asportzone.com – MCQs, Mock Tests | Engineering Compressors, Gas Turbines and Jet Engines MCQ Practice Test

1 In jet propulsion power unit, the inlet duct of diverging shape is used in order to

A Collect more air B Convert kinetic energy of air into pressure energy C Provide robust structure D Beautify the shape

✅ Correct Answer: 2

2 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

✅ Correct Answer: 3

3 The mean effective pressure of the compressor is the

A ctual 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

✅ Correct Answer: 4

4 An ideal air compressor cycle without clearance on P-V 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

✅ Correct Answer: 1

5 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

✅ Correct Answer: 4

6 Maximum work is done in compressing air when the compression is

A Isothermal B Adiabatic C Polytropic D None of these

✅ Correct Answer: 2

7 A rotary compressor is driven by an

A Electric motor B Engine C Either (A) or (B) D None of these

✅ Correct Answer: 3

8 Isothermal compression though most efficient, but is not practicable because

A It requires very big cylinder B It does not increase pressure much C It is impossible in practice D Compressor has to run at very slow speed to achieve it

✅ Correct Answer: 4

9 Gas turbine as compared to steam turbine

A equires less space for installation B Has compressor and combustion chamber C Has less efficiency D All of the these

✅ Correct Answer: 4

10 The following property is most important for material used for gas turbine blade

A Toughness B Fatigue C Creep D Corrosion resistance

✅ Correct Answer: 3

11 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

✅ Correct Answer: 4

12 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

✅ Correct Answer: 4

13 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

✅ Correct Answer: 2

14 Compression efficiency is compared against

A Ideal compression B Adiabatic compression C Isentropic compression D Isothermal compression

✅ Correct Answer: 4

15 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

✅ Correct Answer: 3

16 An ideal air compressor cycle with clearance on P-V 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

✅ Correct Answer: 2

17 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

✅ Correct Answer: 1

18 Ratio of indicated H.P. and brake H.P. is known as

A Mechanical efficiency B Volumetric efficiency C Isothermal efficiency D Adiabatic efficiency

✅ Correct Answer: 1

19 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

✅ Correct Answer: 2

20 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

✅ Correct Answer: 4

21 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

✅ Correct Answer: 4

22 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

✅ Correct Answer: 3

23 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 these

✅ Correct Answer: 1

24 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

✅ Correct Answer: 2

25 A machine used to raise the pressure of air is called

A Gas turbine B C engine C Compressor D Air motor

✅ Correct Answer: 3

26 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

✅ Correct Answer: 2

27 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

✅ Correct Answer: 1

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

✅ Correct Answer: 1

29 In a centrifugal compressor, the ratio of the ________ to the blade velocity is called slip factor.

A Inlet whirl velocity B Outlet whirl velocity C Inlet velocity of flow D Outlet velocity of flow

✅ Correct Answer: 4

30 The most efficient method of compressing air is to compress it

A Isothermally B Adiabatically C Isentropically D Isochronically

✅ Correct Answer: 1

31 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

✅ Correct Answer: 2

32 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

✅ Correct Answer: 4

33 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

✅ Correct Answer: 2

34 Isothermal compression efficiency can be attained by running the compressor

A (A) At very high speed B At very slow speed C At average speed D At zero speed

✅ Correct Answer: 2

35 . 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

✅ Correct Answer: 4

36 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

✅ Correct Answer: 4

37 More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than

A 2 kg/cmÂ² B 6 kg/cmÂ² C 10 kg/cmÂ² D 14.7 kg/cmÂ²

✅ Correct Answer: 1

38 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

✅ Correct Answer: 4

39 The advantage of multistage compression over single stage compression is

A Lower power consumption per unit of air delivered B Higher volumetric efficiency C Decreased discharge temperature D All of the above

✅ Correct Answer: 4

40 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

✅ Correct Answer: 4

41 More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than

A 2 kg/cmÂ² B 6 kg/cmÂ² C 10 kg/cmÂ² D 14.7 kg/cmÂ²

✅ Correct Answer: 1

42 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

✅ Correct Answer: 4

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

✅ Correct Answer: 4

44 The advantage of multistage compression over single stage compression is

A Lower power consumption per unit of air delivered B Higher volumetric efficiency C Decreased discharge temperature D All of the above

✅ Correct Answer: 4

45 Reheating in a gas turbine

A Increases the thermal efficiency B Increases the compressor work C Increases the turbine work D Decreases the thermal efficiency

✅ Correct Answer: 1

46 Pick up the wrong statement about advantages of multistage compression

A Better lubrication is possible advantages of multistage (B) (D) B More loss of air due to leakage past the cylinder C Mechanical balance is better D Air can be cooled perfectly in between

✅ Correct Answer: 2

47 For perfect intercooling in a three stage compressor

A pâ‚‚/pâ‚ = pâ‚ƒ/pâ‚‚ = pâ‚„/pâ‚ƒ B pâ‚ƒ/pâ‚ = pâ‚„/pâ‚‚ C pâ‚ pâ‚‚ = pâ‚ƒ pâ‚„ D pâ‚ pâ‚ƒ = pâ‚‚ pâ‚„

✅ Correct Answer: 1

48 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

✅ Correct Answer: 1

49 When the temperature of air leaving the inter-cooler, in a two stage compression with inter-cooler, 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

✅ Correct Answer: 1

50 Losses in a centrifugal compressor are due to

A Inlet losses B Impeller channel losses C Diffuser losses D All of the above

✅ Correct Answer: 4

51 he axial flow compressor is preferred in aircraft gas turbines because of

A Low frontal area B Higher thrust C High pressure rise D None of these

✅ Correct Answer: 1

52 The volumetric efficiency of a compressor falls roughly as follows for every 5Â°C increase in atmospheric temperature

A 0.1% B 0.5% C 1% D 5%

✅ Correct Answer: 2

53 If pâ‚, is the pressure of air entering the L.P. cylinder and pâ‚‚ is the pressure of air leaving the L.P. cylinder (or inter-cooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where Dâ‚ = Dia. of L.P. cylinder, and Dâ‚‚ = Dia. of H.P. cylinder)

A Dâ‚/Dâ‚‚ = pâ‚ pâ‚‚ B Dâ‚/Dâ‚‚ = pâ‚/pâ‚‚ C Dâ‚/Dâ‚‚ = pâ‚‚/pâ‚ D None of these

✅ Correct Answer: 3

54 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

✅ Correct Answer: 3

55 Which of the following statement is correct?

A The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency B The compression ratio for the compressor is always greater than unity C The compressor capacity is the ratio of work-done per cycle to the stroke volume D During isothermal compression of air, the work-done in a compressor is maximum

✅ Correct Answer: 2

56 n nâ‚ and nâ‚‚ are the indices of compression for the first and second stage of compression, then the ratio of work-done on the first and second stages (Wâ‚/Wâ‚‚) with perfect intercooling is given by

A Wâ‚/Wâ‚‚ = nâ‚‚(nâ‚ - 1)/nâ‚(nâ‚‚ - 1) B Wâ‚/Wâ‚‚ = nâ‚(nâ‚‚ - 1)/nâ‚‚(nâ‚ - 1) C Wâ‚/Wâ‚‚ = nâ‚/nâ‚‚ D Wâ‚/Wâ‚‚ = nâ‚‚/nâ‚

✅ Correct Answer: 2

57 For supplying intermittent small quantity of air at high pressure, following compressor is best suited

A Centrifugal B Reciprocating C Axial D Screw

✅ Correct Answer: 2

58 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

✅ Correct Answer: 3

59 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

✅ Correct Answer: 4

60 The volume of air delivered in a medium capacity air compressor per unit time is

A 0.1 to 1.2 mÂ³/s B 0.15 to 5 mÂ³/s C Above 5 mÂ³/s D None of these

✅ Correct Answer: 2

61 For a two stage compressor, if index of compression for higher stage is greater than index of compression for lower stage, then the optimum pressure as compared to ideal case will

A Increase B Decrease C Remain unaffected D Other factors control it

✅ Correct Answer: 1

62 Which one of the following is the effect of blade shape on performance of a centrifugal compressor?

A Backward curved blades has poor efficiency B Backward curved blades lead to stable performance C Forward curved blades has higher efficiency D Forward curved blades produce lower pressure ratio

✅ Correct Answer: 4

63 Diffuser in a compressor is used to

A Increase velocity B Make the flow streamline C Convert pressure energy into kinetic energy D Convert kinetic energy into pressure energy

✅ Correct Answer: 4

64 A closed cycle gas turbine consists of a

A Compressor B Heating chamber C Cooling chamber D All of these

✅ Correct Answer: 4

65 The ratio of isentropic work to Eulerâ€™s work is known as

A Compressor efficiency B Isentropic efficiency C Euler's efficiency D Pressure coefficient

✅ Correct Answer: 4

66 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

✅ Correct Answer: 4

67 The thermodynamic efficiency of rotary compressor is based on

A Isothermal compression B Adiabatic compression C Isentropic compression D Polytropic compression

✅ Correct Answer: 2

68 The type of rotary compressor used in aeroplanes, is of

A Centrifugal type B Axial flow type C Radial flow type D None of these

✅ Correct Answer: 2

69 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

✅ Correct Answer: 2

70 The assumption made in two stage compression with inter-cooler is that

A There is no pressure drop in the inter-cooler 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

✅ Correct Answer: 4

71 Propulsive efficiency is defined as ratio of

A Thrust power and fuel energy B Engine output and propulsive power C Propulsive power and fuel input D Thrust power and propulsive power

✅ Correct Answer: 4

72 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

✅ Correct Answer: 4

73 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

✅ Correct Answer: 1

74 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

✅ Correct Answer: 3

75 Propulsion efficiency of the following order is obtained in practice

A 34% B 50% C 60% D 72%

✅ Correct Answer: 3

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Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 02