Compressors, Gas Turbines & Jet Engines 1000+ MCQ with answer for SSC Stenographer

1. 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

2. 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

3. 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

4. Surging 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 : C

5. 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

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

7. 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

8. 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

9. 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

10. Pick up the false statement
A. Gas turbine is a self starting unit
B. Gas turbine does not require huge quantity of water like steam plant
C. Exhaust losses in gas turbine are high due to large mass flow rate
D. Overall efficiency of gas turbine plant is lower than that of a reciprocating engine
Answer : A

11. An air compressor may be controlled by
A. Throttle control
B. Clearance control
C. Blow off control
D. Any one of the above
Answer : D

12. 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

13. Axial flow compressor has the following advantage over centrifugal compressor
A. Larger air handling ability per unit frontal area
B. Higher pressure ratio per stage
C. Aerofoil blades are used
D. Higher average velocities
Answer : A

14. In open cycle turbojet engines used in military aircraft, reheating the exhaust gas from the turbine by burning, more fuel is used to increase the
A. Thrust and range of aircraft
B. Efficiency of the engine
C. Both (A) and (B)
D. None of these
Answer : A

15. 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

16. An ideal air compressor cycle without 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 : A

17. 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

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

19. A jet engine works on the principle of conservation of
A. Mass
B. Energy
C. Flow
D. Linear momentum
Answer : D

20. The thermal efficiency of a simple gas turbine for a given turbine inlet temperature with increase in pressure ratio
A. Increases
B. Decreases
C. First increases and then decreases
D. First decreases and then increases
Answer : A

21. 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

22. The working fluid in a turbine is
A. In two phases
B. In three phases
C. In a single phase
D. In the form of air and water mixture
Answer : C

23. Pick up the wrong statement
A. Centrifugal compressors deliver practically constant pressure over a considerable range of capacities
B. Axial flow compressors have a substantially constant delivery at variable pressures
C. Centrifugal compressors have a wider stable operating range than axial flow compressors
D. Axial flow compressors are bigger in diameter compared to centrifugal type
Answer : D

24. 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

25. The efficiency of jet engine is
A. Lower at low speed
B. Higher at high altitudes
C. Same at all altitudes
D. Higher at high speed
Answer : B

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

27. 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

28. 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

29. The compressor performance at higher altitude compared to sea level will be
A. Same
B. Higher
C. Lower
D. Dependent on other factors
Answer : C

30. 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

31. 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

32. Ratio of indicated H.P. and brake H.P. is known as
A. Mechanical efficiency
B. Volumetric efficiency
C. Isothermal efficiency
D. Adiabatic efficiency
Answer : A

33. 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

34. 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

35. 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

36. The absolute pressure of air at the outlet of a compressor is called
A. Back pressure
B. Critical pressure
C. Discharge pressure
D. None of these
Answer : C

37. 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

38. 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

39. The pressure ratio for an open cycle gas turbine compared to closed cycle gas turbine of same h.p. is
A. Low
B. High
C. Same
D. Low/high depending on make and type
Answer : A

40. 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

41. A compressor mostly used for supercharging of I.C. engines is
A. Radial flow compressor
B. Axial flow compressor
C. Roots blower
D. Reciprocating compressor
Answer : A

42. 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

43. The compression ratio for the compressor is always __________ unity.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C

44. The area of actual indicator diagram on an air compressor as compared to area of ideal indicator diagram is
A. Less
B. More
C. Same
D. More/less depending on compressor capacity
Answer : B

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

46. 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

47. 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

48. 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

49. 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

50. 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