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Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 03
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Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 03
1
With the decrease in compression ratio, the volumetric efficiency
A
Does not change
B
Increases
C
Decreases
D
First decrease and then increase
2
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
3
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
4
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
5
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
6
Axial flow compressor resembles
A
Centrifugal pump
B
Reciprocating pump
C
Turbine
D
Sliding vane compressor
7
The efficiency of roots blower ________ with the increase in pressure ratio.
A
Decreases
B
Increases
C
Does not change
D
None of these
8
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
9
The maximum temperature in a gas turbine is
A
200°C
B
500°C
C
700°C
D
1000°C
10
Actual compression curve is
A
Same as isothermal
B
Same as adiabatic
C
Better than isothermal and adiabatic
D
In between isothermal and adiabatic
11
In a centrifugal compressor, an increase in speed at a given pressure ratio causes
A
Increase in flow
B
Decrease in flow
C
Increase in efficiency
D
Increase in flow and decrease in efficiency
12
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
13
For maximum work, the reheating should be done to an intermediate pressure of (Where pâ‚ = Maximum pressure, and pâ‚‚ = Minimum pressure)
A
(pâ‚ - pâ‚‚)/2
B
(pâ‚ + pâ‚‚)/2
C
pâ‚/pâ‚‚
D
pâ‚ pâ‚‚
14
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
15
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
16
A compressor at high altitudes will require ________ power.
A
Same
B
Less
C
More
D
None of these
17
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
18
The compression ratio for the compressor is always _________ unity.
A
Equal to
B
Less than
C
More than
D
None of these
19
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
20
Euler's equation can be used for
A
Radial flow compressors
B
Axial flow compressors
C
Pumps
D
All of the above
21
The ratio of the indicated power to the shaft power or brake power of the motor or engine required to drive the compressor, is called
A
Compressor efficiency
B
Volumetric efficiency
C
Isothermal efficiency
D
Mechanical efficiency
22
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
23
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
24
The efficiency of a jet engine is higher at
A
Low speeds
B
High speeds
C
Low altitudes
D
High altitudes
25
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
26
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) (D)
A
One stroke
B
Two strokes
C
Three strokes
D
Four strokes
27
Open cycle gas turbine works on (A)
A
Brayton or Atkinson cycle
B
Rankine cycle
C
Carnot cycle
D
Ericsson cycle
28
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
29
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 these
30
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
31
The degree of reaction in an axial flow compressor is defined as the ratio of static enthalpy rise in the
A
Rotor to static enthalpy rise in the stator
B
Stator to static enthalpy rise in the rotor
C
Rotor to static enthalpy rise in the stage
D
Stator to static enthalpy rise in the stage
32
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
33
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
34
A large clearance volume in a reciprocating compressor results in
A
Increased volume flow rate
B
Reduced volume flow rate
C
Lower suction pressure
D
Lower delivery pressure
35
The air-fuel ratio in gas turbines is of the order of
A
7: 1
B
15: 1
C
30: 1
D
50: 1.
36
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
37
The pressure ratio in gas turbines is of the order of
A
2: 1
B
4:1
C
61: 1
D
9: 1
38
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
39
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
40
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
41
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
42
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
43
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
44
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
45
The inlet pressure is always ________ the discharge pressure.
A
Equal to
B
Less than
C
More than
D
None of these
46
The inlet pressure is always ________ the discharge pressure.
A
Equal to
B
Less than
C
More than
D
None of these
47
The inlet pressure is always ________ the discharge pressure.
A
Equal to
B
Less than
C
More than
D
None of these
48
The inlet pressure is always ________ the discharge pressure.
A
Equal to
B
Less than
C
More than
D
None of these
49
The inlet pressure is always ________ the discharge pressure.
A
Equal to
B
Less than
C
More than
D
None of these
50
The inlet pressure is always ________ the discharge pressure.
A
Equal to
B
Less than
C
More than
D
None of these
51
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
52
The volume of air delivered by the compressor is called
A
Free air delivery
B
Compressor capacity
C
Swept volume
D
None of these
53
A jet engine has
A
No propeller
B
Propeller in front
C
Propeller at back
D
Propeller on the top
54
The material commonly used for air craft gas turbine is
A
Stainless steel
B
High alloy steel
C
Duralumin
D
Timken, Haste alloys
55
The material commonly used for air craft gas turbine is
A
Stainless steel
B
High alloy steel
C
Duralumin
D
Timken, Haste alloys
56
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
57
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
58
The combustion efficiency of a gas turbine using perfect combustion chamber is of the order of
A
75%
B
85%
C
90%
D
99%
59
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
60
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
61
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
62
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
63
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
64
Water is injected in gas turbine cycle to
A
Control temperature
B
Control output of turbine
C
Control fire hazards
D
Increase efficiency
65
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.
66
The volumetric efficiency for reciprocating air compressors is about
A
10 to 40%
B
40 to 60%
C
60 to 70%
D
70 to 90%
67
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
68
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
69
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
70
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
71
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
72
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
73
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
74
A jet engine works on the principle of conservation of
A
Mass
B
Energy
C
Flow
D
Linear momentum
75
Which of the following fuels can be used in turbojet engines?
A
Liquid hydrogen
B
High speed diesel oil
C
Kerosene
D
Methyl alcohol
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