Quiz  /  Compressors Gas Turbines and Jet Engines MCQ Interview Questions and Answers

  • 1. 
    Free air is the air at

  • atmospheric conditions at any specific location
  • 20°C and 1 kg/cm2 and relative humidity of 36%
  • 0°C and standard atmospheric conditions
  • 15°C and 1 kg/cm2
  • 25°C, 1 kg/cm2 and relative humidity of 50%.

  • 2. 
    Standard air is the air at

  • atmospheric conditions at any specific location
  • 20°C and 1 kg/cm2 and relative humidity 36%
  • 0°C and standard atmospheric conditions
  • 15°C and 1 kg/cm2
  • 25°C, 1 kg/cm2 and RH of 60%.

  • 3. 
    1 m of air at atmospheric condition weighs approximately

  • 0.5 kg
  • 1.0 kg
  • 1.3 kg
  • 2.2 kg
  • 3.2 kg.

  • 4. 
    Adiabatic compression is one in which

  • temperature during compression remains constant
  • no heat leaves or enters the compressor cylinder during cornpression
  • temperature rise follows a linear relationship
  • work done is maximum
  • entropy decreases.

  • 5. 
    The capacity of a compressor is 5 m /mih. 5 m /min refers to

  • standard air
  • free air
  • compressed air
  • compressed air at delivery pressure
  • air sucked.

  • 6. 
    The overall isothermal eiffciency of compressor is defined as the ratio of

  • isothermal h.p. to the BHP of motor
  • isothermal h.p. to adiabatic h.p.
  • power to drive compressor to isothermal h.p.
  • work to compress air isothermally to work for actual compression
  • isothermal work to ideal work.

  • 7. 
    The- most efficient method of compressing air is to compress it

  • isothermally
  • adiabatically
  • isentropically
  • isochronically
  • as per law pV

  • 8. 
    Maximum work is done in compressing air when the compression is

  • isothermal
  • adiabatic
  • polytropic
  • any one of the above
  • none of the above.

  • 9. 
    The pressure and temperature conditions of air at the suction of compressor are

  • atmospheric
  • slightly more than atmospheric
  • slightly less than atmospheric
  • pressure slightly more than atmospheric and temperature slightly less than atmospheric
  • pressure sightly less than atmospheric and temperature slightly more than atmospheric.

  • 10. 
    Isothermal compression effeicency can be attained by running the compressor

  • at very high speed
  • at very slow speed
  • at average speed
  • at zero speed
  • isothermally.

  • 11. 
    The compressor capacity with decrease in suction temperature

  • increases
  • decreases
  • remains unaffected
  • may increase or decrease depending on compressor capacity
  • increases upto certain limit and then decreases.

  • 12. 
    Isothermal compression efficiency, even when running at high speed, can be approached by using

  • multi-stage compression
  • cold water spray
  • both (a) and (b) above
  • fully insulating the cylinder
  • high stroke.

  • 13. 
    Compression efficiency is compared against

  • ideal compression
  • adiabatic compression
  • botii isothermal and adiabatic compression
  • isentropic compression
  • isothermal compression.

  • 14. 
    Aeroplanes employ following type of compressor

  • radial flow
  • axial flow
  • centrifugal
  • combination of above
  • none of the above.

  • 15. 
    Inter cooling in compressors

  • cools the delivered air
  • results in saving of power in compressing a given volume to given pressure
  • is the standard practice for big compressors
  • enables compression in two stages
  • prevents compressor jacket running very hot.

  • 16. 
    An ideal air compressor cycle without clearance on p-v diagram can be represented by following processes

  • one adiabatic, two isobaric, and one constant volume
  • two adiabatic and two isobaric
  • two adiabatic, one isobaric and one constant volume
  • one adiabatic, one isobaric and two constant volume
  • two isobaric, two adiabatic and one constant volume.

  • 17. 
    An ideal air compressor cycle with clearance on p-v diagram can be represented by following processes

  • one adiabatic, two isobaric, and one constant volume
  • two adiabatic and two isobaric
  • two adiabatic, one isobaric and one constant volume,
  • one adiabatic, one isobaric and two constant volume
  • two isobaric, two adiabatic and one constant volume.

  • 18. 
    What will be the volume of air at 327°C if its volume at 27°C is 1.5 m3/mt

  • 3 m3/mt .
  • 1.5 m3/mt
  • 18 m3/mt’
  • 6 m3/mt
  • 0.75 m3/mt.

  • 19. 
    The work done per unit mass of air in compression will’be least when n is equal to

  • 1
  • 1.2 ,
  • 1.3
  • 1.4
  • 1.5

  • 20. 
    Isothermal compression though most efficient, but is not -practicable because

  • ityrequires very big cylinder
  • it does not increase pressure much
  • it is impossible in practice
  • compressor has to run at very slow speed to achieve it
  • it requires cylinder to be placed in water.

  • 21. 
    Ratio of indicated H.P. and brake H.P. is known as

  • mechanical efficiency
  • volumetric efficiency
  • isothermal efficiency
  • adiabatic efficiency
  • relative efficiency.

  • 22. 
    The ratio of work doen per cycle to the swept volume in case of compressor is called

  • compression index
  • compression ratio
  • compressor efficiency
  • mean effective pressure
  • compressor effectiveness.

  • 23. 
    Cylinder clearance in a compressor should be

  • as large as possible
  • as small as possible
  • about 50% of swept volume
  • about 100% of swept volume
  • none of the above.

  • 24. 
    Ratio of compression is the ratio of

  • gauge discharge pressure to the gauge intake pressure
  • absolute discharge pressure to the ab-solute intake pressure
  • pressures at discharge and suction cor-responding to same temperature
  • stroke volume and clearance volume
  • none of the above.

  • 25. 
    Clearance volume in actual reciprocating compressors is essential

  • to accommedate Valves in the cylinder head
  • to provide cushioning effect
  • to attain high volumetric efficiency
  • to avoid mechanical bang of piston with cylinder head
  • to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head.

  • 26. 
    The net work input required for compressor with increase in clearance volume

  • increases
  • decreases
  • remains same
  • increases/decreases depending on com-pressor capacity
  • unpredictable.

  • 27. 
    Ratio of indicated h.p. to shaft h.p. in known as

  • compressor efficiency
  • isothermal efficiency
  • volumetric efficiency
  • mechanical efficiency
  • adiabatic efficiency.

  • 28. 
    Volumetric efficiency is

  • the ratio of stroke volume to clearance volume
  • the ratio of the air actually delivered to the amount of piston displacement
  • reciprocal of compression ratio
  • index of compressor performance
  • proportional to compression ratio.

  • 29. 
    Volumetric efficiency of air compressors is of the order of

  • 20-30%
  • 40-50%
  • 60-70%
  • 70-90%
  • 90-100%.

  • 30. 
    Volumetric efficiency of a compressor with clearance volume

  • increases with increase in compression ratio
  • decreases with increase in compression ratio
  • in not dependent upon compression ratio
  • may increase/decrease depending on compressor capacity
  • unpredictable.

  • 31. 
    Volumetric efficiency of a compressor without clearance volume

  • increases with increase in compression ratio
  • decreases with increase in compression ratio
  • is not dependent upon compressin ratio
  • may increase/decrease depending on compressor capacity
  • unpredictable.

  • 32. 
    The clearance volume of the air compressor is kept minimum because

  • it allows maximum compression to be achieved
  • it greatly affects volumetric efficiency
  • it results in minimum work
  • it permits isothermal compression
  • none of the above.

  • 33. 
    Euler’s equation is applicable for

  • centrifugal compressor
  • axial compressor
  • pumps
  • all of the above
  • none of the above.

  • 34. 
    Out of the following, from where you will prefer to take intake for air compressor

  • from an air conditioned room maintained at 20°C
  • from outside atmosphere at 1°C
  • from coal yard side
  • from a side where cooling tower is located nearby
  • from any one of the above locations.

  • 35. 
    Mining industry usually employs following motive power

  • A.C. electric motor
  • compressed air
  • petrol engine
  • diesel engine
  • D.C. electric motor.

  • 36. 
    Which is false statement about air receivers

  • These are used to dampen pulsations ,
  • These act as reservoir to- take care of sudden demands
  • These increase compressor efficiency
  • These knock out some oil and moisture
  • These reduce frequent on/off operation of compressors.

  • 37. 
    Which is false statement about multistage compression .

  • Power consumption per unit of air delivered is low
  • Volumetric efficiency is high
  • It is best suited for compression ratios around 7:1
  • The moisture in air is condensed in the intercooler
  • Outlet temperature is reduced.

  • 38. 
    In multistage compressor, the isothermal compression is achieved by

  • employing intercooler
  • by constantly cooling the cylinder
  • by running compressor at very slow speed
  • by insulating the cylinder
  • none of the above.

  • 39. 
    Reciprocating air compressor is best suited for

  • large quantity of air at high pressure
  • small quantity of air at high pressure
  • small quantity of air at low pressure
  • large quantity of air at low pressure
  • any one of the above.

  • 40. 
    Rotary compressor is best suited for

  • large quantity of air at high pressure
  • small quantity of air at high pressure
  • small quantity of air at low pressure
  • large quantity of air at low pressure
  • any one of the above.

  • 41. 
    The capacity of compressor will be highest when its intake temperature is

  • lowest
  • highest
  • anything.
  • atmospheric
  • none of the above.

  • 42. 
    After-cooler is used to

  • cool the air
  • decrease the delivery temperature for ease in handling
  • cause moisture and oil vapour to drop out
  • reduce volume
  • increase pressure.

  • 43. 
    To aviod moisture troubles, the compressed air main line should

  • rise gradually towards the point of use
  • drop gradually towards the point of use
  • be laid vertically
  • be laid exactly horizontally
  • none of the above

  • 44. 
    Separators in compressor installations are located

  • before intercooler
  • after intercooler
  • after receiver
  • between after-cooler and air receiver
  • before suction.

  • 45. 
    The area of actual indicator diagram on an air compressor as compared to area of ideal indicator diagram is

  • less
  • more
  • same
  • more/less depending on compressor capacity
  • unpredictable.

  • 46. 
    An air compressor may be controlled by

  • throttle control (b) clearance control
  • blow-off control
  • any one of the above
  • none of the above.

  • 47. 
    The compressor efficiecny is the

  • isothermal H.P/indicated H.R
  • isothermal H.P./shaft H.R
  • total output/air input
  • compression work/motor input
  • none Of the above.

  • 48. 
    To avoid moisture troubles, the branch connections from compressed air lines should be taken from

  • top side of main
  • bottom side of main
  • left side of main
  • right side of main
  • any location.

  • 49. 
    The thrust on the rotor in a centrifugal compressor is produced by

  • radial component
  • axial component
  • tangential component
  • resultant component

  • 50. 
    The compressor performance at higher altitude compared to sea level will be

  • same
  • higher
  • lower
  • dependent on other factors
  • none of the above.

  • 51. 
    A compressor at high altitude will draw

  • more power
  • less power
  • same power
  • more/less power depending on other factors
  • none of the above.

  • 52. 
    During peak load periods, the best method of controlling compressors is

  • start-stop motor
  • constant speed unloader
  • relief valve
  • variable speed
  • none of the above.

  • 53. 
    A centrifugal compressor works on the principle of

  • conversion of pressure energy into kinetic energy
  • conversion of kinetic energy into pres¬sure energy
  • centripetal action
  • generating pressure directly
  • combination of (a) and (d).

  • 54. 
    For a compressor, least work will be done if the compression is

  • isentropic
  • isothermal
  • polytropic
  • somewhere in between isentropic and isothermal
  • none of the above.

  • 55. 
    In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to

  • N.T.P. conditions
  • intake temperature and pressure conditions
  • 0°C and 1 kg/cm2
  • 20°C and 1 kg/cm2
  • none of the above.

  • 56. 
    The volumetirc efficiency of a compressor is calculated on the basis of

  • volume of air inhaled at working conditions
  • volume of air inhaled at N.T.P. conditions
  • volume at 0°C and 1 kg/cm2
  • volume at 20°C and 1 kg/cm2
  • none of the above.

  • 57. 
    The volumetric efficiency of a compressor falls roughly as follows for every 100 m increase in elevation

  • 0.1%
  • 0.5%
  • 1.0%
  • 5%
  • 10%.

  • 58. 
    For slow-speed large capacity compressor, following type of valve will be best suited

  • poppet valve
  • mechanical valve of the corliss, sleeve, rotary or semirotary type
  • disc or feather type
  • any of the above
  • none of the above.

  • 59. 
    During base load operation, the best method of controlling compressor is

  • start-stop motor
  • constant speed unloader
  • relief valve
  • variable speed
  • none of the above.

  • 60. 
    More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than

  • 2 kg/cm2
  • 6 kg/cm2
  • 10 kg/cm2
  • 14.7 kg/cm2
  • none of the above.

  • 61. 
    The advantage of multistage compression over single stage compression is

  • lower power consumption per unit of air delivered
  • higher volumetric efficiency
  • decreased discharge temperature
  • moisture free air
  • all of the above.

  • 62. 
    Pick up the wrong statement about advantages of multistage compression

  • better lubrication is possible advantages of multistage
  • more loss of air due to leakage past the cylinder
  • mechanical balance is better
  • air can be cooled perfectly in between
  • more uniform torque, light cylinder and saving in work.

  • 63. 
    As the value of index ‘«’ is decreased, the volumetric efficiency will

  • increase
  • decrease
  • remain unaffected
  • may increase/decrease depending on compressor clearance
  • none of the above.

  • 64. 
    The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called

  • slip factor
  • velocity factor
  • velocity coefficient
  • blade effectiveness

  • 65. 
    Losses in a centrifugal compressor are due to

  • inlet losses
  • impeller channel losses
  • diffuser losses
  • all of the above
  • none of the above

  • 66. 
    The volumetric efficiency of a compressor falls roughly as follows for every 5°C increase in atmospheric temperature (e ) 10%.

  • 0.1%
  • 0.5%
  • 1%
  • 5%

  • 67. 
    The indicated work per unit mass of air delivered is

  • directly proportional to clearance volume
  • greatly affected by clearance volume
  • not affected by clearance volume
  • inversely proportional to clearance volume

  • 68. 
    Which is false statement about advantages of multistage compressor in comparison to single stage compressor

  • less power requirement
  • better mechanical balance
  • less loss of air due to leakage past the cylinder
  • more effective lubrication
  • lower volumetric efficiency.

  • 69. 
    The ratio of isentropic work to Euler work is known as

  • pressure coefficient
  • work coefficient
  • polytropic reaction
  • slip factor
  • compressor efficiency.

  • 70. 
    The criterion of the thermodynamic efficiency for rotary compressor is

  • isentropic compression
  • isothermal compression
  • polytropic compression
  • any one of the above
  • none of the above.

  • 71. 
    For supplying intermittent small quantity of air at high pressure, following compressor is best suited

  • centrifugal
  • reciprocating
  • axial
  • screw
  • turbo jet.

  • 72. 
    For minimum work in multistage compression, assuming same index of compression in all stages

  • work done in first stage should be more
  • work done in subsequent stages should increase
  • work done in subsequent stages should decrease
  • work done in all stages should be equal
  • work done in any stage is no criterion for minimum work but depends on other factors.

  • 73. 
    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

  • increase
  • decrease
  • remain unaffected
  • other factors control it
  • unpredictable.

  • 74. 
    Diffuser in a compressor is used to

  • increase velocity
  • make the flow stream-line
  • convert pressure energy into kinetic energy
  • convert kinetic energy into pressure energy
  • increase degree of reaction.

  • 75. 
    The ratio of isentropic work to euler’s work is known as

  • compressor efficiency
  • isentropic efficiency
  • Euler’s efficiency
  • pressure coefficient
  • pressure ratio.

  • 76. 
    The thermodynamic efficiency of rotary compressor is based on

  • isothermal compression
  • adiabatic compression
  • isentropic compression
  • polytropic compression
  • none of the above.

  • 77. 
    . Phenomenon of choking in compressor means

  • no flow of air
  • fixed mass flow rate regardless of pressure ratio
  • reducing mass flow rate with increase in pressure ratio
  • increased inclination of chord with air steam
  • does not occur.

  • 78. 
    . The maximum compression ratio in an actual single stage axial flow comperssor is of the order of

  • 1 : 1.2
  • 1 : 2
  • 1 : 5
  • 1 : 10
  • 1 : 1

  • 79. 
    . Maximum delivery pressure is a rotary air compressor is of the order of

  • 6 kg/cm2
  • 10 kg/cm2
  • 16 kg/cm2
  • 25 kg/cm2
  • 40 kg/cm2.

  • 80. 
    . Surging is the phenomenon of

  • air stream blocking the passage
  • motion of air at sonic velocity
  • unsteady, periodic and reversed flow
  • air stream not able to follow the blade contour
  • production of no air pressure.

  • 81. 
    . Pick up wrong statement. Surging phenomenon in centrifugal com-pressor depends on

  • mass flow rate
  • pressure ratio
  • change in load
  • stagnation pressure at the outlet
  • all of the above.

  • 82. 
    . The ratio of the increase in pressure in rotor blades to total increase in pressure in the stage is called

  • pressure ratio
  • pressure coefficient
  • degree of reaction
  • slip factor
  • stage factor.

  • 83. 
    . Axial flow compressor resembles

  • centrifugal pump
  • reciprocating pump
  • turbine
  • sliding vane compressor
  • none of the above.

  • 84. 
    . Axial flow compressor has the following advantage over centrifugal compressor

  • larger air handling ability per unit frontal area
  • higher pressure ratio per stage
  • aerofoil blades are used
  • higher average velocities
  • none of the above.

  • 85. 
    . Actual compression curve is

  • same as isothermal
  • same as adiabatic
  • better than isothermal and adiabatic
  • in between isothermal and adiabatic
  • none of the above.

  • 86. 
    . Atmospheric pressure is 1.03 kg/cm and vapour pressure is 0.03 kg/cm . The air pressure will be

  • 1.03 kg/cm2
  • 1.06 kg/cm2
  • 1.00 kg/cm2
  • 0.53 kg/cm2
  • 0.5 kg/cm2.

  • 87. 
    . The pressure ratio of an ideal vaned compressor with increase in mass flow rate

  • increases
  • decreases
  • remains constant
  • first decreases and then increases
  • unpredictable.

  • 88. 
    . Rotary compressors are suitable for

  • large discharge at high pressure
  • low discharge at high pressure
  • large discharge at low pressure
  • low discharge at low pressure
  • there is no such limitation.

  • 89. 
    . The vloumetric efficiency of compressor with increase in compression ratio will

  • increase
  • decrease
  • remain same
  • may increase/decrease depending on clearance volume
  • none of the above.

  • 90. 
    . Stalling of blades in axial flow compressor is the phenomenon of

  • air stream blocking the passage
  • motion of air at sonic velocity
  • unsteady periodic and reversed flow
  • air stream not able to follow the blade contour
  • production of no air pressure.

  • 91. 
    . Pick up the wrong statement

  • centrifugal compressors deliver prac-tically constant pressure over a considerable range of capacities
  • Axial flow compressors have a sub-stantially constant delivery at variable pressures
  • centrifugal compressors have a wider stable operating range than axial flow compressors
  • axial flow compressors are bigger in diameter compared to centrifugal type
  • axial flow compressors apt to be longer as compared to centrifugal type.

  • 92. 
    . The work ratio of a gas turbine plant is defined as the ratio of

  • net work output and heat supplied (6) net work output and work done by tur¬bine
  • actual heat drop and isentropic heat drop
  • net work output and isentropic heat drop
  • isentropic increase/drop in tempera¬ture and actual increase/ drop in temperature.

  • 93. 
    . Gas turbine works on

  • Brayton or Atkinson cycle
  • Carnot cycle
  • Rankine cycle
  • Erricsson cycle
  • Joule cycle.

  • 94. 
    . The work ratio of simple gas turbine cycle depends on

  • pressure ratio
  • maximum cycle temperature
  • minimum cycle temperature
  • all of the above
  • none of die above.

  • 95. 
    . The pressure ratio for an open cycle gas turbine compared to closed cycle gas turbine of same h.p. is

  • low
  • high
  • same
  • low/high depending on make and type
  • unpredictable.

  • 96. 
    . Open cycle gas turbine works on (6) Rankine cycle

  • Brayton or Atkinson cycle
  • Carnot cycle
  • Erricsson cycle
  • Joule cycle.

  • 97. 
    . The fuel consumption in gas turbines is accounted for by

  • low.er heating value
  • higher heating value
  • heating value
  • higher calorific value
  • highest calorific value.

  • 98. 
    . Gas turbines for power generaion are normally used

  • to supply base load requirements
  • to supply peak load requirements
  • to enable start thermal power plant
  • in emergency
  • when other sources of power fail.

  • 99. 
    . Mechanical efficiency of gas turbines as compared to I.C engines is

  • higher
  • lower
  • same
  • depends on on odier considerations
  • unpredictable.

  • 100. 
    . The ratio of specific weighf/h.p. of gas turbin and I.C engines may be typically of the order of

  • 1 : 1
  • 2 : 1
  • 4 : 1
  • 1:2
  • 1 : 6.

  • 101. 
    . The thermal efficiency of a gas turbine as compared to a diesel plant is

  • same
  • more
  • less
  • depends on other factors
  • unpredictably.

  • 102. 
    . The air-fuel ratio in gas turbines is of the order of

  • 7 : 1
  • 15 : 1
  • 30 : 1
  • 40 : 1
  • 50: 1.

  • 103. 
    . The pressure ratio in gas turbines is of the order of

  • 2:l
  • :1
  • 61: 1
  • 9 : 1
  • 12:1.

  • 104. 
    . The hottest point in a gas turbine is

  • at the base
  • at the tip
  • in the center
  • between ~ to i of the blade height
  • uniformly heated.

  • 105. 
    . The following is true for an open cycle gas turbine having exhaust heat exchanger. Atmospheric air before entering the compressor is

  • heated
  • compressed air before entering the combustion chamber is heated
  • bled gas from turbine is heated and readmitted for complete expansion
  • exhaust gases drive the compressor
  • part of exhaust gases are heated and mixed up with atmospheric air to utilise exhaust heat.

  • 106. 
    . Gas turbine blades are given a rake

  • equal to zero
  • in the direction of motion of blades
  • opposite to the direction of motion of blades
  • depending on the velocity
  • none of the above.

  • 107. 
    . Efficiency of gas turbine is increased by

  • reheating
  • inter cooling
  • adding a regenerator
  • all of the above
  • none of the above.

  • 108. 
    . Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is

  • higher
  • lower
  • equal
  • can’t be compared
  • unpredictable.

  • 109. 
    . The ideal efficiency of simple gas turbine cycle depends on

  • pressure ratio
  • maximum cycle temperature
  • minimum cycle temperature
  • all of the above
  • none of the above.

  • 110. 
    . The thermal efficiency of a simple gas turbine for a given turbine inlet temperature with increase in pressure ratio

  • increases
  • decreases
  • first increases and then decreases
  • first decreases and then increases
  • remains same.

  • 111. 
    . Gas turbines use following type of air compressor

  • centrifugal type
  • reciprocating type
  • lobe type
  • axial flow type
  • none of the above.

  • 112. 
    . As the turbine inlet temperature increases, the thermal efficiency of gas turbine for the optimum pressure ratio

  • increases
  • decreases
  • remains same
  • first increases and then decreases
  • first decreases and then increases.

  • 113. 
    . There is a certain pressure ratio (optimum) for a gas turbine at which its thermal efficiency is maximum. With increase in turbine temperature, the value of pressure ratio for the peak efficiency would

  • remain same
  • decrease
  • increase
  • unpredictable
  • none of the above.

  • 114. 
    . The material commonly used for air craft gas turbine is

  • stainless steel
  • high alloy’ steel
  • duralumin
  • Timken, Haste and Inconel allpys
  • titanium.

  • 115. 
    . The jnaximum combustion pressure in gas turbine as compared to I.C. engine is

  • more
  • less
  • same
  • depends on other factors
  • unpredictable.

  • 116. 
    . For an irreversible gas turbine cycle, the efficiency and work ratio both depend on

  • pressure ratio alone
  • maximum cycle temperature alone
  • minimum cycle temperature alone
  • both pressure ratio and maximum cycle temperature
  • none of the above.

  • 117. 
    . Producer gas is produced by

  • carbonisation of coal
  • passing steam over incandescent coke
  • passing air and a large amount of steam over waste coal at about 65°C
  • partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
  • same way as the natural gas.

  • 118. 
    . Water gas is produced by

  • carbonisation of coal
  • passing steam over incandescent coke
  • passing air and a large amount of steam over waste coal at about 65°C
  • partial combustion of caol, eke, anthractie coal or charcoal in a mixed air steam blast
  • same way as the natural gas.

  • 119. 
    Water is injected in gas turbine cycle to

  • control temperature
  • control output of turbine
  • control fire hazards
  • increase efficiency
  • it is never done.

  • 120. 
    . A gas turbine used in air craft should have

  • high h.p. and low weight
  • low weight and small frontal area
  • small frontal area and high h.p.
  • high speed and high h.p.
  • all of the above.

  • 121. 
    . The closed cycle in gas turbines

  • provides greater flexibility
  • provides lesser flexibility
  • in never used
  • is used when gas is to be burnt
  • none of the above.

  • 122. 
    . In the axial flow gas turbine, the work ratio is the ratio of

  • compressor work and turbine work
  • output and input
  • actual total head tempeature drop to the isentrpic total head drop from total head inlet to static head outlet
  • actual compressor work and theoretical comprssor work
  • none of the above.

  • 123. 
    . The degree of reaction of an axial flow turbine is the ratio of isentropic temperature drop in a blade row to the

  • adiabatic temperature drop in the stage
  • total temperature drop
  • total temperature drop in the stage
  • total adiabaitc temperature drop
  • difference of maximum and minimum temperature in the cycle.

  • 124. 
    . If infinite number of heaters be used in a gas turbine, then expansion process in turbine approaches

  • isothermal
  • isentropic
  • adiabatic
  • isochoric
  • isobaric.

  • 125. 
    . Pick up the correct statement

  • gas turbine uses low air-fuel ratio to economise on fuel
  • gas turhine uses high air-fuel ratio to reduce outgoing temperature
  • gas turbine uses low air-fuel ratio to develop the high thrust required
  • all of the above
  • none of the above.

  • 126. 
    Intercooling in gas turbine results in

  • increase in net output but decrease in thermal efficiency
  • increase in thermal efficiency but decrease in net output
  • increase in both thermal efficiency and net output
  • decrease in both thermal efficiency and net output
  • none of the above.

  • 127. 
    . If V, U and Vr represent the absolute velocity of fluid, velocity of blade, and relative velocity of fluid, and suffix i and o stand for entry and exit conditions, then in a rotary machine whose degree of reaction is unity

  • i=V0
  • t>V0
  • U,
  • ,= U0
  • Vri=Vm.

  • 128. 
    . Pick up the wrong statement

  • large gas turbines employ axial flow compressors
  • axial flow compressors are more stable than centrifugal type compressors but not as efficient
  • axial flow compressors have high capacity and efficiency
  • axial flow compressors have instability region of operation
  • centrifugal compressors are used mainly on low flow pressure ratio gas turbines.

  • 129. 
    . The power available for take off and climb in case of turbojet engine as compared to reciprocating engine is

  • less
  • more
  • same
  • may be less or more depending on ambient conditons
  • unpredictable.

  • 130. 
    . Pick up the correct statement

  • large gas turbines use radial inflow turbines
  • gas turbines have their blades similar to steam turbine
  • gas .turbine’s blade will appear as impulse section at the hub and as a reaction section at tip
  • gas turbines use both air and liquid cooling
  • all of the above are correct.

  • 131. 
    . A closed gas turbine in which fuel is burnt directly in the air is not possible because of

  • high pressure ratio
  • increasing gas temperature
  • high specific volume
  • high friction losses
  • paucity of 02.

  • 132. 
    . Choose the correct statement

  • gas turbine requires lot of cooling water
  • gas turbine is capable of rapid start up and loading
  • gas turbines have flat efficiency at part loads
  • gas turbines have high standby losses and require lot of maintenance
  • gas turbines can be used to generate power only.

  • 133. 
    . Ram compression in turbojet involves

  • reduction of speed of incoming air and conversion of part of it into pressure energy
  • compression of inlet air
  • increasing speed of incoming air
  • lost work
  • leakage losses.

  • 134. 
    . In gas turbines^ high thermal efficiency is obtained in

  • closed cycle
  • open cycle
  • both of the above
  • closed/open depending on other con-siderations
  • unpredictable.

  • 135. 
    . In the cross compounding of the gas turbine plant

  • h.p. compressor L connected to h.p. turbine and l.p. compressor ot l.p. tur-bine
  • h.p. compressor is connected to l.p. turbine and l.p. compressor is con-nected to h.p. turbine
  • both the arrangements can be employed
  • all are connected in series
  • none of the above.

  • 136. 
    A jet engine works on the principle of conservation of

  • mass
  • energy
  • flow
  • linear momentum
  • angular momentum.

  • 137. 
    . In jet engines, for the efficient production of large power, fuel is burnt in an atmosphere of

  • vacuum
  • atmospheric air
  • compressed air
  • oxygen alone
  • liquid hydrogen.

  • 138. 
    . Which of the following fuels can be used in turbojet engines

  • liquid hydrogne
  • high speed diesel oil
  • kerosene
  • demethylated spirit
  • methyl alcohol

  • 139. 
    . Turbo propeller has the^following additional feature over the turbojet

  • peopeller
  • diffuser
  • intercooler
  • turbine and combustion chamber
  • starting engine.

  • 140. 
    . Propulsive efficiency is defined as ratio of

  • thrust power and fuel energy
  • engine output and propulsive power
  • propulsive power and fuel input
  • thrust power and propulsive power
  • none of the above.

  • 141. 
    . In jet engines, paraffin is usually used as the fuel because of its

  • high calorific value
  • ease of atomisation
  • low freezing point
  • (a) and (c) above
  • none of the above.

  • 142. 
    . A rocket engine for the combustion of its fuel

  • carries its own oxygen
  • uses surrounding air
  • uses compressed atmospheric air
  • does not require oxygen
  • depends on electrical energy supplied by solar cells.

  • 143. 
    . A rocket works with maximum overall efficiency when air craft velocity is equal to the

  • jet velocity
  • twice the jet velocity
  • half the jet velocity
  • average of the jet velocity
  • no such co-relationship with jet velocity exists.

  • 144. 
    . Propulsion efficiency of the following order-is obtained in practice (ti) 34%

  • 50%
  • 60%
  • 72%
  • 85%.

  • 145. 
    . The maximum propulsion efficiency of a turbojet is attained at around following speed –

  • 550 km/hr
  • 1050km/hr
  • 1700 km/hr
  • 2400km /hr
  • 4000 km/hr.

  • 146. 
    In jet propulsion power unit, the inlet duct of diverging shape is used in order to

  • collect more air
  • convert kinetic energy of air into pres-sure energy
  • provide robust structure
  • beautify the shape
  • none of the above

  • 147. 
    . In jet engines the products of combustion after passing through the gas lurbine are discharged into

  • atmosphere
  • back to the compressor
  • discharge nozzle
  • vacuum
  • none of the above.

  • 148. 
    . The air entry velocity m a rocket as compared to aircraft is

  • same
  • more
  • less
  • zero
  • dependent on power and speed.

  • 149. 
    . The weight per horse power ratio for gas. turbine as compared to I.C. engine and steam turbine is

  • same
  • higher
  • lower
  • uncomparable
  • unpredictable.

  • 150. 
    . Fighter bombers use following type of engine

  • turbo-jet
  • turbo-propeller
  • rocket
  • ram-jet ,
  • pulsojet.

  • 151. 
    Pick up the wrong statement

  • pulsojet requires no ambient air for propulsion
  • ramjet-engine has no turbine
  • turbine drives compressor in a burbojet
  • bypass turbo-jet engine increases the thrust without adversely affecting, the propulsive efficiency and fuel economy
  • propeller is an indirect reaction device.

  • 152. 
    . The blades of gas turbine are made of

  • mild steel
  • stainless steel
  • carbon steel
  • high alloy seel
  • high nicket alloy (neimonic).

  • 153. 
    . The following property is most important for material used for gas turbine blade

  • toughness
  • fatigue
  • creep
  • corrosion resistance
  • bulk modulus.

  • 154. 
    . The effective power of gas turbines is increased by adding the following in compressor

  • ammonia and water vapour
  • carbon dioxide
  • nitrogen
  • hydrogen
  • none of the above.

  • 155. 
    . High air-fuel ratio is used in gas turbines

  • to increase the output
  • to increase the efficiency
  • to save fuel
  • to reduce the exit temperature
  • none of the above.

  • 156. 
    . Air-fuel ratio in a jet engine will be of the order of

  • 10: 1
  • 15: 1
  • 20 : 1
  • 60 : 1
  • 100 : 1.

  • 157. 
    . In which case the air-fuel ratio is likely to be maximum

  • 2-stroke engine
  • 4-stroke petrol engine
  • 4-stroke diesef engine
  • multi-cylinder engine
  • gas turbine.

  • 158. 
    . In jet engines the compression ratio

  • varies as square root of the speed
  • Varies linearly to the speed
  • varies as square of the speed
  • varies as cube of the speed
  • is constant irrespective of variation in speed.

  • 159. 
    . The specific output per kg mass flow rate of a gas turbine (having fixed efficiencies of compressor and turine and fixed higher and lower temperature) with increase in pressure ratio will

  • increase first at fast rate and then slow
  • increase first at slow rate and then fast
  • decrease continuously
  • first increase, reach maximum and then decrease
  • none of the above.

  • 160. 
    . The working fluid in ai turbine is

  • in two phases
  • in three phases
  • in a single phase
  • in the form of air and water mixture
  • gas and no air.

  • 161. 
    . Gas turbine cycle with regenerator

  • increases thermal efficiency
  • allows high compression ratio
  • decreases heat loss is exhaust
  • allows operation at very high altitudes
  • permits high moisture content fuel to be used.

  • 162. 
    . The compression ratio in a gas turbine is of the roder of

  • 3.5 : 1
  • 5 : 1
  • 8 : 1
  • 12 : 1
  • 20 : 1.

  • 163. 
    . Reheating in multistage expansion gas turbine results in

  • high thermal efficiency
  • reduction in compressor work
  • decrease of heat loss in exhaust
  • maximum work output
  • none of the above.

  • 164. 
    . The main purpose of reheating in gas turbine is to

  • increase temperature
  • reduce turbine size
  • increase power output
  • increase speed
  • increase pressure ratio.

  • 165. 
    . Reheating in gas turbine results in

  • increase of work ratio
  • decrease of thermal efficiency
  • decrease of work ratio
  • both (a) and (b) above
  • both (b) and (c) above.

  • 166. 
    . Work ratio of a gas turbine plant is ratio of

  • net work output and work done by turbine
  • net work output and heat supplied
  • work done by turbine and heat supplied
  • work done by turbine and net work output
  • actual/heat drop and isentropic heat drop.

  • 167. 
    . Work ratio of a gas turbine may be improved by f

  • decreasing the compression work
  • increasing the compression work
  • increasing the turbine work
  • decreasing the turbine work
  • (a) and (c) above.

  • 168. 
    . Maximum temprature in a gas turbine is of the order of COMPRESSORS, GAS TURBINES AND JET ENGINES

  • 2500°C
  • 2000°C
  • 1500°C
  • 1000°C
  • 700°C.

  • 169. 
    . In the aircraft propellers

  • the propulsive matter is caused to flow around the propelled body
  • propulsive matter is ejected from within the propelled body
  • its functioning does not depend on presence of air
  • all of the above
  • none of the above.

  • 170. 
    . In air breathing jet engine, the jet is formed by expading

  • gases
  • solids
  • liquid
  • plasma
  • highly heated atmospheric air.

  • 171. 
    . Ram-jet engine

  • is self-operating at zero flight speed
  • is not self-operating at zero^flight speed
  • requires no air for its operation
  • produces a jet consisting of plasma
  • none of the above.

  • 172. 
    . For speed above 3000 km/hour, it is more advantageous to use

  • turbo-jet engine
  • ram-jet engine
  • propellers
  • rockets
  • hydraulic jet propulsion.

  • 173. 
    . A simple turbo-jet engine is basically

  • a propeller system
  • gas-turbine engine equipped with a propulsive nozzle and diffuse*
  • chemical rocket regine
  • ram-jet enigne
  • none of the above.

  • 174. 
    . Which of the following plants is smallest and lightest for genrating a given amount of power

  • steam power plant
  • petrol engine
  • diesel engine’
  • solar plant
  • gas turbine plant.

  • 175. 
    . In turbo fan engine, the jet velocity as compared to turbo-jet engine is

  • less
  • more
  • same
  • may be less or more depening upon speed
  • none of the above.

  • 176. 
    . Turbofan engine employs

  • one air stream
  • two or more air streams
  • no air stream
  • solid fuel firing
  • rocket principle for its operation.

  • 177. 
    . Pressure ratio in gas turbines is the ratio of

  • compressor pressure ratio
  • highest pressure to exhaust pressure
  • inlet pressure to exhaust pressure
  • pressures across the turbine
  • none of the above.

  • 178. 
    . Pick up the false statement

  • gas turbine is a self-starting unit
  • gas turbine does not require huge quantity of water like steam plant
  • exhaust losses in gas turbine are high due to large mass flow rate
  • overall efficiency of gas turbine plant is lower than that of a reciprocating engine
  • gas turbine can be easily started and stopped and thus is best suited for peaking demands.

  • 179. 
    The efficiency and work ratio of a gas turbine plant can be increased by

  • using mulit-stage compressor with mfercooler
  • adding heat exchanger
  • injecting water in/around combustion chamber
  • reheating the air after partial expansion in the turbine
  • all of the above.

  • 180. 
    . Pick up the correct statement

  • closed cycle gas turbine is an I.C engine
  • gas turbine uses same working fluid over and over again
  • air-fuel ratio in a gas turbine is 100 : 1
  • ideal efficiency of closed cycle gas turbine plant is more than carnot cycle efficiency
  • thrust in turbo-jet is produced by nozzle exit gases.

  • 181. 
    . The compression ratio in a jet engine varies proportional to

  • speed
  • speed
  • altitude
  • Vspeed
  • does not Vary.

  • 182. 
    . The efficiency of jet engine is

  • higher at ground
  • higher at high altitudes
  • same at all altitudes
  • higher at high speed
  • lower at low speed.
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