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

1. 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

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

3. 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

4. In air compressors, free air delivery means the
A. Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B. Volume of air delivered by the compressor
C. Volume of air sucked by the compressor during its suction stroke
D. None of the above
Answer : A

5. 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

6. 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

7. If the clearance ratio for a reciprocating air compressor is 'K', then its volumetric efficiency is given by
A. 1 - k + k (p?/p?)^1/n
B. 1 + k - k (p?/p?)^1/n
C. 1 - k + k (p?/p?) ^{n- 1/n}
D. 1 + k - k (p?/p?) ^n-1/n
Answer : B

8. In an axial flow compressor, the ratio of pressure in the rotor blades to the pressure rise in the compressor in one stage is known as
A. Work factor
B. Slip factor
C. Degree of reaction
D. Pressure coefficient
Answer : C

9. 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

10. 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

11. 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

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. 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

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

15. 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

16. 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

17. 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

18. A rocket engine for the combustion of its fuel
A. Carries its own oxygen
B. Uses surrounding air
C. Uses compressed atmospheric air
D. Does not require oxygen
Answer : A

19. 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

20. In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into
A. Atmosphere
B. Vacuum
C. Discharge nozzle
D. Back to the compressor
Answer : C

21. The inlet pressure is always ________ the discharge pressure.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : B

22. In jet engines, for the efficient production of large power, fuel is burnt in an atmosphere of
A. Vacuum
B. Atmospheric air
C. Compressed air
D. Oxygen alone
Answer : C

23. 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

24. Clearance volume in actual reciprocating compressors is essential
A. To accommodate Valves in the cylinder head
B. To provide cushioning effect
C. To attain high volumetric efficiency
D. To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head
Answer : D

25. The compressor capacity is defined as the
A. Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B. Volume of air delivered by the compressor
C. Volume of air sucked by the compressor during its suction stroke
D. None of the above
Answer : B

26. In the aircraft propellers
A. The propulsive matter is caused to flow around the propelled body
B. Propulsive matter is ejected from within the propelled body
C. Its functioning does not depend on presence of air
D. All of the above
Answer : D

27. 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

28. Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is
A. Higher
B. Lower
C. Equal
D. Cant be compared
Answer : B

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. 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

31. 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

32. 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

33. Ram compression in turbojet involves
A. Reduction of speed of incoming air and conversion of part of it into pressure energy
B. Compression of inlet air
C. Increasing speed of incoming air
D. Lost work
Answer : A

34. 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

35. The air is delivered ________ in one revolution in case of a three lobbed rotor.
A. Two times
B. Three times
C. Four times
D. Six times
Answer : D

36. The maximum delivery pressure in a rotary air compressor is
A. 10 bar
B. 20 bar
C. 30 bar
D. 50 bar
Answer : A

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

38. 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

39. 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

40. 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

41. 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

42. Compression efficiency is compared against
A. Ideal compression
B. Adiabatic compression
C. Isentropic compression
D. Isothermal compression
Answer : D

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

44. Standard air is the air at ________ and relative humidity of 36 percent.
A. 0.1 bar and 20°C
B. 1 bar and 20°C
C. 0.1 bar and 40°C
D. 1 bar and 40°C
Answer : B

45. 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

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

47. If p? is the pressure of air entering the L.P, cylinder and p? is the pressure of air leaving the H.P. cylinder, then the ratio of cylinder diameters for a single acting, two stage reciprocating compressor with complete intercooling is given by
A. D?/D? = (p? p?)^1/2
B. D?/D? = (p?/p?)^1/4
C. D?/D? = (p? p?)^1/4
D. D?/D? = (p?/p?)^1/4
Answer : D

48. It is not possible to use closed gas turbine cycle in aeronautical engines because
A. It is inefficient
B. It is bulky
C. It requires cooling water for its operation
D. None of the above
Answer : C

49. 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

50. 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