Compressors, Gas Turbines & Jet Engines MCQ Solved Paper for SSC Scientific Assistant

1. In gas turbines, high thermal efficiency is obtained in
A. Closed cycle
B. Open cycle
C. Both of the above
D. Closed/open depending on other considerations
Answer : A

2. 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

3. 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

4. The thrust of a jet propulsion power unit can be increased by
A. Injecting water into the compressor
B. Burning fuel after gas turbine
C. Injecting ammonia into the combustion chamber
D. All of the above
Answer : D

5. Which is false statement about air receivers?
A. These are used to dampen pulsations
B. These act as reservoir to take care of sudden demands
C. These increase compressor efficiency
D. These knock out some oil and moisture
Answer : C

6. 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

7. 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

8. 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

9. 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

10. 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

11. Isothermal compression efficiency can be attained by running the compressor
A. At very high speed
B. At very slow speed
C. At average speed
D. At zero speed
Answer : B

12. 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

13. In which case the air-fuel ratio is likely to be maximum?
A. Gas turbine
B. 4-stroke petrol engine
C. 4-stroke diesel engine
D. Multi cylinder engine
Answer : A

14. 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

15. The compressor capacity is defined as 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 : B

16. The following property is most important for material used for gas turbine blade
A. Toughness
B. Fatigue
C. Creep
D. Corrosion resistance
Answer : C

17. The overall efficiency of the compressed air system is the
A. Ratio of shaft output of the air motor to the shaft input to the compressor
B. Ratio of shaft input to the compressor to the shaft output of air motor
C. Product of shaft output of air motor and shaft input to the compressor
D. None of the above
Answer : A

18. 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

19. The net work input required for compressor with increase in clearance volume
A. Increases
B. Decreases
C. Remains same
D. Increases/decreases depending on compressor capacity
Answer : C

20. The clearance volume of the air compressor is kept minimum because
A. It allows maximum compression to be achieved
B. It greatly affects volumetric efficiency
C. It results in minimum work
D. It permits isothermal compression
Answer : B

21. 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

22. For slow speed large capacity compressor, following type of valve will be best suited
A. Poppet valve
B. Mechanical valve of the Corliss, sleeve, rotary or semi rotary type
C. Disc or feather type
D. Any of the above
Answer : C

23. 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

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

25. The pressure ratio in gas turbines is of the order of
A. 2 : 1
B. 4 :1
C. 61 : 1
D. 9 : 1
Answer : C

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. A compressor at high altitudes will require ________ power.
A. Same
B. Less
C. More
D. None of these
Answer : B

34. Reheating in a multistage expansion gas turbine __________ compressor work.
A. Has no effect on
B. Decreases
C. Increases
D. None of these
Answer : B

35. The volumetric efficiency of a compressor falls roughly as follows for every 5°C increase in atmospheric temperature
A. 0.1 %
B. 0.5 %
C. 1 %
D. 5 %
Answer : C

36. 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

37. The velocity of air entering in a rocket is ________ as compared to an aircraft.
A. Zero
B. Less
C. More
D. Same
Answer : A

38. The ratio of specific weight/h.p. of gas turbine and I.C engines may be typically of the order of
A. 1 : 1
B. 2 : 1
C. 4 : 1
D. 1 : 6
Answer : D

39. 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

40. After-cooler is used to
A. Cool the air
B. Decrease the delivery temperature for ease in handling
C. Cause moisture and oil vapour to drop out
D. Reduce volume
Answer : C

41. Maximum temperature in a gas turbine is of the order of
A. 700°C
B. 2000°C
C. 1500°C
D. 1000°C
Answer : A

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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

48. The workdone on a compressor will be minimum if air is taken from
A. The atmosphere
B. A source at 0°C
C. A source of low temperature air
D. A source of high temperature air
Answer : C

49. Aeroplanes employ following type of compressor
A. Radial flow
B. Axial flow
C. Centrifugal
D. None of the above
Answer : B

50. 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