Compressors, Gas Turbines & Jet Engines MCQ Solved Paper for LIC ADO

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

2. 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

3. 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

4. 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

5. The velocity of air entering in a rocket is ________ as compared to an aircraft.
A. Zero
B. Less
C. More
D. Same
Answer : A

6. Mechanical efficiency of gas turbines as compared to I.C engines is
A. Higher
B. Lower
C. Same
D. None of the above
Answer : A

7. The compressor efficiency is the
A. Isothermal H.P/indicated H.R
B. Isothermal H.P./shaft H.R
C. Total output/air input
D. Compression work/motor input
Answer : A

8. 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

9. 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

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

11. For minimum work required to compress and deliver a quantity of air by multistage compression
A. The compression ratio in each stage should be same
B. The intercooling should be perfect
C. The workdone in each stage should be same
D. All of the above
Answer : D

12. 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

13. 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

14. The performance of air compressor at high altitudes will be ________ as compared to that at sea level.
A. Same
B. Lower
C. Higher
D. None of these
Answer : B

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

16. 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

17. 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

18. 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

19. 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

20. Gas turbine as compared to internal combustion engine
A. Can be driven at a very high speed
B. Produces uniform torque
C. Has more efficiency
D. All of these
Answer : D

21. 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

22. Isothermal compression efficiency can be attained by running the compressor
A. At very high speed
B. At very slow speed
C. At average speed
D. At zero speed
Answer : B

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

24. 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

25. 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

26. For minimum work in multistage compression, assuming same index of compression in all stages
A. Work done in first stage should be more
B. Work done in subsequent stages should increase
C. Work done in subsequent stages should decrease
D. Work done in all stages should be equal
Answer : D

27. 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

28. 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

29. 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

30. 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

31. 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. V_i = V_o
B. V_t > V_o
C. U < V_o
D. V = U_o
Answer : A

32. 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

33. 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

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

35. Losses in a centrifugal compressor are due to
A. Inlet losses
B. Impeller channel losses
C. Diffuser losses
D. All of the above
Answer : D

36. Inter cooling in compressors
A. Cools the delivered air
B. Results in saving of power in compressing a given volume to given pressure
C. Is the standard practice for big compressors
D. Enables compression in two stages
Answer : B

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

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

39. The mean effective pressure of the compressor is 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 : D

40. 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

41. 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

42. 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

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

44. In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to
A. N.T.P. conditions
B. Intake temperature and pressure conditions
C. 0°C and 1 kg/cm²
D. 20°C and 1 kg/cm²
Answer : B

45. In jet propulsion power unit, the inlet duct of diverging shape is used in order to
A. Collect more air
B. Convert kinetic energy of air into pressure energy
C. Provide robust structure
D. Beautify the shape
Answer : B

46. 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

47. 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

48. 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

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

50. 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