Compressors, Gas Turbines And Jet Engines MCQs : This section focuses on the "Compressors, Gas Turbines And Jet Engines". These Multiple Choice Questions (MCQs) should be practiced to improve the Compressors, Gas Turbines And Jet Engines skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.
Question 1
The compression ratio for the compressor is always _________ unity.
A. Equal to
B. Less than
C. More than
D. None of these
Question 2
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
Question 3
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
Question 4
The fuel consumption in gas turbines is accounted for by
A. Lower heating value
B. Higher heating value
C. Heating value
D. Higher calorific value
Question 5
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
Question 6
Which of the following plants is smallest and lightest for generating a given amount of power?
A. Gas turbine plant
B. Petrol engine
C. Diesel engine
D. Solar plant
Question 7
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
Question 8
Gas turbine blades are given a rake
A. Equal to zero
B. In the direction of motion of blades
C. Opposite to the direction of motion of blades
D. Depending on the velocity
Question 9
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
Question 10
An air compressor may be controlled by
A. Throttle control
B. Clearance control
C. Blow off control
D. Any one of the above
Question 11
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
D. Total adiabatic temperature drop
Question 12
The net work input required for compressor with increase in clearance volume
A. Increases
B. Decreases
C. Remains same
D. Increases/decreases depending on compressor capacity
Question 13
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
Question 14
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
Question 15
Compression efficiency is compared against
A. Ideal compression
B. Adiabatic compression
C. Isentropic compression
D. Isothermal compression
Question 16
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
Question 17
Reheating in a multistage expansion gas turbine ________ compressor work.
A. Has no effect on
B. Decreases
C. Increases
D. None of these
Question 18
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
Question 19
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
Question 20
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. None of the above
Question 21
Ratio of indicated h.p. to shaft h.p. in known as
A. Compressor efficiency
B. Isothermal efficiency
C. Volumetric efficiency
D. Mechanical efficiency
Question 22
Ratio of indicated H.P. and brake H.P. is known as
A. Mechanical efficiency
B. Volumetric efficiency
C. Isothermal efficiency
D. Adiabatic efficiency
Question 23
The output of a gas turbine is 300 KW and its efficiency is 20 percent, the heat supplied is
A. 6000 KW
B. 15 KW
C. 600 KW
D. 150 KW
Question 24
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
Question 25
The air power of the compressor is also known as
A. Indicated power
B. Brake power
C. Frictional power
D. None of these
Question 26
To avoid 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
Question 27
The ratio of the discharge pressure to the inlet pressure of air is called
A. Compression ratio
B. Expansion ratio
C. Compressor efficiency
D. Volumetric efficiency
Question 28
A machine used to raise the pressure of air is called
A. Gas turbine
B. I.C engine
C. Compressor
D. Air motor
Question 29
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
Question 30
The volume of air delivered in a medium capacity air compressor per unit time is
A. 0.1 to 1.2 m³/s
B. 0.15 to 5 m³/s
C. Above 5 m³/s
D. None of these
Question 31
The inter-cooler pressure, for minimum work required, for a two stage reciprocating air compressor, is given by (where p₁ = Intake pressure of air, p₂ = Inter-cooler pressure, and p₃ = Delivery pressure of air)
A. p₂ = p₁ × p₃
B. p₂ = p₁/p₃
C. p₂ = p₁ × p₂
D. p₂ = p₃/p₁
Question 32
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
Question 33
For perfect intercooling in a three stage compressor
A. p₂/p₁ = p₃/p₂ = p₄/p₃
B. p₃/p₁ = p₄/p₂
C. p₁ p₂ = p₃ p₄
D. p₁ p₃ = p₂ p₄
Question 34
For perfect intercooling in a two stage compressor
A. p₂/p₁ = p₃/p₂
B. p₁/p₃ = p₂/p₁
C. p₁ = p3
D. p₁ = p₂ p3
Question 35
The weight per horse power ratio for gas in Turbine as compared to I.C. engine and steam turbine is
A. Same
B. Higher
C. Lower
D. None of these
Question 36
The volume of air sucked by the compressor during its suction stroke is called
A. Free air delivery
B. Compressor capacity
C. Swept volume
D. None of these
Question 37
A centrifugal compressor works on the principle of
A. Conversion of pressure energy into kinetic energy
B. Conversion of kinetic energy into pressure energy
C. Centripetal action
D. Generating pressure directly
Question 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
Question 39
Water is injected in gas turbine cycle to
A. Control temperature
B. Control output of turbine
C. Control fire hazards
D. Increase efficiency
Question 40
Gas turbine works on
A. Brayton or Atkinson cycle
B. Carnot cycle
C. Rankine cycle
D. Ericsson cycle
Question 41
A closed cycle gas turbine works on
A. Carnot cycle
B. Rankine cycle
C. Ericsson cycle
D. Joule cycle
Question 42
Open cycle gas turbine works on
A. Brayton or Atkinson cycle
B. Rankine cycle
C. Carnot cycle
D. Ericsson cycle
Question 43
A turboprop is preferred to turbojet because
A. It has high propulsive efficiency at high speeds
B. It can fly at supersonic speeds
C. It can fly at high elevations
D. It has high power for take off
Question 44
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
Question 45
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
Question 46
The ratio of the net work obtained from the gas turbine plant to the turbine work is known as
A. Compression ratio
B. Work ratio
C. Pressure ratio
D. None of these
Question 47
The ratio of isentropic work to Euler work is known as
A. Pressure coefficient
B. Work coefficient
C. Polytropic reaction
D. Slip factor
Question 48
The ratio of isentropic work to Euler’s work is known as
A. Compressor efficiency
B. Isentropic efficiency
C. Euler
D. Pressure coefficient
Question 49
In a single acting reciprocating compressor, the suction, compression and delivery of air takes place in ________ of the piston.
A. One stroke
B. Two strokes
C. Three strokes
D. Four strokes
Question 50
The overall thermal efficiency of an ideal gas turbine plant is (where r = Pressure ratio)
A. r ɣ-1
B. 1 - r ɣ-1
C. 1 - (1/r) ɣ-1/ɣ
D. 1 - (1/r) ɣ/ɣ-1
Question 51
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.
Question 52
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
Question 53
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
Question 54
A jet engine has
A. No propeller
B. Propeller in front
C. Propeller at back
D. Propeller on the top
Question 55
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
Question 56
Propulsion efficiency of the following order is obtained in practice
A. 34%
B. 50%
C. 60%
D. 72%
Question 57
In a closed cycle gas turbine, the air is compressed
A. Isothermally
B. Polytropically
C. Isentropically
D. None of these
Question 58
In a double acting compressor, the air is compressed
A. In one cylinder
B. In two cylinders
C. In a single cylinder on both sides of the piston
D. In two cylinders on both sides of the piston
Question 59
The work-done on a compressor will be minimum if air is taken from
A. The atmosphere
B. A source at 0° C
C. A source of low temperature air
D. A source of high temperature air
Question 60
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
Question 61
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
Question 62
The overall efficiency of the compressed air system is the
A. Ratio of shaft output of the air motor to the shaft input to the compressor
B. Ratio of shaft input to the compressor to the shaft output of air motor
C. Product of shaft output of air motor and shaft input to the compressor
D. None of the above
Question 63
In a jet engine, the air-fuel ratio is
A. 30:1
B. 40:1
C. 50:1
D. 60:1
Question 64
The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is
A. Pressure drop across the valves
B. Superheating in compressor
C. Clearance volume and leakages
D. All of these
Question 65
Turbofan engine employs
A. One air stream
B. Two or more air streams
C. No air stream
D. Solid fuel firing
Question 66
Gas turbines for power generation 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
Question 67
The criterion of the thermodynamic efficiency for rotary compressor is
A. Isentropic compression
B. Isothermal compression
C. Polytropic compression
D. None of the above
Question 68
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
Question 69
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 coal, eke, anthracite coal or charcoal in a mixed air steam blast
Question 70
Which of the following statement is wrong?
A. In a two stage reciprocating air compressor with complete intercooling, maximum work is saved
B. The minimum work required for a two stage reciprocating air compressor is double the work required for each stage
C. The ratio of the volume of free air delivery per stroke to the swept volume of the piston is called volumetric efficiency
D. None of the above
Question 71
Work ratio of a gas turbine may be improved by
A. Decreasing the compression work
B. Increasing the compression work
C. Increasing the turbine work
D. Both (A) and (C) above
Question 72
The gas in cooling chamber of a closed cycle gas turbine is cooled at
A. Constant volume
B. Constant temperature
C. Constant pressure
D. None of these
Question 73
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
Question 74
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
Question 75
The mean effective pressure of the compressor is the
A. Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B. Volume of air delivered by the compressor
C. Volume of air sucked by the compressor during its suction stroke
D. None of the above
Question 76
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
Question 77
An after-cooler is used to
A. Remove impurities from air
B. Reduce volume of air
C. Cause moisture and oil vapour to drop out
D. Cool the air
Question 78
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. Ideal efficiency of closed cycle gas turbine plant is more than Carnot cycle efficiency
D. Thrust in turbojet is produced by nozzle exit gases
Question 79
Choose the correct statement
A. Gas turbine requires lot of cooling water
B. Gas turbine is capable of rapid start up and loading
C. Gas turbines has flat efficiency at part loads
D. Gas turbines have high standby losses and require lot of maintenance
Question 80
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
Question 81
Pick up the correct statement
A. Gas turbine uses low air-fuel ratio to economise on fuel
B. Gas turbine uses high air-fuel ratio to reduce outgoing temperature
C. Gas turbine uses low air-fuel ratio to develop the high thrust required
D. All of the above
Question 82
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.
Question 83
The compressor capacity with decrease in suction temperature
A. Increases
B. Decreases
C. Remain unaffected
D. May increase or decrease depending on compressor capacity
Question 84
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
Question 85
The overall isothermal efficiency of the compressor is defined as the ratio of
A. Work required to compress the air isothermally to the actual work required to compress the air for the same pressure ratio
B. Isothermal power to the shaft power or B.P. of the motor or engine required to drive the compressor
C. Volume of free air delivery per stroke to the swept volume of the piston
D. Isentropic power to the power required to drive the compressor
Question 86
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
Question 87
The work ratio of a gas turbine plant is defined as the ratio of
A. Net work output and heat supplied
B. Net work output and work done by turbine
C. Actual heat drop and isentropic heat drop
D. Net work output and isentropic heat drop
Question 88
The maximum propulsion efficiency of a turbojet is attained at around following speed
A. 550 km/hr
B. 1050 km/hr
C. 1700 km/hr
D. 2400 km/hr
Question 89
The minimum work required for a three stage reciprocating air compressor is ________ the work required for each stage.
A. Equal to
B. Double
C. Three times
D. Six times
Question 90
The working fluid in a turbine is
A. In two phases
B. In three phases
C. In a single phase
D. In the form of air and water mixture
Question 91
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
Question 92
An air receiver is to be placed outside. Should it be placed in
A. Sun
B. Shade
C. Rain
D. Enclosed room
Question 93
The velocity of air entering in a rocket is _________ as compared to an aircraft.
A. Zero
B. Less
C. More
D. Same
Question 94
In open cycle turbojet engines used in military aircraft, reheating the exhaust gas from the turbine by burning, more fuel is used to increase the
A. Thrust and range of aircraft
B. Efficiency of the engine
C. Both (A) and (B)
D. None of these
Question 95
The efficiency of the vane blower is (where W₁ = Workdone due to compression, and W₂ = Workdone due to back flow)
A. W₁/(W₁ + W₂)
B. W₂/(W₁ + W₂)
C. (W₁ + W₂)/W₁
D. (W₁ + W₂)/W₂
Question 96
A compressor at high altitudes will require ________ power.
A. Same
B. Less
C. More
D. None of these
Question 97
In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into
A. Atmosphere
B. Vacuum
C. Discharge nozzle
D. Back to the compressor
Question 98
In jet engines the products of combustion after passing through the gas turbine are discharged into
A. Atmosphere
B. Back to the compressor
C. Discharge nozzle
D. Vacuum
Question 99
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
Question 100
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
Question 101
Efficiency of gas turbine is increased by
A. Reheating
B. Inter cooling
C. Adding a regenerator
D. All of the above
Question 102
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
Question 103
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
Question 104
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
Question 105
Pick up the wrong statement
A. Pulse-jet requires no ambient air for propulsion
B. Ramjet engine has no turbine
C. Turbine drives compressor in a Turbojet
D. Bypass turbojet engine increases the thrust without adversely affecting, the propulsive efficiency and fuel economy
Question 106
Pick up the wrong statement
A. Centrifugal compressors deliver practically constant pressure over a considerable range of capacities
B. Axial flow compressors have a substantially 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
Question 107
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
Question 108
The volumetric efficiency of a compressor falls roughly as follows for every 100 m increase in elevation
A. 0.10%
B. 0.50%
C. 1.00%
D. 5%
Question 109
The air entry velocity m a rocket as compared to aircraft is
A. Same
B. More
C. Less
D. Zero
Question 110
The compressor efficiency 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
Question 111
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
Question 112
In air compressors, free air delivery means the
A. Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B. Volume of air delivered by the compressor
C. Volume of air sucked by the compressor during its suction stroke
D. None of the above
Question 113
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
Question 114
Which of the following statement is correct?
A. The reciprocating compressors are best suited for high pressure and low volume capacity
B. The effect of clearance volume on power consumption is negligible for the same volume of discharge
C. Both (A) and (B)
D. None of these
Question 115
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
Question 116
The temperature of air at the beginning of the compression stroke is ________ the atmospheric temperature.
A. Equal to
B. Less than
C. More than
D. None of these
Question 117
When the outlet angle from the rotor of a centrifugal compressor is more than 90°, then the blades are said to be
A. Forward curved
B. Backward curved
C. Radial
D. None of these
Question 118
The volumetric efficiency of compressor with increase in compression ratio will
A. Increase
B. Decrease
C. Remain same
D. May increase or decrease depending on clearance volume
Question 119
The thermodynamic efficiency of rotary compressor is based on
A. Isothermal compression
B. Adiabatic compression
C. Isentropic compression
D. Polytropic compression
Question 120
The ratio of work-done per cycle to the stroke volume of the compressor is known as
A. Compressor capacity
B. Compression ratio
C. Compressor efficiency
D. Mean effective pressure
Question 121
The specific output per kg mass flow rate of a gas turbine (having fixed efficiencies of compressor and turbine and fixed higher and lower temperature) with increase in pressure ratio will
A. Increase first at fast rate and then slow
B. Increase first at slow rate and then fast
C. Decrease continuously
D. First increase, reach maximum and then decrease
Question 122
In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to
A. N.T.P. conditions
B. Intake temperature and pressure conditions
C. 0°C and 1 kg/cm²
D. 20°C and 1 kg/cm²
Question 123
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
Question 124
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
Question 125
A jet engine works on the principle of conservation of
A. Mass
B. Energy
C. Flow
D. Linear momentum
Question 126
A compressor mostly used for supercharging of I.C. engines is
A. Radial flow compressor
B. Axial flow compressor
C. Roots blower
D. Reciprocating compressor
Question 127
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
Question 128
The degree of reaction is usually kept ________ for all types of axial flow compressors.
A. 0.2
B. 0.3
C. 0.4
D. 0.5
Question 129
The material commonly used for air craft gas turbine is
A. Stainless steel
B. High alloy steel
C. Duralumin
D. Timken, Haste alloys
Question 130
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
Question 131
The following property is most important for material used for gas turbine blade
A. Toughness
B. Fatigue
C. Creep
D. Corrosion resistance
Question 132
The main purpose of reheating in gas turbine is to
A. Increase temperature
B. Reduce turbine size
C. Increase power output
D. Increase speed
Question 133
In the cross compounding of the gas turbine plant
A. H.P. compressor is connected to H.P. turbine and L.P. compressor to L.P. turbine
B. H.P. compressor is connected to L.P. turbine and L.P. compressor is connected to H.P. turbine
C. Both the arrangements can be employed
D. All are connected in series
Question 134
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
Question 135
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
Question 136
A simple turbojet engine is basically
A. A propeller system
B. Gas turbine engine equipped with a propulsive nozzle and diffuse
C. Chemical rocket engine
D. Ramjet engine
Question 137
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
Question 138
Maximum work is done in compressing air when the compression is
A. Isothermal
B. Adiabatic
C. Polytropic
D. None of the above
Question 139
The volumetric efficiency of a compressor falls roughly as follows for every 5°C increase in atmospheric temperature
A. 0.10%
B. 0.50%
C. 1%
D. 5%
Question 140
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
Question 141
In a centrifugal compressor, the highest Mach number leading to shock wave in the fluid flow occurs at
A. Diffuser inlet radius
B. Diffuser outlet radius
C. Impeller inlet radius
D. Impeller outlet radius
Question 142
If the clearance ratio for a reciprocating air compressor is 'K', then its volumetric efficiency is given by
A. 1 - k + k (p₁/p₂)1/n
B. 1 + k - k (p₂/p₁)1/n
C. 1 - k + k (p₁/p₂) n- 1/n
D. 1 + k - k (p₂/p₁) n-1/n
Question 143
Axial flow compressor has the following advantage over centrifugal compressor
A. Larger air handling ability per unit frontal area
B. Higher pressure ratio per stage
C. Aerofoil blades are used
D. Higher average velocities
Question 144
The pressure ratio of an ideal vaned compressor with increase in mass flow rate
A. Increases
B. Decreases
C. Remain constant
D. First decreases and then increases
Question 145
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
Question 146
A closed cycle gas turbine consists of a
A. Compressor
B. Heating chamber
C. Cooling chamber
D. All of these
Question 147
During base load operation, the best method of controlling compressor is
A. Start-stop motor
B. Constant speed unloader
C. Relief valve
D. Variable speed
Question 148
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
Question 149
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
Question 150
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
Question 151
In a single acting reciprocating air compressor, without clearance, the compression of air may be
A. Isothermal
B. Polytropic
C. Isentropic
D. Any one of these
Question 152
The propulsive power of the rocket is (where v₁ = Jet velocity, and v₂ = Aircraft velocity)
A. (v₁² -v₂²)/2g
B. (v₁ - v₂)²/2g
C. (v₁² -v₂²)/g
D. (v₁ - v₂)²/g
Question 153
Euler's equation is applicable for
A. Centrifugal compressor
B. Axial compressor
C. Pumps
D. All of the above
Question 154
The compressor capacity is defined as the
A. Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B. Volume of air delivered by the compressor
C. Volume of air sucked by the compressor during its suction stroke
D. None of the above
Question 155
In a single stage, single acting reciprocating air compressor without clearance volume, the work-done is maximum during
A. Isothermal compression
B. Isentropic compression
C. Polytropic compression
D. None of these
Question 156
In a single stage, single acting reciprocating air compressor, without clearance volume, the work-done is minimum during
A. Isothermal compression
B. Isentropic compression
C. Polytropic compression
D. None of these
Question 157
In a centrifugal compressor, the flow of air is ________ to the axis of compressor.
A. Parallel
B. Perpendicular
C. Inclined
D. None of these
Question 158
The most efficient method of compressing air is to compress it
A. Isothermally
B. Adiabatically
C. Isentropically
D. Isochronically
Question 159
In a high pressure compressor, the delivery pressure is
A. 1 to 5 bar
B. 5 to 8 bar
C. 8 to 10 bar
D. 10 to 15 bar
Question 160
The capacity of compressor will be highest when its intake temperature is
A. Lowest
B. Highest
C. Anything
D. Atmospheric
Question 161
It is not possible to use closed gas turbine cycle in aeronautical engines because
A. It is inefficient
B. It is bulky
C. It requires cooling water for its operation
D. None of the above
Question 162
For slow speed large capacity compressor, following type of valve will be best suited
A. Poppet valve
B. Mechanical valve of the Corliss, sleeve, rotary or semi rotary type
C. Disc or feather type
D. Any of the above
Question 163
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
Question 164
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
Question 165
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
Question 166
A compressor at high altitude will draw
A. More power
B. Less power
C. Same power
D. More/less power depending on other factors
Question 167
In which case the air-fuel ratio is likely to be maximum?
A. Gas turbine
B. 4-stroke petrol engine
C. 4-stroke diesel engine
D. Multi cylinder engine
Question 168
With the decrease in compression ratio, the volumetric efficiency
A. Does not change
B. Increases
C. Decreases
D. First decrease and then increase
Question 169
For maximum work, the reheating should be done to an intermediate pressure of (Where p₁ = Maximum pressure, and p₂ = Minimum pressure)
A. (p₁ - p₂)/2
B. (p₁ + p₂)/2
C. p₁/p₂
D. p₁ p₂
Question 170
Inter-cooling in multistage compressors is done
A. To cool the air during compression
B. To cool the air at delivery
C. To enable compression in two stages
D. To minimize the work of compression
Question 171
The efficiency and work ratio of a gas turbine plant can be increased by
A. Adding heat exchanger
B. Injecting water in/around combustion chamber
C. Reheating the air after partial expansion in the turbine
D. All of the above
Question 172
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
Question 173
Euler's equation can be used for
A. Radial flow compressors
B. Axial flow compressors
C. Pumps
D. All of these
Question 174
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
Question 175
Ratio of compression is the ratio of
A. Gauge discharge pressure to the gauge intake pressure
B. Absolute discharge pressure to the absolute intake pressure
C. Pressures at discharge and suction corresponding to same temperature
D. Stroke volume and clearance volume
Question 176
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
Question 177
The efficiency of roots blower ________ with the increase in pressure ratio.
A. Decreases
B. Increases
C. Does not change
D. None of these
Question 178
During peak load periods, the best method of controlling compressors is
A. Start-stop motor
B. Constant speed unloader
C. Relief valve
D. Variable speed
Question 179
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
Question 180
Isothermal compression efficiency can be attained by running the compressor
A. At very high speed
B. At very slow speed
C. At average speed
D. At zero speed
Question 181
Fighter bombers use following type of engine
A. Turbojet
B. Turbo-propeller
C. Rocket
D. Ramjet
Question 182
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
Question 183
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
Question 184
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 temperature drop to the isentropic total head drop from total head inlet to static head outlet
D. Actual compressor work and theoretical compressor work
Question 185
Which of the following statement is correct relating to rocket engines?
A. The combustion chamber in a rocket engine is directly analogous to the reservoir of a supersonic wind tunnel
B. The stagnation conditions exist at the combustion chamber
C. The exit velocities of exhaust gases are much higher than those in jet engine
D. All of the above
Question 186
The power available for takeoff 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 conditions
Question 187
Gas turbines use following type of air compressor
A. Centrifugal type
B. Reciprocating type
C. Lobe type
D. Axial flow type
Question 188
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
Question 189
If p₁, is the pressure of air entering the L.P. cylinder and p₂ 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 D₁ = Dia. of L.P. cylinder, and D₂ = Dia. of H.P. cylinder)
A. D₁/D₂ = p₁ p₂
B. D₁/D₂ = p₁/p₂
C. D₁/D₂ = p₂/p₁
D. None of these
Question 190
In n₁ and n₂ 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 (W₁/W₂) with perfect intercooling is given by
A. W₁/W₂ = n₂(n₁ - 1)/n₁(n₂ - 1)
B. W₁/W₂ = n₁(n₂ - 1)/n₂(n₁ - 1)
C. W₁/W₂ = n₁/n₂
D. W₁/W₂ = n₂/n₁
Question 191
If p₁ is the pressure of air entering the L.P, cylinder and p₃ is the pressure of air leaving the H.P. cylinder, then the ratio of cylinder diameters for a single acting, two stage reciprocating compressor with complete intercooling is given by
A. D₁/D₂ = (p₁ p₃)1/2
B. D₁/D₂ = (p₁/p₃)1/4
C. D₁/D₂ = (p₁ p₃)1/4
D. D₁/D₂ = (p₃/p₁)1/4
Question 192
Volumetric efficiency of a compressor decreases with ________ in compression ratio.
A. Decrease
B. Increase
C. Remain same
D. Does not change
Question 193
In multistage compressor, the isothermal compression is achieved by
A. Employing inter-cooler
B. By constantly cooling the cylinder
C. By running compressor at very slow speed
D. By insulating the cylinder
Question 194
In a single stage, single acting reciprocating air compressor, without clearance, the work-done on the air during isentropic compression is ________ the heat required to raise the temperature of air from T₁ to T₂ at a constant pressure.
A. Equal to
B. Less than
C. Greater than
D. None of these
Question 195
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
Question 196
For supplying intermittent small quantity of air at high pressure, following compressor is best suited
A. Centrifugal
B. Reciprocating
C. Axial
D. Screw
Question 197
The thrust on the rotor in a centrifugal compressor is produced by
A. Radial component
B. Axial component
C. Tangential component
D. None of the above
Question 198
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
Question 199
Actual compression curve is
A. Same as isothermal
B. Same as adiabatic
C. Better than isothermal and adiabatic
D. In between isothermal and adiabatic
Question 200
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
Question 201
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
Question 202
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
Question 203
Axial flow compressor resembles
A. Centrifugal pump
B. Reciprocating pump
C. Turbine
D. Sliding vane compressor
Question 204
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
Question 205
Isothermal compression efficiency, even when running at high speed, can be approached by using
A. Multistage compression
B. Cold water spray
C. Both (A) and (B) above
D. Fully insulating the cylinder
Question 206
The capacity of a compressor is expressed in
A. kg/m²
B. kg/m³
C. m³/min
D. m³/kg
Question 207
Ramjet engine
A. Is self operating at zero flight speed
B. Is not self operating at zero flight speed
C. Requires no air for its operation
D. Produces a jet consisting of plasma
Question 208
The blades of gas turbine are made of
A. High nickel alloy
B. Stainless steel
C. Carbon steel
D. High alloy steel
Question 209
The 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
Question 210
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
Question 211
For a two stage reciprocating compressor, compression from p₁ to p₃ is with perfect intercooling and no pressure losses. If compression in both the cylinders follows the same polytropic process and the atmospheric pressure is pa, then the intermediate pressure p₂ is given by
A. p₂ = (p₁ + p₃)/2
B. p₂ = p₁. p₃
C. P₂ = Pa × p₃/p₁
D. p₂ = Pa p₃/p₁
Question 212
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 = Vo
B. Vt > Vo
C. U < Vo
D. V = Uo
Question 213
The air is delivered ________ in one revolution in case of a three lobbed rotor.
A. Two times
B. Three times
C. Four times
D. Six times
Question 214
Losses in a centrifugal compressor are due to
A. Inlet losses
B. Impeller channel losses
C. Diffuser losses
D. All of the above
Question 215
Pick up wrong statement. Surging phenomenon in centrifugal compressor depends on
A. Mass flow rate
B. Pressure ratio
C. Change in load
D. Stagnation pressure at the outlet
Question 216
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
Question 217
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
Question 218
In air breathing jet engine, the jet is formed by expanding
A. Highly heated atmospheric air
B. Solids
C. Liquid
D. Plasma
Question 219
In a four stage compressor, if the pressure at the first and third stage is 1 bar and 16 bar, then the delivery pressure at the fourth stage will be
A. 1 bar
B. 16 bar
C. 64 bar
D. 256 bar
Question 220
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
Question 221
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
Question 222
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
Question 223
The combustion efficiency of a gas turbine using perfect combustion chamber is of the order of
A. 75%
B. 85%
C. 90%
D. 99%
Question 224
The compression ratio in a gas turbine is of the order of
A. 3.5 : 1
B. 5 : 1
C. 8 : 1
D. 12 : 1
Question 225
The pressure ratio in gas turbines is of the order of
A. 2: 1
B. 4:1
C. 61: 1
D. 9: 1
Question 226
Volumetric efficiency of air compressors is of the order of
A. 20 - 30%
B. 40 - 50%
C. 60 - 70%
D. 70 - 90%
Question 227
The air-fuel ratio in gas turbines is of the order of
A. 7: 1
B. 15: 1
C. 30: 1
D. 50: 1.
Question 228
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
Question 229
Maximum temperature in a gas turbine is of the order of
A. 700°C
B. 2000°C
C. 1500°C
D. 1000°C
Question 230
The maximum compression ratio in an actual single stage axial flow compressor is of the order of
A. 1 : 1.2
B. 1 : 2
C. 1 : 5
D. 1 : 10
Question 231
The inlet pressure is always ________ the discharge pressure.
A. Equal to
B. Less than
C. More than
D. None of these
Question 232
The compressor performance at higher altitude compared to sea level will be
A. Same
B. Higher
C. Lower
D. Dependent on other factors
Question 233
Separators are generally used in air compressor installations
A. Before the inter-cooler
B. After the inter-cooler
C. Between the after-cooler and receiver
D. Before first stage suction
Question 234
A 3 m³/min compressor means that it
A. Compresses 3 m³/min of standard air
B. Compresses 3 m³/ min of free air
C. Delivers 3 m³/ min of compressed air
D. Delivers 3 m³/ min of compressed air at delivery pressure
Question 235
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
Question 236
The pressure of air at the beginning of the compression stroke is ________ the atmospheric pressure.
A. Equal to
B. Less than
C. More than
D. None of these
Question 237
A closed gas turbine in which fuel is burnt directly in the air is not possible because of
A. Paucity of O2
B. Increasing gas temperature
C. High specific volume
D. High friction losses
Question 238
For minimum work required to compress and deliver a quantity of air by multistage compression
A. The compression ratio in each stage should be same
B. The intercooling should be perfect
C. The work-done in each stage should be same
D. All of the above
Question 239
Pick up the wrong statement about advantages of multistage compression
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
Question 240
Which is false statement about advantages of multistage compressor in comparison to single stage compressor?
A. Less power requirement
B. Better mechanical balance
C. Less loss of air due to leakage past the cylinder
D. Lower volumetric efficiency
Question 241
In an axial flow compressor, the ratio of pressure in the rotor blades to the pressure rise in the compressor in one stage is known as
A. Work factor
B. Slip factor
C. Degree of reaction
D. Pressure coefficient
Question 242
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
Question 243
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
Question 244
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
Question 245
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 inter-cooler
Question 246
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
Question 247
If the flow of air through the compressor is parallel to its axis, then the compressor is
A. Reciprocating compressor
B. Centrifugal compressor
C. Axial flow compressor
D. Turbo compressor
Question 248
Surging is the phenomenon of
A. Air stream blocking the passage
B. Motion of air at sonic velocity
C. Unsteady, periodic and reversed flow
D. Air stream not able to follow the blade contour
Question 249
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
D. Air stream not able to follow the blade contour
Question 250
A rocket engine uses __________ for the combustion of its fuel.
A. Surrounding air
B. Compressed atmospheric air
C. Its own oxygen
D. None of these
Question 251
Separators in compressor installations are located
A. Before inter-cooler
B. After inter-cooler
C. After receiver
D. Between after-cooler and air receiver
Question 252
Mechanical efficiency of gas turbines as compared to I.C engines is
A. Higher
B. Lower
C. Same
D. None of the above
Question 253
The maximum combustion pressure in gas turbine as compared to I.C. engine is
A. More
B. Less
C. Same
D. Depends on other factors
Question 254
Which of the following fuels can be used in turbojet engines?
A. Liquid hydrogen
B. High speed diesel oil
C. Kerosene
D. Methyl alcohol
Question 255
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
Question 256
Standard air is the air at ________ and relative humidity of 36 percent.
A. 0.1 bar and 20°C
B. 1 bar and 20°C
C. 0.1 bar and 40°C
D. 1 bar and 40°C
Question 257
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
Question 258
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