March 2023

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1. 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
2. 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
3. Actual compression curve is
A. Same as isothermal
B. Same as adiabatic
C. Better than isothermal and adiabatic
D. In between isothermal and adiabatic
Answer : D
4. Reheating in gas turbine results in
A. Increase of work ratio
B. Decrease of thermal efficiency
C. Decrease of work ratio
D. Both (A) and (B) above
Answer : D
5. Intercooling in gas turbines
A. Decreases net output but increases thermal efficiency
B. Increases net output but decreases thermal efficiency
C. Decreases net output and thermal efficiency both
D. Increases net output and thermal efficiency both
Answer : D
6. The volume of air sucked by the compressor during its suction stroke is called
A. Free air delivery
B. Compressor capacity
C. Swept volume
D. None of these
Answer : C
7. 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
8. Only rocket engines can be propelled to space because
A. They can generate very high thrust
B. They have high propulsion efficiency
C. These engines can work on several fuels
D. They are not air breathing engines
Answer : D
9. 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
10. Propulsion efficiency of the following order is obtained in practice
A. 34 %
B. 50 %
C. 60 %
D. 72 %
Answer : C
11. 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
12. 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
13. 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
14. The overall isothermal efficiency of compressor is defined as the ratio of
A. Isothermal h.p. to the BHP of motor
B. Isothermal h.p. to adiabatic h.p.
C. Power to drive compressor to isothermal h.p.
D. Work to compress air isothermally to work for actual compression
Answer : A
15. 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
16. The blades of gas turbine are made of
A. High nickel alloy
B. Stainless steel
C. Carbon steel
D. High alloy steel
Answer : A
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. 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
19. The volumetric efficiency of a compressor falls roughly as follows for every 5°C increase in atmospheric temperature
A. 0.1 %
B. 0.5 %
C. 1 %
D. 5 %
Answer : C
20. 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. Vi = Vo
B. Vt > Vo
C. U < Vo
D. V = Uo
Answer : A
21. When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is ________ the original atospheric 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
22. 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
23. 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
24. The intercooler pressure, for minimum work required, for a two stage reciprocating air compressor, is given by (where p? = Intake pressure of air, p? = Intercooler pressure, and p? = Delivery pressure of air)
A. p? = p? × p?
B. p? = p?/p?
C. p? = p? × p?
D. p? = p?/p?
Answer : C
25. Maximum work is done in compressing air when the compression is
A. Isothermal
B. Adiabatic
C. Polytropic
D. None of the above
Answer : B
26. Maximum temperature in a gas turbine is of the order of
A. 700°C
B. 2000°C
C. 1500°C
D. 1000°C
Answer : A
27. 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
28. 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
29. 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
30. 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
31. 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
32. Inter-cooling in gas turbine results in
A. Increase in net output but decrease in thermal efficiency
B. Increase in thermal efficiency but decrease in net output
C. Increase in both thermal efficiency and net output
D. Decrease in both thermal efficiency and net output
Answer : A
33. 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
34. 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
35. The pressure of air at the beginning of the compression stroke is ________ the atmospheric pressure.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : B
36. 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
37. Open cycle gas turbine works on
A. Brayton or Atkinson cycle
B. Rankine cycle
C. Carnot cycle
D. Erricson cycle
Answer : A
38. In gas turbines, high thermal efficiency is obtained in
A. Closed cycle
B. Open cycle
C. Both of the above
D. Closed/open depending on other considerations
Answer : A
39. Pick up the correct statement
A. Closed cycle gas turbine is an I.C engine
B. Gas turbine uses same working fluid over and over again
C. Ideal efficiency of closed cycle gas turbine plant is more than Carnot cycle efficiency
D. Thrust in turbojet is produced by nozzle exit gases.
Answer : D
40. The air entry velocity m a rocket as compared to aircraft is
A. Same
B. More
C. Less
D. Zero
Answer : D
41. 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
42. The thermodynamic efficiency of rotary compressor is based on
A. Isothermal compression
B. Adiabatic compression
C. Isentropic compression
D. Polytropic compression
Answer : B
43. 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
44. 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
45. For slow speed large capacity compressor, following type of valve will be best suited
A. Poppet valve
B. Mechanical valve of the Corliss, sleeve, rotary or semi rotary type
C. Disc or feather type
D. Any of the above
Answer : C
46. A large clearance volume in a reciprocating compressor results in
A. Reduced volume flow rate
B. Increased volume flow rate
C. Lower suction pressure
D. Lower delivery pressure
Answer : A
47. In a single stage, single acting reciprocating air compressor, without clearance, the workdone on the air during isentropic compression is ________ the heat required to raise the temperature of air from T? to T? at a constant pressure.
A. Equal to
B. Less than
C. Greater than
D. None of these
Answer : A
48. 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
49. More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than
A. 2 kg/cm²
B. 6 kg/cm²
C. 10 kg/cm²
D. 14.7 kg/cm²
Answer : A
50. The velocity of air entering in a rocket is ________ as compared to an aircraft.
A. Zero
B. Less
C. More
D. Same
Answer : A

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