Compressors, Gas Turbines & Jet Engines MCQ Solved Paper for UPSC CDS

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

2. Which is false statement about advantages of multistage compressor in comparison to single stage compressor?
A. Less power requirement
B. Better mechanical balance
C. Less loss of air due to leakage past the cylinder
D. Lower volumetric efficiency
Answer : D

3. 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

4. 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

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

6. When the outlet angle from the rotor of a centrifugal compressor is more than 90°, then the blades are said to be
A. Forward curved
B. Backward curved
C. Radial
D. None of these
Answer : A

7. 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

8. 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

9. If infinite number of heaters be used in a gas turbine, then expansion process in turbine approaches
A. Isothermal
B. Isentropic
C. Adiabatic
D. Isochoric
Answer : A

10. 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

11. 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

12. A centrifugal compressor works on the principle of
A. Conversion of pressure energy into kinetic energy
B. Conversion of kinetic energy into pressure energy
C. Centripetal action
D. Generating pressure directly
Answer : B

13. 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

14. 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

15. A 3 m³/min compressor means that it
A. Compresses 3 m³/min of standard air
B. Compresses 3 m³/ min of free air
C. Delivers 3 m³/ min of compressed air
D. Delivers 3 m³/ min of compressed air at delivery pressure
Answer : B

16. The indicated work per unit mass of air delivered is
A. Directly proportional to clearance volume
B. Greatly affected by clearance volume
C. Not affected by clearance volume
D. Inversely proportional to clearance volume
Answer : C

17. 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

18. 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

19. 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

20. The fuel consumption in gas turbines is accounted for by
A. Lower heating value
B. Higher heating value
C. Heating value
D. Higher calorific value
Answer : A

21. The temperature of air at the beginning of the compression stroke is ________ the atmospheric temperature.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

22. 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

23. In the cross compounding of the gas turbine plant
A. H.P. compressor is connected to H.P. turbine and L.P. compressor to L.P. turbine
B. H.P. compressor is connected to L.P. turbine and L.P. compressor is connected to H.P. turbine
C. Both the arrangements can be employed
D. All are connected in series
Answer : B

24. Pick up the wrong statement
A. Large gas turbines employ axial flow compressors
B. Axial flow compressors are more stable than centrifugal type compressors but not as efficient
C. Axial flow compressors have high capacity and efficiency
D. Axial flow compressors have instability region of operation
Answer : B

25. The air-fuel ratio in gas turbines is of the order of
A. 7 : 1
B. 15 : 1
C. 30 : 1
D. 50 : 1.
Answer : D

26. 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

27. As the turbine inlet temperature increases, the thermal efficiency of gas turbine for the optimum pressure ratio
A. Increases
B. Decreases
C. Remain same
D. First increases and then decreases
Answer : A

28. 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

29. The process, which causes the air to enter the impeller blades of a centrifugal compressor at ________ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.
A. Reduced
B. Increased
C. Zero
D. None of these
Answer : A

30. 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

31. 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

32. 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

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

34. When air is to be compressed at a high pressure, then it is advantageous to use
A. Single stage compression
B. Multistage compression without intercooling
C. Multistage compression with intercooling
D. None of these
Answer : C

35. In a single acting reciprocating air compressor, without clearance, the compression of air may be
A. Isothermal
B. Polytropic
C. Isentropic
D. Any one of these
Answer : D

36. The weight per horse power ratio for gas in Turbine as compared to I.C. engine and steam turbine is
A. Same
B. Higher
C. Lower
D. None of these
Answer : C

37. 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

38. If the flow of air through the compressor is perpendicular to its axis, then it is a
A. Reciprocating compressor
B. Centrifugal compressor
C. Axial flow compressor
D. Turbo compressor
Answer : B

39. The main purpose of reheating in gas turbine is to
A. Increase temperature
B. Reduce turbine size
C. Increase power output
D. Increase speed
Answer : C

40. 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

41. 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

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

43. 1 m of air at atmospheric condition weighs approximately
A. 0.5 kg
B. 1.0 kg
C. 1.3 kg
D. 2.2 kg
Answer : C

44. 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

45. In the axial flow gas turbine, the work ratio is the ratio of
A. Compressor work and turbine work
B. Output and input
C. Actual total head temperature drop to the isentropic total head drop from total head inlet to static head outlet
D. Actual compressor work and theoretical compressor work
Answer : C

46. 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

47. The capacity of a compressor is 5 m /min refers to
A. Standard air
B. Free air
C. Compressed air
D. Compressed air at delivery pressure
Answer : B

48. 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

49. The maximum combustion pressure in gas turbine as compared to I.C. engine is
A. More
B. Less
C. Same
D. Depends on other factors
Answer : B

50. In a turbo jet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded in
A. Exit nozzle, which is a constant volume process
B. Exit nozzle, which is essentially an isentropic process
C. Turbine blades, which is a constant volume process
D. Turbine blades, which is essentially an isentropic process
Answer : D