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Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 04
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Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 04
1
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
2
The air entry velocity m a rocket as compared to aircraft is
A
Same
B
More
C
Less
D
Zero
3
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
4
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
5
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
6
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
7
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
8
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
9
The main purpose of reheating in gas turbine is to
A
Increase temperature
B
Reduce turbine size
C
Increase power output
D
Increase speed
10
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
11
Work ratio of a gas turbine plant is ratio of
A
Net work output and work done by turbine (B) (D)
B
Net work output and heat supplied
C
Work done by turbine and heat supplied
D
Work done by turbine and net work output
12
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
13
Maximum temperature in a gas turbine is of the order of
A
700°C
B
2000°C
C
1500°C
D
1000°C
14
In air breathing jet engine, the jet is formed by expanding
A
Highly heated atmospheric air
B
Solids
C
Liquid
D
Plasma
15
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
16
For speed above 3000 km/hour, it is more advantageous to use
A
Turbojet engine
B
Ramjet engine
C
Propellers
D
Rockets
17
A simple turbojet engine is basically
A
propeller system
B
Gas turbine engine equipped with a propulsive nozzle and diffuse
C
Chemical rocket engine
D
Ramjet engine
18
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
19
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
20
The compressor performance at higher altitude compared to sea level will be
A
Same
B
Higher
C
Lower
D
Dependent on other factors
21
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
22
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
23
An air compressor may be controlled by
A
Throttle control
B
Clearance control
C
Blow off control
D
Any one of the above
24
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
25
The air power of the compressor is also known as
A
Indicated power
B
Brake powe
C
Frictional power
D
None of these
26
The compressor capacity with decrease in suction temperature
A
Increases
B
Decreases
C
Remain unaffected
D
May increase or decrease depending on compressor capacity
27
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
28
In a centrifugal compressor, the flow of air is ________ to the axis of compressor.
A
Parallel
B
Perpendicular
C
Inclined
D
None of these
29
Aeroplanes employ following type of compressor
A
Radial flow
B
Axial flow
C
Centrifugal
D
None of these
30
In a reciprocating air compressor, the compression work per kg of air
A
Increases as clearance volume increases
B
Decreases as clearance volume increases
C
Is independent of clearance volume
D
Increases as clearance volume decreases
31
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
32
Free air is the air at
A
Atmospheric conditions at any specific location
B
0°C and standard atmospheric conditions
C
15°C and 1 kg/cm²
D
20°C and 1 kg/cm² and relative humidity of 36%
33
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 Tâ‚ to Tâ‚‚ at a constant pressure.
A
Equal to
B
Less tha
C
Greater than
D
None of these
34
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
35
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
36
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
37
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
38
The stagnation pressure rise in a centrifugal compressor takes place
A
In the diffuser only
B
In the impeller only
C
In the diffuser and impeller
D
In the inlet guide vanes only
39
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.
40
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
41
Euler's equation is applicable for
A
Centrifugal compressor
B
Axial compressor
C
Pumps
D
All of the above
42
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
43
Which is false statement about air receivers?
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
44
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
45
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%
46
For a two stage reciprocating compressor, compression from p₠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 = (p₠+ p₃)/2
B
pâ‚‚ = pâ‚. p₃
C
Pâ‚‚ = Pa × p₃/pâ‚
D
pâ‚‚ = Pa p₃/pâ‚
47
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
48
The type of rotary compressor used in gas turbines, is of
A
Centrifugal type
B
Axial flow type
C
Radial flow type
D
None of these
49
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
50
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
51
In a jet propulsion
A
The propulsive matter is ejected from within the propelled body
B
The propulsive matter is caused to flow around the propelled body
C
Its functioning does not depend upon presence of air
D
None of these
52
The ratio of isentropic work to Euler work is known as
A
Pressure coefficient
B
Work coefficient
C
Polytropic reaction
D
Slip factor
53
Inter-cooling 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
54
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
55
Fighter bombers use following type of engine
A
Turbojet
B
Turbo-propeller
C
Rocket
D
Ramjet
56
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
57
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
58
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
59
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
60
In turbo fan engine, the jet velocity as compared to turbojet engine is
A
Less
B
More
C
Same
D
May be less or more depending upon speed
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