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Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 02
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Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 02
1
In jet propulsion power unit, the inlet duct of diverging shape is used in order to
A
Collect more air
B
Convert kinetic energy of air into pressure energy
C
Provide robust structure
D
Beautify the shape
2
Volumetric efficiency of a compressor without clearance volume
A
Increases with increase in compression ratio
B
Decreases with increase in compression ratio
C
Is not dependent upon compression ratio
D
May increase/decrease depending on compressor capacity
3
The mean effective pressure of the compressor is the
A
ctual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B
Volume of air delivered by the compressor
C
Volume of air sucked by the compressor during its suction stroke
D
None of the above
4
An ideal air compressor cycle without clearance on P-V diagram can be represented by following processes
A
One adiabatic, two isobaric, and one constant volume
B
Two adiabatic and two isobaric
C
Two adiabatic, one isobaric and one constant volume
D
One adiabatic, one isobaric and two constant volumes
5
The thrust of a jet propulsion power unit can be increased by
A
Injecting water into the compressor
B
Burning fuel after gas turbine
C
Injecting ammonia into the combustion chamber
D
All of the above
6
Maximum work is done in compressing air when the compression is
A
Isothermal
B
Adiabatic
C
Polytropic
D
None of these
7
A rotary compressor is driven by an
A
Electric motor
B
Engine
C
Either (A) or (B)
D
None of these
8
Isothermal compression though most efficient, but is not practicable because
A
It requires very big cylinder
B
It does not increase pressure much
C
It is impossible in practice
D
Compressor has to run at very slow speed to achieve it
9
Gas turbine as compared to steam turbine
A
equires less space for installation
B
Has compressor and combustion chamber
C
Has less efficiency
D
All of the these
10
The following property is most important for material used for gas turbine blade
A
Toughness
B
Fatigue
C
Creep
D
Corrosion resistance
11
The ratio of work done per cycle to the swept volume in case of compressor is called
A
Compression index
B
Compression ratio
C
Compressor efficiency
D
Mean effective pressure
12
Intercooling in gas turbines
A
Decreases net output but increases thermal efficiency
B
Increases net output but decreases thermal efficiency
C
Decreases net output and thermal efficiency both
D
Increases net output and thermal efficiency both
13
The efficiency of jet engine is
A
Lower at low speed
B
Higher at high altitudes
C
Same at all altitudes
D
Higher at high speed
14
Compression efficiency is compared against
A
Ideal compression
B
Adiabatic compression
C
Isentropic compression
D
Isothermal compression
15
High air-fuel ratio in gas turbines
A
Increases power output
B
Improves thermal efficiency
C
Reduces exhaust temperature
D
Do not damage turbine blades
16
An ideal air compressor cycle with clearance on P-V diagram can be represented by following processes
A
One adiabatic, two isobaric, and one constant volume
B
Two adiabatic and two isobaric
C
Two adiabatic, one isobaric and one constant volume
D
One adiabatic, one isobaric and two constant volumes
17
In gas turbines, high thermal efficiency is obtained in
A
Closed cycle
B
Open cycle
C
Both of the above
D
Closed/open depending on other considerations
18
Ratio of indicated H.P. and brake H.P. is known as
A
Mechanical efficiency
B
Volumetric efficiency
C
Isothermal efficiency
D
Adiabatic efficiency
19
The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as
A
Compressor efficiency
B
Volumetric efficiency
C
Isothermal efficiency
D
Mechanical efficiency
20
Clearance volume in actual reciprocating compressors is essential
A
To accommodate Valves in the cylinder head
B
To provide cushioning effect
C
To attain high volumetric efficiency
D
To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head
21
In a turbo jet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded in
A
Exit nozzle, which is a constant volume process
B
Exit nozzle, which is essentially an isentropic process
C
Turbine blades, which is a constant volume process
D
Turbine blades, which is essentially an isentropic process
22
1 m of air at atmospheric condition weighs approximately
A
0.5 kg
B
1.0 kg
C
1.3 kg
D
2.2 kg
23
The overall efficiency of the compressed air system is the
A
Ratio of shaft output of the air motor to the shaft input to the compressor
B
Ratio of shaft input to the compressor to the shaft output of air motor
C
Product of shaft output of air motor and shaft input to the compressor
D
None of these
24
Adiabatic compression is one in which
A
Temperature during compression remains constant
B
No heat leaves or enters the compressor cylinder during compression
C
Temperature rise follows a linear relationship
D
Work done is maximum
25
A machine used to raise the pressure of air is called
A
Gas turbine
B
C engine
C
Compressor
D
Air motor
26
The capacity of a compressor is 5 m/min refers to
A
Standard air
B
Free air
C
Compressed air
D
Compressed air at delivery pressure
27
The process, which causes the air to enter the impeller blades of a centrifugal compressor at ________ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.
A
Reduced
B
Increased
C
Zero
D
None of these
28
The overall isothermal efficiency of compressor is defined as the ratio of
A
Isothermal h.p. to the BHP of motor
B
Isothermal h.p. to adiabatic h.p.
C
Power to drive compressor to isothermal h.p.
D
Work to compress air isothermally to work for actual compression
29
In a centrifugal compressor, the ratio of the ________ to the blade velocity is called slip factor.
A
Inlet whirl velocity
B
Outlet whirl velocity
C
Inlet velocity of flow
D
Outlet velocity of flow
30
The most efficient method of compressing air is to compress it
A
Isothermally
B
Adiabatically
C
Isentropically
D
Isochronically
31
The performance of air compressor at high altitudes will be ________ as compared to that at sea level.
A
Same
B
Lower
C
Higher
D
None of these
32
The pressure and temperature conditions of air at the suction of compressor are
A
Atmospheric
B
Slightly more than atmospheric
C
Slightly less than atmospheric
D
Pressure slightly less than atmospheric and temperature slightly more than atmospheric
33
Which of the following statement is correct as regard to centrifugal compressors?
A
The flow of air is parallel to the axis of the compressor
B
The static pressure of air in the impeller increases in order to provide centripetal force on the air
C
The impeller rotates at high speeds
D
The maximum efficiency is higher than multistage axial flow compressors
34
Isothermal compression efficiency can be attained by running the compressor
A
(A) At very high speed
B
At very slow speed
C
At average speed
D
At zero speed
35
. Gas turbine as compared to internal combustion engine
A
Can be driven at a very high speed
B
Produces uniform torque
C
Has more efficiency
D
All of these
36
Rotary compressors are used for delivering
A
Small quantities of air at high pressures
B
Large quantities of air at high pressures
C
Small quantities of air at low pressures
D
Large quantities of air at low pressures
37
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
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
39
The advantage of multistage compression over single stage compression is
A
Lower power consumption per unit of air delivered
B
Higher volumetric efficiency
C
Decreased discharge temperature
D
All of the above
40
Rotary compressors are used for delivering
A
Small quantities of air at high pressures
B
Large quantities of air at high pressures
C
Small quantities of air at low pressures
D
Large quantities of air at low pressures
41
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
42
Only rocket engines can be propelled to space because
A
They can generate very high thrust
B
They have high propulsion efficiency
C
These engines can work on several fuels
D
They are not air breathing engines
43
Only rocket engines can be propelled to space because
A
They can generate very high thrust
B
They have high propulsion efficiency
C
These engines can work on several fuels
D
They are not air breathing engines
44
The advantage of multistage compression over single stage compression is
A
Lower power consumption per unit of air delivered
B
Higher volumetric efficiency
C
Decreased discharge temperature
D
All of the above
45
Reheating in a gas turbine
A
Increases the thermal efficiency
B
Increases the compressor work
C
Increases the turbine work
D
Decreases the thermal efficiency
46
Pick up the wrong statement about advantages of multistage compression
A
Better lubrication is possible advantages of multistage (B) (D)
B
More loss of air due to leakage past the cylinder
C
Mechanical balance is better
D
Air can be cooled perfectly in between
47
For perfect intercooling in a three stage compressor
A
p₂/p₠= p₃/p₂ = p₄/p₃
B
p₃/p₠= p₄/p₂
C
p₠p₂ = p₃ p₄
D
p₠p₃ = p₂ p₄
48
The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called
A
Slip factor
B
Velocity factor
C
Velocity coefficient
D
None of the above
49
When the temperature of air leaving the inter-cooler, in a two stage compression with inter-cooler, is ________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.
A
Equal to
B
Less than
C
More than
D
None of these
50
Losses in a centrifugal compressor are due to
A
Inlet losses
B
Impeller channel losses
C
Diffuser losses
D
All of the above
51
he axial flow compressor is preferred in aircraft gas turbines because of
A
Low frontal area
B
Higher thrust
C
High pressure rise
D
None of these
52
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%
53
If pâ‚, is the pressure of air entering the L.P. cylinder and pâ‚‚ is the pressure of air leaving the L.P. cylinder (or inter-cooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where Dâ‚ = Dia. of L.P. cylinder, and Dâ‚‚ = Dia. of H.P. cylinder)
A
Dâ‚/Dâ‚‚ = pâ‚ pâ‚‚
B
Dâ‚/Dâ‚‚ = pâ‚/pâ‚‚
C
Dâ‚/Dâ‚‚ = pâ‚‚/pâ‚
D
None of these
54
The indicated work per unit mass of air delivered is
A
Directly proportional to clearance volume
B
Greatly affected by clearance volume
C
Not affected by clearance volume
D
Inversely proportional to clearance volume
55
Which of the following statement is correct?
A
The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency
B
The compression ratio for the compressor is always greater than unity
C
The compressor capacity is the ratio of work-done per cycle to the stroke volume
D
During isothermal compression of air, the work-done in a compressor is maximum
56
n nâ‚ and nâ‚‚ are the indices of compression for the first and second stage of compression, then the ratio of work-done on the first and second stages (Wâ‚/Wâ‚‚) with perfect intercooling is given by
A
Wâ‚/Wâ‚‚ = nâ‚‚(nâ‚ - 1)/nâ‚(nâ‚‚ - 1)
B
Wâ‚/Wâ‚‚ = nâ‚(nâ‚‚ - 1)/nâ‚‚(nâ‚ - 1)
C
Wâ‚/Wâ‚‚ = nâ‚/nâ‚‚
D
Wâ‚/Wâ‚‚ = nâ‚‚/nâ‚
57
For supplying intermittent small quantity of air at high pressure, following compressor is best suited
A
Centrifugal
B
Reciprocating
C
Axial
D
Screw
58
The absolute pressure of air at the outlet of a compressor is called
A
Back pressure
B
Critical pressure
C
Discharge pressure
D
None of these
59
For minimum work in multistage compression, assuming same index of compression in all stages
A
Work done in first stage should be more
B
Work done in subsequent stages should increase
C
Work done in subsequent stages should decrease
D
Work done in all stages should be equal
60
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
61
For a two stage compressor, if index of compression for higher stage is greater than index of compression for lower stage, then the optimum pressure as compared to ideal case will
A
Increase
B
Decrease
C
Remain unaffected
D
Other factors control it
62
Which one of the following is the effect of blade shape on performance of a centrifugal compressor?
A
Backward curved blades has poor efficiency
B
Backward curved blades lead to stable performance
C
Forward curved blades has higher efficiency
D
Forward curved blades produce lower pressure ratio
63
Diffuser in a compressor is used to
A
Increase velocity
B
Make the flow streamline
C
Convert pressure energy into kinetic energy
D
Convert kinetic energy into pressure energy
64
A closed cycle gas turbine consists of a
A
Compressor
B
Heating chamber
C
Cooling chamber
D
All of these
65
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
66
The mass of gas turbine per kW developed is about ________ as that of an I.C. engine.
A
Same
B
One-half
C
One fourth
D
One sixth
67
The thermodynamic efficiency of rotary compressor is based on
A
Isothermal compression
B
Adiabatic compression
C
Isentropic compression
D
Polytropic compression
68
The type of rotary compressor used in aeroplanes, is of
A
Centrifugal type
B
Axial flow type
C
Radial flow type
D
None of these
69
Phenomenon of choking in compressor means
A
No flow of air
B
Fixed mass flow rate regardless of pressure ratio
C
Reducing mass flow rate with increase in pressure ratio
D
Increased inclination of chord with air steam
70
The assumption made in two stage compression with inter-cooler is that
A
There is no pressure drop in the inter-cooler
B
The compression in both the cylinders is polytropic
C
The suction and delivery of air takes place at constant pressure
D
All of the above
71
Propulsive efficiency is defined as ratio of
A
Thrust power and fuel energy
B
Engine output and propulsive power
C
Propulsive power and fuel input
D
Thrust power and propulsive power
72
In jet engines, paraffin is usually used as the fuel because of its
A
High calorific value
B
Ease of atomisation
C
Low freezing point
D
Both (A) and (C) above
73
A rocket engine for the combustion of its fuel
A
Carries its own oxygen
B
Uses surrounding air
C
Uses compressed atmospheric air
D
Does not require oxygen
74
A rocket works with maximum overall efficiency when air craft velocity is equal to the
A
Jet velocity
B
Twice the jet velocity
C
Half the jet velocity
D
Average of the jet velocity
75
Propulsion efficiency of the following order is obtained in practice
A
34%
B
50%
C
60%
D
72%
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