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

1. For speed above 3000 km/hour, it is more advantageous to use
A. Turbojet engine
B. Ramjet engine
C. Propellers
D. Rockets
Answer : B

2. The thermodynamic efficiency of rotary compressor is based on
A. Isothermal compression
B. Adiabatic compression
C. Isentropic compression
D. Polytropic compression
Answer : B

3. Which of the following statement is correct relating to rocket engines?
A. The combustion chamber in a rocket engine is directly analogous to the reservoir of a supersonic wind tunnel
B. The stagnation conditions exist at the combustion chamber
C. The exit velocities of exhaust gases are much higher than those in jet engine
D. All of the above
Answer : D

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

5. Out of the following, from where you will prefer to take intake for air compressor
A. From an air conditioned room maintained at 20°C
B. From outside atmosphere at 1°C
C. From coal yard side
D. From a side where cooling tower is located nearby
Answer : D

6. For a two stage reciprocating compressor, compression from p? to p? is with perfect intercooling and no pressure losses. If compression in both the cylinders follows the same polytropic process and the atmospheric pressure is pa, then the intermediate pressure p? is given by
A. p? = (p? + p?)/2
B. p? = p?. p?
C. P? = Pa × p?/p?
D. p? = Pa p?/p?
Answer : B

7. The material commonly used for air craft gas turbine is
A. Stainless steel
B. High alloy steel
C. Duralumin
D. Timken, Haste alloys
Answer : D

8. High air-fuel ratio in gas turbines
A. Increases power output
B. Improves thermal efficiency
C. Reduces exhaust temperature
D. Do not damage turbine blades
Answer : C

9. A closed cycle gas turbine works on
A. Carnot cycle
B. Rankine cycle
C. Ericsson cycle
D. Joule cycle
Answer : D

10. 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

11. The air power of the compressor is also known as
A. Indicated power
B. Brake power
C. Frictional power
D. None of these
Answer : A

12. 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

13. 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

14. 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

15. 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

16. The volume of air delivered by the compressor is called
A. Free air delivery
B. Compressor capacity
C. Swept volume
D. None of these
Answer : B

17. 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

18. 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

19. 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

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

21. 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

22. 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

23. The ratio of work done per cycle to the swept volume in case of compressor is called
A. Compression index
B. Compression ratio
C. Compressor efficiency
D. Mean effective pressure
Answer : D

24. 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

25. 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

26. The mass of gas turbine per kW developed is about ________ as that of an I.C. engine.
A. Same
B. One-half
C. One fourth
D. One sixth
Answer : D

27. Inter-cooling in multistage compressors is done
A. To cool the air during compression
B. To cool the air at delivery
C. To enable compression in two stages
D. To minimise the work of compression
Answer : D

28. 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

29. 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

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

31. The overall isothermal efficiency of the compressor is defined as the ratio of
A. Work required to compress the air isothermally to the actual work required to compress the air for the same pressure ratio
B. Isothermal power to the shaft power or B.P. of the motor or engine required to drive the compressor
C. Volume of free air delivery per stroke to the swept volume of the piston
D. Isentropic power to the power required to drive the compressor
Answer : B

32. 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

33. 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

34. 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

35. 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

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

37. The pressure ratio in gas turbines is of the order of
A. 2 : 1
B. 4 :1
C. 61 : 1
D. 9 : 1
Answer : C

38. 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

39. 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

40. 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

41. In a centrifugal compressor, the highest Mach number leading to shock wave in the fluid flow occurs at
A. Diffuser inlet radius
B. Diffuser outlet radius
C. Impeller inlet radius
D. Impeller outlet radius
Answer : B

42. A closed cycle gas turbine gives ________ efficiency as compared to an open cycle gas turbine.
A. Same
B. Lower
C. Higher
D. None of these
Answer : C

43. 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

44. 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

45. 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

46. 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

47. Euler's equation is applicable for
A. Centrifugal compressor
B. Axial compressor
C. Pumps
D. All of the above
Answer : D

48. 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

49. Axial flow compressor resembles
A. Centrifugal pump
B. Reciprocating pump
C. Turbine
D. Sliding vane compressor
Answer : C

50. 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