Compressors, Gas Turbines & Jet Engines MCQ Solved Paper for CAT

1. Propulsion efficiency of the following order is obtained in practice
A. 34 %
B. 50 %
C. 60 %
D. 72 %
Answer : C

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

3. The compressed air may be used
A. In gas turbine plants
B. For operating pneumatic drills
C. In starting and supercharging of I.C. engines
D. All of the above
Answer : D

4. The output of a gas turbine is 300 KW and its efficiency is 20 percent, the heat supplied is
A. 6000 KW
B. 15 KW
C. 600 KW
D. 150 KW
Answer : B

5. 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

6. 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

7. What will be the volume of air at 327°C if its volume at 27°C is 1.5 m³/ mt?
A. 3 m³/ mt.
B. 1.5 m³/ mt.
C. 18 m³/ mt.
D. 6 m³/ mt.
Answer : A

8. 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

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

10. The pressure and temperature conditions of air at the suction of compressor are
A. Atmospheric
B. Slightly more than atmospheric
C. Slightly less than atmospheric
D. Pressure slightly less than atmospheric and temperature slightly more than atmospheric
Answer : D

11. The ratio of the increase in pressure in rotor blades to total increase in pressure in the stage is called
A. Pressure ratio
B. Pressure coefficient
C. Degree of reaction
D. Slip factor
Answer : C

12. 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

13. 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

14. 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

15. 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

16. In a jet propulsion
A. The propulsive matter is ejected from within the propelled body
B. The propulsive matter is caused to flow around the propelled body
C. Its functioning does not depend upon presence of air
D. None of the above
Answer : B

17. The mass of gas turbine per kW developed is about ________ as that of an I.C. engine.
A. Same
B. One-half
C. One fourth
D. One sixth
Answer : D

18. 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

19. 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

20. Which of the following plants is smallest and lightest for generating a given amount of power?
A. Gas turbine plant
B. Petrol engine
C. Diesel engine
D. Solar plant
Answer : A

21. 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

22. 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

23. 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

24. 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

25. The specific output per kg mass flow rate of a gas turbine (having fixed efficiencies of compressor and turbine and fixed higher and lower temperature) with increase in pressure ratio will
A. Increase first at fast rate and then slow
B. Increase first at slow rate and then fast
C. Decrease continuously
D. First increase, reach maximum and then decrease
Answer : D

26. The gas in cooling chamber of a closed cycle gas turbine is cooled at
A. Constant volume
B. Constant temperature
C. Constant pressure
D. None of these
Answer : C

27. 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

28. 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

29. 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

30. The ratio of the indicated power to the shaft power or brake power of the motor or engine required to drive the compressor, is called
A. Compressor efficiency
B. Volumetric efficiency
C. Isothermal efficiency
D. Mechanical efficiency
Answer : D

31. 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

32. Pick up the correct statement
A. Gas turbine uses low air-fuel ratio to economise on fuel
B. Gas turbine uses high air-fuel ratio to reduce outgoing temperature
C. Gas turbine uses low air-fuel ratio to develop the high thrust required
D. All of the above
Answer : B

33. 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

34. 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

35. 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

36. Gas turbine blades are given a rake
A. Equal to zero
B. In the direction of motion of blades
C. Opposite to the direction of motion of blades
D. Depending on the velocity
Answer : B

37. Ramjet engine
A. Is self operating at zero flight speed
B. Is not self operating at zero flight speed
C. Requires no air for its operation
D. Produces a jet consisting of plasma
Answer : B

38. 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

39. 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

40. 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

41. Pick up wrong statement. Surging phenomenon in centrifugal compressor depends on
A. Mass flow rate
B. Pressure ratio
C. Change in load
D. Stagnation pressure at the outlet
Answer : D

42. 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

43. 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

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. Rotary compressors are used for delivering
A. Small quantities of air at high pressures
B. Large quantities of air at high pressures
C. Small quantities of air at low pressures
D. Large quantities of air at low pressures
Answer : D

46. 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

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

49. The efficiency of the vane blower is (where W? = Workdone due to compression, and W? = Workdone due to back flow)
A. W?/(W? + W?)
B. W?/(W? + W?)
C. (W? + W?)/W?
D. (W? + W?)/W?
Answer : B

50. Compression efficiency is compared against
A. Ideal compression
B. Adiabatic compression
C. Isentropic compression
D. Isothermal compression
Answer : D