UPSC IES - Compressors, Gas Turbines & Jet Engines 1000+ MCQ [Solved] PDF Download

1. 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

2. The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is
A. Pressure drop across the valves
B. Superheating in compressor
C. Clearance volume and leakages
D. All of these
Answer : D

3. 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

4. Rotary compressors are suitable for
A. Large discharge at high pressure
B. Low discharge at high pressure
C. Large discharge at low pressure
D. Low discharge at low pressure
Answer : C

5. In a centrifugal compressor, the flow of air is ________ to the axis of compressor.
A. Parallel
B. Perpendicular
C. Inclined
D. None of these
Answer : B

6. 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

7. 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

8. 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

9. For perfect intercooling in a two stage compressor
A. p?/p? = p?/p?
B. p?/p? = p?/p?
C. p? = p?
D. p? = p? p?
Answer : A

10. To avoid moisture troubles, the branch connections from compressed air lines should be taken from
A. Top side of main
B. Bottom side of main
C. Left side of main
D. Right side of main
Answer : A

11. 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

12. 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

13. The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as
A. Compressor efficiency
B. Volumetric efficiency
C. Isothermal efficiency
D. Mechanical efficiency
Answer : B

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

15. 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

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

17. In a centrifugal compressor, an increase in speed at a given pressure ratio causes
A. Increase in flow
B. Decrease in flow
C. Increase in efficiency
D. Increase in flow and decrease in efficiency
Answer : D

18. 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

19. With the decrease in compression ratio, the volumetric efficiency
A. Does not change
B. Increases
C. Decreases
D. First decrease and then increase
Answer : B

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. 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

22. In jet engines, paraffin is usually used as the fuel because of its
A. High calorific value
B. Ease of atomisation
C. Low freezing point
D. Both (A) and (C) above
Answer : D

23. Phenomenon of choking in compressor means
A. No flow of air
B. Fixed mass flow rate regardless of pressure ratio
C. Reducing mass flow rate with increase in pressure ratio
D. Increased inclination of chord with air steam
Answer : B

24. 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

25. The thermal efficiency of a gas turbine as compared to a diesel plant is
A. Same
B. More
C. Less
D. Depends on other factors
Answer : C

26. 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

27. 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

28. 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

29. The volume of air delivered in a medium capacity air compressor per unit time is
A. 0.1 to 1.2 m³/s
B. 0.15 to 5 m³/s
C. Above 5 m³/s
D. None of these
Answer : B

30. 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

31. 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

32. 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

33. The capacity of a compressor is expressed in
A. kg/m²
B. kg/m³
C. m³/min
D. m³/kg
Answer : C

34. In a reciprocating air compressor, the compression work per kg of air
A. Increases as clearance volume increases
B. Decreases as clearance volume increases
C. Is independent of clearance volume
D. Increases as clearance volume decreases
Answer : C

35. 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

36. 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

37. 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

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

39. The ratio of isentropic work to Eulers work is known as
A. Compressor efficiency
B. Isentropic efficiency
C. Euler's efficiency
D. Pressure coefficient
Answer : D

40. Work ratio of a gas turbine may be improved by
A. Decreasing the compression work
B. Increasing the compression work
C. Increasing the turbine work
D. Both (A) and (C) above
Answer : D

41. 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

42. During base load operation, the best method of controlling compressor is
A. Star-stop motor
B. Constant speed unloader
C. Relief valve
D. Variable speed
Answer : A

43. The effective power of gas turbines is increased by adding the following in compressor
A. Ammonia and water vapour
B. Carbon dioxide
C. Nitrogen
D. Hydrogen
Answer : A

44. Atmospheric pressure is 1.03 kg/cm and vapour pressure is 0.03 kg/cm. The air pressure will be
A. 1.03 kg/cm²
B. 1.06 kg/cm²
C. 1.00 kg/cm²
D. 0.53 kg/cm²
Answer : C

45. The ratio of the net work obtained from the gas turbine plant to the turbine work is known as
A. Compression ratio
B. Work ratio
C. Pressure ratio
D. None of these
Answer : B

46. Volumetric efficiency of a compressor without clearance volume
A. Increases with increase in compression ratio
B. Decreases with increase in compression ratio
C. Is not dependent upon compression ratio
D. May increase/decrease depending on compressor capacity
Answer : C

47. 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

48. Water is injected in gas turbine cycle to
A. Control temperature
B. Control output of turbine
C. Control fire hazards
D. Increase efficiency
Answer : B

49. Fighter bombers use following type of engine
A. Turbojet
B. Turbo-propeller
C. Rocket
D. Ramjet
Answer : A

50. 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