# Mechanical Engineering-Compressors, Gas Turbines and Jet Engines Important MCQ PDF

1. 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
(e) 25°C, 1 kg/cm2 and relative humidity of 50%.
Ans: a2. Standard air is the air at
(a) atmospheric conditions at any specific
location
(b) 20°C and 1 kg/cm2 and relative humidity
36%
(c) 0°C and standard atmospheric conditions
(d) 15°C and 1 kg/cm2
(e) 25°C, 1 kg/cm2 and RH of 60%.
Ans: b

3. 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
(e) 3.2 kg.
Ans: c

4. Adiabatic compression is one in which
(a) temperature during compression remains
constant
(b) no heat leaves or enters the compressor
cylinder during cornpression
(c) temperature rise follows a linear
relationship
(d) work done is maximum
(e) entropy decreases.
Ans: b

5. The capacity of a compressor is 5 m /mih.
5 m /min refers to
(a) standard air
(b) free air
(c) compressed air
(d) compressed air at delivery pressure
(e) air sucked.
Ans: b

6. The overall isothermal eiffciency 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
(e) isothermal work to ideal work.
Ans: a

7. The- most efficient method of compressing
air is to compress it
(a) isothermally
(c) isentropically
(d) isochronically
(e) as per law pV
Ans: a

8. Maximum work is done in compressing air
when the compression is
(a) isothermal
(c) polytropic
(d) any one of the above
(e) none of the above.
Ans: b

9. 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 more than atmospheric and temperature slightly less than
atmospheric
(e) pressure sightly less than atmospheric and temperature slightly more than
atmospheric.
Ans: e

10. Isothermal compression effeicency 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
(e) isothermally.
Ans: b

11. The compressor capacity with decrease in
suction temperature
(a) increases
(b) decreases
(c) remains unaffected
(d) may increase or decrease depending on
compressor capacity
(e) increases upto certain limit and then
decreases.
Ans: a

12. Isothermal compression efficiency, even
when running at high speed, can be approached by using
(a) multi-stage compression
(b) cold water spray
(c) both (a) and (b) above
(d) fully insulating the cylinder
(e) high stroke.
Ans: c

13. Compression efficiency is compared
against
(a) ideal compression
compression
(d) isentropic compression
(e) isothermal compression.
Ans: e

14. Aeroplanes employ following type of
compressor
(b) axial flow
(c) centrifugal
(d) combination of above
(e) none of the above.
Ans: b

15. 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
(e) prevents   compressor  jacket
running very hot.
Ans: b

16. 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
and two constant volume
(e) two isobaric,  two adiabatic and one
constant volume.
Ans: a

17. 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
and  one constant volume,
(d) one adiabatic, one isobaric and two
constant volume
and one constant volume.
Ans: b

18. 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
(e)  0.75 m3/mt.
Ans: a

19. The work done per unit mass of air in
compression will’be least when n is equal to
(a) 1
(b) 1.2     ,
(c) 1.3
(d) 1.4
(e) 1.5
Ans: a

20. Isothermal compression though most
efficient, but is not -practicable because
(a) ityrequires 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
(e) it requires cylinder to be placed in
water.
Ans: d

21. Ratio of indicated H.P. and brake H.P. is
known as
(a) mechanical efficiency
(b) volumetric efficiency
(c) isothermal efficiency
(e) relative efficiency.
Ans: a

22. The ratio of work doen 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
(e) compressor effectiveness.
Ans: d

23. Cylinder clearance in a compressor should
be
(a) as large as possible
(b) as small as possible
(c) about 50% of swept volume
(d) about 100% of swept volume
(e) none of the above.
Ans: b

24. Ratio of compression is the ratio of
(a) gauge discharge pressure to the gauge
intake pressure
(b) absolute discharge pressure to the
ab-solute intake pressure
(c) pressures at discharge and suction
cor-responding to same temperature
(d) stroke volume and clearance volume
(e) none of the above.
Ans: b

25. Clearance volume in actual reciprocating
compressors is essential
(a) to accommedate Valves in the cylinder
(b) to provide cushioning effect
(c) to attain high volumetric efficiency
(d) to avoid mechanical bang of piston with
(e) to provide cushioning effect and also to
avoid mechanical bang of piston with cylinder head.
Ans: e

26. The net work input required for
compressor with increase in clearance volume
(a) increases
(b) decreases
(c) remains same
(d) increases/decreases depending on
com-pressor capacity
(e) unpredictable.
Ans: c

27. Ratio of indicated h.p. to shaft h.p. in
known as
(a) compressor efficiency
(b) isothermal efficiency
(c) volumetric efficiency
(d) mechanical efficiency
Ans: d

28. 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
(e) proportional to compression ratio.
Ans: b

29. Volumetric efficiency of air compressors
is of the order of
(a) 20-30%
(b) 40-50%
(c) 60-70%
(d) 70-90%
(e) 90-100%.
Ans: d

30. Volumetric efficiency of a compressor
with clearance volume
(a) increases with increase in compression
ratio
(b) decreases with increase in compression
ratio
(c) in  not  dependent  upon
compression ratio
(d) may  increase/decrease depending
on compressor capacity
(e) unpredictable.
Ans: b

31. 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 compressin ratio
(d) may  increase/decrease
depending  on compressor capacity
(e) unpredictable.
Ans: c

32. 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
(e) none of the above.
Ans: b

33. Euler’s equation is applicable for
(a) centrifugal compressor
(b) axial compressor
(c) pumps
(d) all of the above
(e) none of the above.
Ans: d

40. 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
(e) from any one of the above locations.
Ans: d

41. Mining industry usually employs following
motive power
(a) A.C. electric motor
(b) compressed air
(c) petrol engine
(d) diesel engine
(e) D.C. electric motor.
Ans: b

42. Which is false statement about air
(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
(e) These reduce frequent on/off operation of
compressors.
Ans: c

44. An air receiver is to be placed outside.
Should it be placed in
(a) sun
(c) rain
(d) enclosed room
(e) anywhere.
Ans:b

45. 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
(e) Outlet temperature is reduced.
Ans: b

46. In multistage compressor, the isothermal
compression is achieved by
(a) employing intercooler
(b) by constantly cooling the cylinder
(c) by running compressor at very slow speed
(d) by insulating the cylinder
(e) none of the above.
Ans: c

47. Reciprocating air 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
(e) any one of the above.
Ans: a

48. 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
(e) any one of the above.
Ans: d

49. The capacity of compressor will be
highest when its intake temperature is
(a) lowest
(b) highest
(c) anything.
(d) atmospheric
(e) none of the above.
Ans: d

50. 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
(e) increase pressure.
Ans: c

51. To aviod moisture troubles, the
compressed air main line should
(a) rise gradually towards the point of use
(b) drop gradually towards the point of use
(c) be laid vertically
(d) be laid exactly horizontally
(e) none of the above
Ans: b

52. Separators in compressor installations
are located
(a) before intercooler
(b) after intercooler
(d) between after-cooler and air receiver
(e) before suction.
Ans: d

53. The area of actual indicator diagram on
an air compressor as compared to area of ideal indicator diagram is
(a) less
(b) more
(c) same
(d) more/less depending on compressor
capacity
(e) unpredictable.
Ans: b

54. An air compressor may be controlled by
(a) throttle control (b) clearance control
(c) blow-off control
(d) any one of the above
(e) none of the above.
Ans: d

55. The compressor efficiecny is the
(a) isothermal H.P/indicated H.R
(b) isothermal H.P./shaft H.R
(c) total output/air input
(d) compression work/motor input
(e) none Of the above.
Ans: a

56. To avoid moisture troubles, the branch
connections from compressed air lines should be taken from
(a) top side of main
(b) bottom side of main
(c) left side of main
(d) right side of main
(e) any location.
Ans: a

57. The thrust on the rotor in a centrifugal
compressor is produced by
(b) axial component
(c) tangential component
(d) resultant component
Ans: b

58. The compressor performance at higher
altitude compared to sea level will be
(a) same
(b) higher
(c) lower
(d) dependent on other factors
(e) none of the above.
Ans: c

59. A compressor at high altitude will draw
(a) more power
(b) less power
(c) same power
(d) more/less power depending on other
factors
(e) none of the above.
Ans: b

60. During peak load periods, the best method
of controlling compressors is
(a) start-stop motor
(c) relief valve
(d) variable speed
(e) none of the above.
Ans: b

61. A centrifugal compressor works on the
principle of
(a) conversion   of  pressure
energy   into kinetic energy
(b) conversion of kinetic energy into
pres¬sure energy
(c) centripetal action
(d) generating pressure directly
(e) combination of (a) and (d).
Ans: b

62. For a compressor, least work will be done
if the compression is
(a) isentropic
(b) isothermal
(c) polytropic
(d) somewhere in between isentropic and
isothermal
(e) none of the above.
Ans: b

67. In a compressor, free air delivered is
the actual volume delivered at the stated pressure reduced to
(d) N.T.P. conditions
(b) intake temperature and pressure
conditions
(c) 0°C and 1 kg/cm2
(d) 20°C and 1 kg/cm2
(e) none of the above.
Ans: b

68. The volumetirc efficiency of a compressor
is calculated on the basis of
(a) volume of air inhaled at working
conditions
(b) volume of air inhaled at N.T.P.
conditions
(c) volume at 0°C and 1 kg/cm2
(d) volume at 20°C and 1 kg/cm2
(e) none of the above.
Ans: b

69. The volumetric efficiency of a compressor
falls roughly as follows for every 100 m increase in elevation
(a) 0.1%
(b) 0.5%
(c) 1.0%
(d) 5%
(e) 10%.
Ans: c

70. 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 semirotary type
(c) disc or feather type
(d) any of the above
(e) none of the above.
Ans: c

71. During base load operation, the best
method of controlling compressor is
(a) start-stop motor
(c) relief valve
(d) variable speed
(e) none of the above.
Ans: a

72. More than one stage will be preferred for
reciprocating compressor if the delivery pressure is more than
(a) 2 kg/cm2
(b) 6 kg/cm2
(c) 10 kg/cm2
(d) 14.7 kg/cm2
(e) none of the above.
Ans: a

73. 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) moisture free air
(e)     all of the above.
Ans: e

74. Pick up the wrong statement about
(a) better lubrication is possible advantages
of multistage
(b) more loss of air due to leakage past the
cylinder
(c) mechanical balance is better
(d) air can be cooled perfectly in between
(e) more uniform torque, light cylinder and
saving in work.
Ans: b

75. As the value of index ‘«’ is decreased,
the volumetric efficiency will
(a) increase
(b) decrease
(c) remain unaffected
(d) may  increase/decrease
depending  on compressor clearance
(e) none of the above.
Ans: b

76. 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
Ans: a

79. Losses in a centrifugal compressor are
due to
(a) inlet losses
(b) impeller channel losses
(c) diffuser losses
(d) all of the above
(e) none of the above
Ans: d

80. 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%
(e ) 10%.
Ans: c

81. 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
Ans: c

89. For actual single stage centrifugal
compressor, the maximum pressure ratio is of the order of
(a) 1 : 1.2
(b) 1 : 2
(c) 1 : 4
(d) 1 : 10
(e) 1 : 1
Ans:

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) more effective lubrication
(e) lower volumetric efficiency.
Ans: e

91. The ratio of isentropic work to Euler
work is known as
(a) pressure coefficient
(b) work coefficient
(c) polytropic reaction
(d) slip factor
(e) compressor efficiency.
Ans: a

92. The criterion of the thermodynamic
efficiency for rotary compressor is
(a) isentropic compression
(b) isothermal compression
(c) polytropic compression
(d) any one of the above
(e) none of the above.
Ans: a

93. For supplying intermittent small quantity
of air at high pressure, following compressor is best suited
(a) centrifugal
(b) reciprocating
(c) axial
(d) screw
(e) turbo jet.
Ans: b

94. 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
(e) work done in any stage is no criterion for minimum work but depends on
other factors.
Ans: d

95. 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
(e) unpredictable.
Ans: a

96. Diffuser in a compressor is used to
(a) increase velocity
(b) make the flow stream-line
(c) convert pressure energy into kinetic
energy
(d) convert kinetic energy into pressure
energy
(e) increase degree of reaction.
Ans: d

98. The ratio of isentropic work to euler’s
work is known as
(a) compressor efficiency
(b) isentropic efficiency
(c) Euler’s efficiency
(d) pressure coefficient
(e) pressure ratio.
Ans: d

99. The thermodynamic efficiency of rotary
compressor is based on
(a) isothermal compression
(c) isentropic compression
(d) polytropic compression
(e) none of the above.
Ans: b

100. 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
(e) does not occur.
Ans: b

101. The maximum compression ratio in an
actual single stage axial flow comperssor is of the order of
(a) 1 : 1.2
(b) 1 : 2
(c) 1 : 5
(d) 1 : 10
(e) 1 : 1
Ans: a

102. 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
(e) 40 kg/cm2.
Ans: b

103. Surging is the phenomenon of
(a) air stream blocking the passage
(b) motion of air at sonic velocity
(c) unsteady, periodic and reversed flow
contour
(e) production of no air pressure.
Ans: c

104. Pick up wrong statement.
Surging phenomenon in centrifugal com-pressor depends on
(a) mass flow rate
(b) pressure ratio
(d) stagnation pressure at the outlet
(e) all of the above.
Ans: d

105. 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
(e) stage factor.
Ans: c

106. Axial flow compressor resembles
(a) centrifugal pump
(b) reciprocating pump
(c) turbine
(d) sliding vane compressor
(e) none of the above.
Ans: c

107. Axial flow compressor has the following
(a) larger air handling  ability  per  unit
frontal area
(b) higher pressure ratio per stage
(d) higher average velocities
(e) none of the above.
Ans: a

108. Actual compression curve is
(a) same as isothermal
(c) better than isothermal and adiabatic
(d) in between isothermal and adiabatic
(e) none of the above.
Ans: d

109. Atmospheric pressure is 1.03 kg/cm and
vapour pressure is 0.03 kg/cm . The air pressure will be
(a) 1.03 kg/cm2
(b) 1.06 kg/cm2
(c) 1.00 kg/cm2
(d) 0.53 kg/cm2
(e) 0.5 kg/cm2.
Ans: c

110. The pressure ratio of an ideal vaned
compressor with increase in mass flow rate
(a) increases
(b) decreases
(c) remains constant
(d) first decreases and then increases
(e) unpredictable.
Ans: c

111. 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
(e) there is no such limitation.
Ans: c

112. The vloumetric efficiency of compressor
with increase in compression ratio will
(a) increase
(b) decrease
(c) remain same
(d) may increase/decrease depending on
clearance volume
(e) none of the above.
Ans: b

113. Stalling of blades in axial flow
compressor is the phenomenon of
(a) air stream blocking the passage
(b) motion of air at sonic velocity
(c) unsteady periodic and reversed flow
contour
(e) production of no air pressure.
Ans: d

114. Pick up the wrong statement
(a) centrifugal compressors deliver prac-tically constant pressure
over a considerable range of capacities
(b) Axial flow compressors have a sub-stantially constant
delivery at variable pressures
(c) centrifugal compressors have a wider
stable operating range than axial flow compressors
(d) axial flow compressors are bigger in
diameter compared to centrifugal type
(e) axial flow compressors apt to be longer
as compared to centrifugal type.
Ans: d

115. The work ratio of a gas turbine plant is
defined as the ratio of
(a) net work output and heat supplied (6) net work output and work done by
tur¬bine
(c) actual heat drop and isentropic heat drop
(d) net work output and isentropic heat drop
(e) isentropic increase/drop in tempera¬ture
and actual increase/ drop in temperature.
Ans: b

116. Gas turbine works on
(a) Brayton or Atkinson cycle
(b) Carnot cycle
(c)     Rankine cycle
(d) Erricsson cycle
(e) Joule cycle.
Ans: a

117. The work ratio of simple gas turbine
cycle depends on
(a) pressure ratio
(b) maximum cycle temperature
(c) minimum cycle temperature
(d) all of the above
(e) none of die above.
Ans: d

118. 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
(e) unpredictable.
Ans: a

119. Open cycle gas turbine works on
(a) Brayton or Atkinson cycle
(6) Rankine cycle
(c) Carnot cycle
(d) Erricsson cycle
(e) Joule cycle.
Ans: a

120.  The fuel consumption in gas turbines is accounted for by
(a) low.er heating value
(b) higher heating value
(c) heating value
(d) higher calorific value
(e) highest calorific value.
Ans: a

121. Gas turbines for power generaion are
normally used
(a) to supply base load requirements
(b) to supply peak load requirements
(c) to enable start thermal power plant
(d) in emergency
(e) when other sources of power fail.
Ans: b

122. Mechanical efficiency of gas turbines as
compared to I.C engines is
(a) higher
(b) lower
(c) same
(d) depends on on odier considerations
(e) unpredictable.
Ans: a

123. The ratio of specific weighf/h.p. of gas
turbin and I.C engines may be typically of the order of
(a) 1 : 1
(b) 2 : 1
(c) 4 : 1
(d) 1:2
(e) 1 : 6.
Ans: e

124. The thermal efficiency of a gas turbine
as compared to a diesel plant is
(a) same
(b) more
(c) less
(d) depends on other factors
(e) unpredictably.
Ans: c

125. The air-fuel ratio in gas turbines is of
the order of
(a) 7 : 1
(b) 15 : 1
(c) 30 : 1
(d) 40 : 1
(e) 50: 1.
Ans: e

126. The pressure ratio in gas turbines is of
the order of
(a),2:l
(b)4:1
(c) 61: 1
(d) 9 : 1
(e) 12:1.
Ans: c

128. The hottest point in a gas turbine is
(a) at the base
(b) at the tip
(c) in the center
(d) between ~ to i of the blade height
(e) uniformly heated.
Ans: d

129. The following is true for an open cycle
gas turbine having exhaust heat exchanger. Atmospheric air before entering the
compressor is
(a) heated
(b) compressed air before entering the
combustion chamber is heated
(c) bled gas from turbine is heated and readmitted
for complete expansion
(d) exhaust gases drive the compressor
(e) part of exhaust gases are heated and
mixed up with atmospheric air to utilise exhaust heat.
Ans: b

130. 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
(d) depending on the velocity
(e) none of the above.
Ans: b

131. Efficiency of gas turbine is increased
by
(a) reheating
(b) inter cooling
(d) all of the above
(e) none of the above.
Ans: c

132. Temperature of gases at end of
compression as compared to exhaust gases in a gas turbine is
(a) higher
(b) lower
(c) equal
(d) can’t be compared
(e) unpredictable.
Ans: b

133. The ideal efficiency of simple gas
turbine cycle depends on
(a) pressure ratio
(b) maximum cycle temperature
(c) minimum cycle temperature
(d) all of the above
(e) none of the above.
Ans: a

134. The thermal efficiency of a simple gas
turbine for a given turbine inlet temperature with increase in pressure ratio
(a) increases
(b) decreases
(c) first increases and then decreases
(d) first decreases and then increases
(e) remains same.
Ans: a

135. Gas turbines use following type of air
compressor
(a) centrifugal type
(b) reciprocating type
(c) lobe type
(d) axial flow type
(e) none of the above.
Ans: d

136. As the turbine inlet temperature
increases, the thermal efficiency of gas turbine for the optimum pressure ratio
(a) increases
(b) decreases
(c) remains same
(d) first increases and then decreases
(e) first decreases and then increases.
Ans: a

137. 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
(a) remain same
(b) decrease
(c) increase
(d) unpredictable
(e) none of the above.
Ans: c

138. The material commonly used for air craft
gas turbine is
(a) stainless steel
(b) high alloy’ steel
(c) duralumin
(d) Timken, Haste and Inconel allpys
(e) titanium.
Ans: d

139. 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
Ans: c

140. The combustion efficiency of a gas
turbine using perfect combustion chamber is of the order of
(a) 50%
(b) 75%
(c) 85%
(d) 90%
(e ) 99%.
Ans: e

141. The jnaximum combustion pressure in gas
turbine as compared to I.C. engine is
(a) more
(b) less
(c) same
(d) depends on other factors
(e) unpredictable.
Ans: b

142. 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
(e) none of the above.
Ans: d

143. Producer gas is produced by
(a) carbonisation of coal
(b) passing steam over incandescent coke
(c) passing air and a large amount of steam
over waste coal at about 65°C
(d) partial combustion of coal, coke,
anthracite coal or charcoal in a mixed air steam blast
(e) same way as the natural gas.
Ans: d

144. Water gas is produced by
(a) carbonisation of coal
(b) passing steam over incandescent coke
(c) passing air and a large amount of steam
over waste coal at about 65°C
(d) partial combustion of caol, eke,
anthractie coal or charcoal in a mixed air steam blast
(e) same way as the natural gas.
Ans: b

14 Water is injected in gas turbine cycle to
(a) control temperature
(b) control output of turbine
(c) control fire hazards
(d) increase efficiency
(e) it is never done.
Ans: b

146. A gas turbine used in air craft should
have
(a) high h.p. and low weight
(b) low weight and small frontal area
(c) small frontal area and high h.p.
(d) high speed and high h.p.
(e) all of the above.
Ans: b

148. 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
(e) none of the above.
Ans: a

149. In the axial flow gas turbine, the work
ratio is the ratio of
(a) compressor work and turbine work
(b) output and input
(c) actual total head tempeature drop to the
(d) actual compressor work and theoretical
(e) none of the above.
Ans: c

150. The degree of reaction of an axial flow
turbine is the ratio of isentropic temperature drop in a blade row to the
(a) adiabatic temperature drop in the stage
(b) total temperature drop
(c) total temperature drop in the stage
(e) difference of maximum and minimum
temperature in the cycle.
Ans: c

153. If infinite number of heaters be used in
a gas turbine, then expansion process in turbine approaches
(a) isothermal
(b) isentropic
(d) isochoric
(e) isobaric.
Ans: a

154. Pick up the correct statement
(a) gas turbine uses low air-fuel ratio to
economise on fuel
(b) gas turhine 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
(e) none of the above.
Ans: b

15 Intercooling in gas turbine results in
(a) increase in net output but decrease in
thermal efficiency
(b) increase   in   thermal
efficiency  but decrease in net output
(c) increase in both thermal efficiency and
net output
(d) decrease in both thermal efficiency and
net output
(e) none of the above.
Ans: a

156. 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
(a)Vi=V0
(b)Vt>V0
(c) U,<V0
(d)V,= U0
(e) Vri=Vm.
Ans: a

157. Pick up the wrong statement
(a) large gas turbines employ axial flow compressors
(b) axial flow compressors are more stable
than centrifugal type compressors but not as efficient
(c) axial flow compressors have high capacity
and efficiency
(d) axial   flow   compressors
have   instability region of operation
(e) centrifugal compressors are used mainly
on low flow pressure ratio gas turbines.
Ans: b

158. The power available for take off and
climb in case of turbojet engine as compared to reciprocating engine is
(a) less
(b) more
(c) same
(d) may be less or more depending on ambient
conditons
(e) unpredictable.
Ans: a

159. 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
(e) all of the above are correct.
Ans: c

160. A closed gas turbine in which fuel is
burnt directly in the air is not possible because of
(a) high pressure ratio
(b) increasing gas temperature
(c) high specific volume
(d) high friction losses
(e) paucity of 02.
Ans: e

161. Choose the correct statement
(a) gas turbine requires lot of cooling water
(b) gas turbine is capable of rapid start up
(c) gas turbines have flat efficiency at part
(d) gas turbines have high standby losses and require lot of maintenance
(e) gas turbines can be used to generate power only.
Ans: b

162. Ram compression in turbojet involves
(a) reduction of speed of incoming air and
conversion of part of it into pressure energy
(b) compression of inlet air
(c) increasing speed of incoming air
(d) lost work
(e) leakage losses.
Ans: a

163. 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
con-siderations
(e) unpredictable.
Ans: a

164. In the cross compounding of the gas turbine
plant
(a) h.p. compressor L connected to h.p.
turbine and l.p. compressor ot l.p. tur-bine
(b) h.p. compressor is connected to l.p.
turbine and l.p. compressor is con-nected to h.p. turbine
(c) both the arrangements can be employed
(d)  all are connected in series
(e) none of the above.
Ans: b

16 A jet engine works on the principle of
conservation of
(a) mass
(b) energy
(c) flow
(d) linear momentum
(e) angular momentum.
Ans: d

166. In jet engines, for the efficient
production of large power, fuel is burnt in an atmosphere of
(a) vacuum
(b) atmospheric air
(c) compressed air

(d) oxygen alone
(e) liquid hydrogen.
Ans: c

167. Which of the following fuels can be used
in turbojet engines
(a) liquid hydrogne
(b) high speed diesel oil
(c) kerosene
(d) demethylated spirit
(e) methyl alcohol
Ans: c

168. Turbo propeller has the^following
(a) peopeller
(b) diffuser
(c) intercooler
(d) turbine and combustion chamber
(e) starting engine.
Ans: a

169. 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
(e) none of the above.
Ans: d

170. 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) (a) and (c) above
(e) none of the above.
Ans: d

171. 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
(e) depends on electrical energy supplied by
solar cells.
Ans: a

172. 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
(e) no such co-relationship with jet velocity
exists.
Ans: c

173. Propulsion efficiency of the following
order-is obtained in practice
(ti) 34%
(b) 50%
(c) 60%
(d) 72%
(e) 85%.
Ans: c

174. The maximum propulsion efficiency of a
turbojet is attained at around following speed –
(a) 550 km/hr
(b) 1050km/hr
(c) 1700 km/hr
(d) 2400km /hr
(e) 4000 km/hr.
Ans: d

17 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
pres-sure energy
(c) provide robust structure
(d) beautify the shape
(e) none of the above
Ans: b

176. In jet engines the products of combustion after passing through the gas lurbine
are discharged into
(a) atmosphere
(b) back to the compressor
(c) discharge nozzle
(d) vacuum
(e) none of the above.
Ans: c

177. The air entry velocity m a rocket as compared to aircraft is
(a) same
(b) more
(c) less
(d) zero
(e) dependent on power and speed.
Ans: d

183. The weight per horse power ratio for
gas. turbine as compared to I.C. engine and steam turbine is
(a) same
(b) higher
(c) lower
(d) uncomparable
(e) unpredictable.
Ans: c

184. Fighter bombers use following type of
engine
(a) turbo-jet
(b) turbo-propeller
(c) rocket
(d) ram-jet ,
(e) pulsojet.
Ans: a

18 Pick up the wrong statement
(a) pulsojet requires no ambient air for
propulsion
(b) ramjet-engine has no turbine
(c) turbine drives compressor in a burbojet
(d) bypass turbo-jet engine increases the thrust without adversely affecting,
the propulsive efficiency and fuel economy
(e) propeller is an indirect reaction device.
Ans: a

186. Thrust of a jet propulsion power unit
can be increased by
(a) burning fuel after gas turbine
(b) injecting water in the compressor
(c) injecting ammonia into the combustion
chamber
(d) all of the three above
(e) none of the above.
Ans:

(a) mild steel
(b) stainless steel
(c) carbon steel
(d) high alloy seel
(e) high nicket alloy (neimonic).
Ans: e

188.The following property is most important for material used for gas
(a) toughness
(b) fatigue
(c) creep
(d) corrosion resistance
(e) bulk modulus.
Ans: c

189. The effective power of gas turbines is
increased by adding the following in compressor
(a) ammonia and water vapour
(b) carbon dioxide
(c) nitrogen
(d) hydrogen
(e) none of the above.
Ans: a

190. High air-fuel ratio is used in gas
turbines
(a) to increase the output
(b) to increase the efficiency
(c) to save fuel
(d) to reduce the exit temperature
(e) none of the above.
Ans: d

191. Air-fuel ratio in a jet engine will be
of the order of
(a) 10: 1
(b) 15: 1
(c) 20 : 1
(d) 60 : 1
(e) 100 : 1.
Ans: d

192. In which case the air-fuel ratio is
likely to be maximum
(a) 2-stroke engine
(b) 4-stroke petrol engine
(c) 4-stroke diesef engine
(d) multi-cylinder engine
(e) gas turbine.
Ans: e

193. In jet engines the compression ratio
(a) varies as square root of the speed
(b) Varies linearly to the speed
(c) varies as square of the speed
(d) varies as cube of the speed
(e) is constant irrespective of variation in
speed.
Ans: c

194. 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
(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
(e) none of the above.
Ans: d

19 The working fluid in ai turbine is
(a) in two phases
(b) in three phases
(c) in a single phase
(d) in the form of air and water mixture
(e) gas and no air.
Ans: c

196. 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
(e) permits high moisture content fuel to be
used.
Ans: a

197. The compression ratio in a gas turbine
is of the roder of
(a) 3.5 : 1
(b) 5 : 1
(c) 8 : 1
(d) 12 : 1
(e) 20 : 1.
Ans: c

198. Reheating in multistage expansion gas
turbine results in
(a) high thermal efficiency
(b) reduction in compressor work
(c) decrease of heat loss in exhaust
(d) maximum work output
(e) none of the above.
Ans: d

199. The main purpose of reheating in gas
turbine is to
(a) increase temperature
(b) reduce turbine size
(c) increase power output
(d) increase speed
(e) increase pressure ratio.
Ans: c

200. Reheating in gas turbine results in
(a) increase of work ratio
(b) decrease of thermal efficiency
(c) decrease of work ratio
(d) both (a) and (b) above
(e) both (b) and (c) above.
Ans: d

201. Work ratio of a gas turbine plant is
ratio of
(a) net work output and work done by turbine
(b) net work output and heat supplied
(c) work done by turbine and heat supplied
(d) work done by turbine and net work output
(e) actual/heat drop and isentropic heat
drop.
Ans: a

202. Work ratio of a gas turbine may be
improved by f
(a) decreasing the compression work
(b) increasing the compression work
(c) increasing the turbine work
(d) decreasing the turbine work
(e) (a) and (c) above.
Ans: e

203. Maximum temprature in a gas turbine is
of the order of COMPRESSORS, GAS TURBINES AND JET ENGINES
(a) 2500°C
(b) 2000°C
(c) 1500°C
(d) 1000°C
(e) 700°C.
Ans: e

21 In the aircraft propellers
(a) the propulsive matter is caused to flow around
the propelled body
(b) propulsive matter is ejected from within
the propelled body
(c) its functioning does not depend on
presence of air
(d) all of the above
(e) none of the above.
Ans: d

216. In air breathing jet engine, the jet is
(a) gases
(b) solids
(c) liquid
(d) plasma
(e) highly heated atmospheric air.
Ans: e

217. Ram-jet 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
(e) none of the above.
Ans: b

218. For speed above 3000 km/hour, it is more
(a) turbo-jet engine
(b) ram-jet engine
(c) propellers
(d) rockets
(e) hydraulic jet propulsion.
Ans: b

219. A simple turbo-jet engine is basically
(a) a propeller system
(b) gas-turbine engine equipped with a
propulsive nozzle and diffuse*
(c) chemical rocket regine
(d) ram-jet enigne
(e) none of the above.
Ans: b

220. Which of the following plants is
smallest and lightest for genrating a given amount of power
(a) steam power plant
(b) petrol engine
(c) diesel engine’
(d) solar plant
(e) gas turbine plant.
Ans: e

221. In turbo fan engine, the jet velocity as
compared to turbo-jet engine is
(a) less
(b) more
(c) same
(d) may be less or more depening upon speed
(e) none of the above.
Ans: a

222. Turbofan engine employs
(a) one air stream
(b) two or more air streams
(c) no air stream
(d) solid fuel firing
(e) rocket principle for its operation.
Ans: b

223. Pressure ratio in gas turbines is the
ratio of
(a) compressor pressure ratio
(b) highest pressure to exhaust pressure
(c) inlet pressure to exhaust pressure
(d) pressures across the turbine
(e) none of the above.
Ans: b

224. 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
(e) gas turbine can be easily started and
stopped and thus is best suited for peaking demands.
Ans: a

22 The efficiency and work ratio of a gas
turbine plant can be increased by
(a) using mulit-stage compressor with
mfercooler
(c) injecting water in/around combustion
chamber
(d) reheating the air after partial expansion in the turbine
(e) all of the above.
Ans: e

226. Pick up the correct statement
(a) closed cycle gas turbine is an I.C engine
(b) gas turbine uses same working fluid over and over again
(c) air-fuel ratio in a gas turbine is 100 :
1
(d) ideal efficiency of closed cycle gas
turbine plant is more than carnot cycle efficiency
(e) thrust in turbo-jet is produced by nozzle
exit gases.
Ans: e

227. The  compression  ratio
in  a jet engine varies proportional to
(a) speed
(b) speed
(c) altitude
(d) Vspeed
(e) does not Vary.
Ans: b

228. The efficiency of jet engine is
(a) higher at ground
(b) higher at high altitudes
(c) same at all altitudes
(d) higher at high speed
(e) lower at low speed.
Ans: b