High air-fuel ratio is used in gas turbines
To increase the output
To increase the efficiency
To save fuel
To reduce the exit temperature
Correct Answer :
D. To reduce the exit temperature
Related Questions
The performance of air compressor at high altitudes will be ________ as compared to that at sea level.
Same
Lower
Higher
None of these
It is not possible to use closed gas turbine cycle in aeronautical engines because
It is inefficient
It is bulky
It requires cooling water for its operation
None of the above
The overall thermal efficiency of an ideal gas turbine plant is (where r = Pressure ratio)
r -1
1 - r -1
1 - (1/r) -1/
1 - (1/r) /-1
Which one of the following is the effect of blade shape on performance of a centrifugal compressor?
Backward curved blades has poor efficiency
Backward curved blades lead to stable performance
Forward curved blades has higher efficiency
Forward curved blades produce lower pressure ratio
Only rocket engines can be propelled to space because
They can generate very high thrust
They have high propulsion efficiency
These engines can work on several fuels
They are not air breathing engines
Gas turbine as compared to steam turbine
Requires less space for installation
Has compressor and combustion chamber
Has less efficiency
All of these
In jet engines the products of combustion after passing through the gas turbine are discharged into
Atmosphere
Back to the compressor
Discharge nozzle
Vacuum
If the clearance ratio for a reciprocating air compressor is 'K', then its volumetric efficiency is given by
1 - k + k (p₁/p₂)1/n
1 + k - k (p₂/p₁)1/n
1 - k + k (p₁/p₂) n- 1/n
1 + k - k (p₂/p₁) n-1/n
The degree of reaction of an axial flow turbine is the ratio of isentropic temperature drop in a blade row to the
Adiabatic temperature drop in the stage
Total temperature drop
Total temperature drop in the stage
Total adiabatic temperature drop
The working fluid in a turbine is
In two phases
In three phases
In a single phase
In the form of air and water mixture
In a single stage, single acting reciprocating air compressor, without clearance, the workdone on the air during isentropic compression is ________ the heat required to raise the temperature of air from T₁ to T₂ at a constant pressure.
Equal to
Less than
Greater than
None of these
Reciprocating air compressor is best suited for
Large quantity of air at high pressure
Small quantity of air at high pressure
Small quantity of air at low pressure
Large quantity of air at low pressure
An ideal air compressor cycle with clearance on PV diagram can be represented by following processes
One adiabatic, two isobaric, and one constant volume
Two adiabatic and two isobaric
Two adiabatic, one isobaric and one constant volume
One adiabatic, one isobaric and two constant volumes
Ram compression in turbojet involves
Reduction of speed of incoming air and conversion of part of it into pressure energy
Compression of inlet air
Increasing speed of incoming air
Lost work
The efficiency and work ratio of a gas turbine plant can be increased by
Adding heat exchanger
Injecting water in/around combustion chamber
Reheating the air after partial expansion in the turbine
All of the above
The compressed air may be used
In gas turbine plants
For operating pneumatic drills
In starting and supercharging of I.C. engines
All of the above
High air-fuel ratio is used in gas turbines
To increase the output
To increase the efficiency
To save fuel
To reduce the exit temperature
A simple turbojet engine is basically
A propeller system
Gas turbine engine equipped with a propulsive nozzle and diffuse
Chemical rocket engine
Ramjet engine
The thrust on the rotor in a centrifugal compressor is produced by
Radial component
Axial component
Tangential component
None of the above
Which of the following statement is correct as regard to centrifugal compressors?
The flow of air is parallel to the axis of the compressor
The static pressure of air in the impeller increases in order to provide centripetal force on the air
The impeller rotates at high speeds
The maximum efficiency is higher than multistage axial flow compressors
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
The thermodynamic efficiency of rotary compressor is based on
Isothermal compression
Adiabatic compression
Isentropic compression
Polytropic compression
The minimum work required for a three stage reciprocating air compressor is ________ the work required for each stage.
Equal to
Double
Three times
Six times
Reheating in a multistage expansion gas turbine __________ compressor work.
Has no effect on
Decreases
Increases
None of these
Actual compression curve is
Same as isothermal
Same as adiabatic
Better than isothermal and adiabatic
In between isothermal and adiabatic
The air is delivered ________ in one revolution in case of a three lobbed rotor.
Two times
Three times
Four times
Six times
The gas in cooling chamber of a closed cycle gas turbine is cooled at
Constant volume
Constant temperature
Constant pressure
None of these
Mechanical efficiency of gas turbines as compared to I.C engines is
Higher
Lower
Same
None of the above
For maximum work, the reheating should be done to an intermediate pressure of (Where p₁ = Maximum pressure, and p₂ = Minimum pressure)
(p₁ - p₂)/2
(p₁ + p₂)/2
p₁/p₂
p₁ p₂
Fighter bombers use following type of engine
Turbojet
Turbo-propeller
Rocket
Ramjet