Compressors, Gas Turbines & Jet Engines MCQ Solved Paper for RBI Grade B officer

1. 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

2. The thrust on the rotor in a centrifugal compressor is produced by
A. Radial component
B. Axial component
C. Tangential component
D. None of the above
Answer : B

3. 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

4. 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

5. An aftercooler is used to
A. Remove impurities from air
B. Reduce volume of air
C. Cause moisture and oil vapour to drop out
D. Cool the air
Answer : C

6. 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

7. Gas turbine cycle with regenerator
A. Increases thermal efficiency
B. Allows high compression ratio
C. Decreases heat loss is exhaust
D. Allows operation at very high altitudes
Answer : A

8. 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

9. Gas turbine works on
A. Brayton or Atkinson cycle
B. Carnot cycle
C. Rankine cycle
D. Erricson cycle
Answer : A

10. 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

11. The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called
A. Slip factor
B. Velocity factor
C. Velocity coefficient
D. None of the above
Answer : A

12. Free air is the air at
A. Atmospheric conditions at any specific location
B. 20°C and 1 kg/cm² and relative humidity of 36%
C. 0°C and standard atmospheric conditions
D. 15°C and 1 kg/cm²
Answer : A

13. The closed cycle in gas turbines
A. Provides greater flexibility
B. Provides lesser flexibility
C. In never used
D. Is used when gas is to be burnt
Answer : A

14. Adiabatic compression is one in which
A. Temperature during compression remains constant
B. No heat leaves or enters the compressor cylinder during compression
C. Temperature rise follows a linear relationship
D. Work done is maximum
Answer : B

15. Volumetric efficiency is
A. The ratio of stroke volume to clearance volume
B. The ratio of the air actually delivered to the amount of piston displacement
C. Reciprocal of compression ratio
D. Index of compressor performance
Answer : B

16. 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

17. A large clearance volume in a reciprocating compressor results in
A. Reduced volume flow rate
B. Increased volume flow rate
C. Lower suction pressure
D. Lower delivery pressure
Answer : A

18. Pick up the wrong statement
A. Pulsejet requires no ambient air for propulsion
B. Ramjet engine has no turbine
C. Turbine drives compressor in a Turbojet
D. Bypass turbojet engine increases the thrust without adversely affecting, the propulsive efficiency and fuel economy
Answer : A

19. Rotary compressor is best suited for
A. Large quantity of air at high pressure
B. Small quantity of air at high pressure
C. Small quantity of air at low pressure
D. Large quantity of air at low pressure
Answer : B

20. In a jet engine, the air-fuel ratio is
A. 30 : 1
B. 40 : 1
C. 50 : 1
D. 60 : 1
Answer : D

21. In a single stage, single acting reciprocating air compressor, without clearance, the workdone on the air during isentropic compression is ________ the heat required to raise the temperature of air from T? to T? at a constant pressure.
A. Equal to
B. Less than
C. Greater than
D. None of these
Answer : A

22. 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

23. 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

24. 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

25. When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is ________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : A

26. Which of the following statement is correct relating to rocket engines?
A. The combustion chamber in a rocket engine is directly analogous to the reservoir of a supersonic wind tunnel
B. The stagnation conditions exist at the combustion chamber
C. The exit velocities of exhaust gases are much higher than those in jet engine
D. All of the above
Answer : D

27. Out of the following, from where you will prefer to take intake for air compressor
A. From an air conditioned room maintained at 20°C
B. From outside atmosphere at 1°C
C. From coal yard side
D. From a side where cooling tower is located nearby
Answer : D

28. The overall isothermal efficiency of the compressor is defined as the ratio of
A. Work required to compress the air isothermally to the actual work required to compress the air for the same pressure ratio
B. Isothermal power to the shaft power or B.P. of the motor or engine required to drive the compressor
C. Volume of free air delivery per stroke to the swept volume of the piston
D. Isentropic power to the power required to drive the compressor
Answer : B

29. For an irreversible gas turbine cycle, the efficiency and work ratio both depend on
A. Pressure ratio alone
B. Maximum cycle temperature alone
C. Minimum cycle temperature alone
D. Both pressure ratio and maximum cycle temperature
Answer : D

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. 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

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

33. The capacity of compressor will be highest when its intake temperature is
A. Lowest
B. Highest
C. Anything
D. Atmospheric
Answer : D

34. Separators in compressor installations are located
A. Before intercooler
B. After intercooler
C. After receiver
D. Between after-cooler and air receiver
Answer : D

35. 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

36. 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

37. The compression ratio in a gas turbine is of the order of
A. 3.5 : 1
B. 5 : 1
C. 8 : 1
D. 12 : 1
Answer : C

38. 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

39. The ratio of isentropic work to Euler work is known as
A. Pressure coefficient
B. Work coefficient
C. Polytropic reaction
D. Slip factor
Answer : A

40. Maximum delivery pressure is a rotary air compressor is of the order of
A. 6 kg/cm²
B. 10 kg/cm²
C. 16 kg/cm²
D. 25 kg/cm²
Answer : B

41. The propulsive power of the rocket is (where v? = Jet velocity, and v? = Aircraft velocity)
A. (v?² -v?²)/2g
B. (v? - v?)²/2g
C. (v?² -v?²)/g
D. (v? - v?)²/g
Answer : A

42. Which is false statement about multistage compression?
A. Power consumption per unit of air delivered is low
B. Volumetric efficiency is high
C. It is best suited for compression ratios around 7:1
D. The moisture in air is condensed in the intercooler
Answer : B

43. 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

44. Euler's equation can be used for
A. Radial flow compressors
B. Axial flow compressors
C. Pumps
D. All of these
Answer : D

45. 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

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

49. 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

50. 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