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Mechanical Engineering
Compressors, Gas Turbines And Jet Engines
Quiz 8
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Q.1
A simple turbojet engine is basically
A propeller system
Gas turbine engine equipped with a propulsive nozzle and diffuse
Chemical rocket engine
Ramjet engine
Q.2
The efficiency of a jet engine is higher at
Low speeds
High speeds
Low altitudes
High altitudes
Q.3
The degree of reaction in an axial flow compressor is defined as the ratio of static enthalpy rise in the
Rotor to static enthalpy rise in the stator
Stator to static enthalpy rise in the rotor
Rotor to static enthalpy rise in the stage
Stator to static enthalpy rise in the stage
Q.4
The performance of air compressor at high altitudes will be ________ as compared to that at sea level.
Same
Lower
Higher
None of these
Q.5
Maximum work is done in compressing air when the compression is
Isothermal
Adiabatic
Polytropic
None of the above
Q.6
The following property is most important for material used for gas turbine blade
Toughness
Fatigue
Creep
Corrosion resistance
Q.7
The main purpose of reheating in gas turbine is to
Increase temperature
Reduce turbine size
Increase power output
Increase speed
Q.8
In the cross compounding of the gas turbine plant
H.P. compressor is connected to H.P. turbine and L.P. compressor to L.P. turbine
H.P. compressor is connected to L.P. turbine and L.P. compressor is connected to H.P. turbine
Both the arrangements can be employed
All are connected in series
Q.9
The advantage of multistage compression over single stage compression is
Lower power consumption per unit of air delivered
Higher volumetric efficiency
Decreased discharge temperature
All of the above
Q.10
1 m of air at atmospheric condition weighs approximately
0.5 kg
1.0 kg
1.3 kg
2.2 kg
Q.11
The clearance volume of the air compressor is kept minimum because
It allows maximum compression to be achieved
It greatly affects volumetric efficiency
It results in minimum work
It permits isothermal compression
Q.12
Which is false statement about multistage compression?
Power consumption per unit of air delivered is low
Volumetric efficiency is high
It is best suited for compression ratios around 7:1
The moisture in air is condensed in the inter-cooler
Q.13
The following is true for an open cycle gas turbine having exhaust heat exchanger. Atmospheric air before entering the compressor is
Heated
Compressed air before entering the combustion chamber is heated
Bled gas from turbine is heated and readmitted for complete expansion
Exhaust gases drive the compressor
Q.14
If the flow of air through the compressor is parallel to its axis, then the compressor is
Reciprocating compressor
Centrifugal compressor
Axial flow compressor
Turbo compressor
Q.15
Surging is the phenomenon of
Air stream blocking the passage
Motion of air at sonic velocity
Unsteady, periodic and reversed flow
Air stream not able to follow the blade contour
Q.16
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
Work factor
Slip factor
Degree of reaction
Pressure coefficient
Q.17
A rocket engine for the combustion of its fuel
Carries its own oxygen
Uses surrounding air
Uses compressed atmospheric air
Does not require oxygen
Q.18
The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as
Compressor efficiency
Volumetric efficiency
Isothermal efficiency
Mechanical efficiency
Q.19
The pressure of air at the beginning of the compression stroke is ________ the atmospheric pressure.
Equal to
Less than
More than
None of these
Q.20
More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than
2 kg/cm²
6 kg/cm²
10 kg/cm²
14.7 kg/cm²
Q.21
In a centrifugal compressor, an increase in speed at a given pressure ratio causes
Increase in flow
Decrease in flow
Increase in efficiency
Increase in flow and decrease in efficiency
Q.22
A closed gas turbine in which fuel is burnt directly in the air is not possible because of
Paucity of O2
Increasing gas temperature
High specific volume
High friction losses
Q.23
For minimum work required to compress and deliver a quantity of air by multistage compression
The compression ratio in each stage should be same
The intercooling should be perfect
The work-done in each stage should be same
All of the above
Q.24
Pick up the wrong statement about advantages of multistage compression
Better lubrication is possible advantages of multistage
More loss of air due to leakage past the cylinder
Mechanical balance is better
Air can be cooled perfectly in between
Q.25
Which is false statement about advantages of multistage compressor in comparison to single stage compressor?
Less power requirement
Better mechanical balance
Less loss of air due to leakage past the cylinder
Lower volumetric efficiency
Q.26
The air-fuel ratio in gas turbines is of the order of
7: 1
15: 1
30: 1
50: 1.
Q.27
Maximum delivery pressure is a rotary air compressor is of the order of
6 kg/cm²
10 kg/cm²
16 kg/cm²
25 kg/cm²
Q.28
Maximum temperature in a gas turbine is of the order of
700°C
2000°C
1500°C
1000°C
Q.29
The maximum compression ratio in an actual single stage axial flow compressor is of the order of
1 : 1.2
1 : 2
1 : 5
1 : 10
Q.30
The type of rotary compressor used in gas turbines, is of
Centrifugal type
Axial flow type
Radial flow type
None of these
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