The efficiency of a jet engine is higher at
Low speeds
High speeds
Low altitudes
High altitudes
Correct Answer :
D. High altitudes
Related Questions
The air entry velocity m a rocket as compared to aircraft is
Same
More
Less
Zero
The indicated work per unit mass of air delivered is
Directly proportional to clearance volume
Greatly affected by clearance volume
Not affected by clearance volume
Inversely proportional to clearance volume
Which of the following statement is correct relating to rocket engines?
The combustion chamber in a rocket engine is directly analogous to the reservoir of a supersonic wind tunnel
The stagnation conditions exist at the combustion chamber
The exit velocities of exhaust gases are much higher than those in jet engine
All of the above
The combustion efficiency of a gas turbine using perfect combustion chamber is of the order of
75 %
85 %
90 %
99 %
The ratio of the net work obtained from the gas turbine plant to the turbine work is known as
Compression ratio
Work ratio
Pressure ratio
None of these
Aeroplanes employ following type of compressor
Radial flow
Axial flow
Centrifugal
None of the above
A rocket engine uses ________ for the combustion of its fuel.
Surrounding air
Compressed atmospheric air
Its own oxygen
None of these
Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is
Higher
Lower
Equal
Cant be compared
The compressor efficiency is the
Isothermal H.P/indicated H.R
Isothermal H.P./shaft H.R
Total output/air input
Compression work/motor input
The ratio of isentropic work to Eulers work is known as
Compressor efficiency
Isentropic efficiency
Euler's efficiency
Pressure coefficient
Pick up the wrong statement
Pulsejet requires no ambient air for propulsion
Ramjet engine has no turbine
Turbine drives compressor in a Turbojet
Bypass turbojet engine increases the thrust without adversely affecting, the propulsive efficiency and fuel economy
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
Vi = Vo
Vt > Vo
U < Vo
V = Uo
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
A compressor at high altitude will draw
More power
Less power
Same power
More/less power depending on other factors
In jet propulsion power unit, the inlet duct of diverging shape is used in order to
Collect more air
Convert kinetic energy of air into pressure energy
Provide robust structure
Beautify the shape
The volume of air delivered in a medium capacity air compressor per unit time is
0.1 to 1.2 m³/s
0.15 to 5 m³/s
Above 5 m³/s
None of these
The pressure ratio of an ideal vaned compressor with increase in mass flow rate
Increases
Decreases
Remain constant
First decreases and then increases
Pressure ratio in gas turbines is the ratio of
Compressor pressure ratio
Highest pressure to exhaust pressure
Inlet pressure to exhaust pressure
Pressures across the turbine
The air power of the compressor is also known as
Indicated power
Brake power
Frictional power
None of these
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
Ratio of indicated H.P. and brake H.P. is known as
Mechanical efficiency
Volumetric efficiency
Isothermal efficiency
Adiabatic efficiency
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 minimum work required for a three stage reciprocating air compressor is ________ the work required for each stage.
Equal to
Double
Three times
Six times
The compression ratio for the compressor is always __________ unity.
Equal to
Less than
More than
None of these
Diffuser in a compressor is used to
Increase velocity
Make the flow streamline
Convert pressure energy into kinetic energy
Convert kinetic energy into pressure energy
Gas turbine cycle with regenerator
Increases thermal efficiency
Allows high compression ratio
Decreases heat loss is exhaust
Allows operation at very high altitudes
Volumetric efficiency of a compressor with clearance volume
Increases with increase in compression ratio
Decreases with increase in compression ratio
In not dependent upon compression ratio
May increase/decrease depending on compressor capacity
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
In jet engines the products of combustion after passing through the gas turbine are discharged into
Atmosphere
Back to the compressor
Discharge nozzle
Vacuum
In a high pressure compressor, the delivery pressure is
1 to 5 bar
5 to 8 bar
8 to 10 bar
10 to 15 bar