Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 8 :: Mechanical Engineering

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Q1. Reheating in a multistage expansion gas turbine __ compressor work.

(A) Has no effect on
(B) Decreases
(C) Increases
(D) None of these

Answer: (B) Decreases

Q2. Maximum work is done in compressing air when the compression is

(A) Isothermal
(B) Adiabatic
(C) Polytropic
(D) None of the above

Answer: (B) Adiabatic

Q3. Clearance volume in actual reciprocating compressors is essential

(A) To accommodate Valves in the cylinder head
(B) To provide cushioning effect
(C) To attain high volumetric efficiency
(D) To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head

Answer: (D) To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head

Q4. Gas turbine as compared to internal combustion engine

(A) Can be driven at a very high speed
(B) Produces uniform torque
(C) Has more efficiency
(D) All of these

Answer: (D) All of these

Q5. Volumetric efficiency of a compressor with clearance volume

(A) Increases with increase in compression ratio
(B) Decreases with increase in compression ratio
(C) In not dependent upon compression ratio
(D) May increase/decrease depending on compressor capacity

Answer: (B) Decreases with increase in compression ratio

Q6. The maximum delivery pressure in a rotary air compressor is

(A) 10 bar
(B) 20 bar
(C) 30 bar
(D) 50 bar

Answer: (A) 10 bar

Q7. Which of the following statement is correct?

(A) The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency
(B) The compression ratio for the compressor is always greater than unity
(C) The compressor capacity is the ratio of work-done per cycle to the stroke volume
(D) During isothermal compression of air, the work-done in a compressor is maximum

Answer: (B) The compression ratio for the compressor is always greater than unity

Q8. The assumption made in two stage compression with inter-cooler is that

(A) There is no pressure drop in the inter-cooler
(B) The compression in both the cylinders is polytropic
(C) The suction and delivery of air takes place at constant pressure
(D) All of the above

Answer: (D) All of the above

Q9. 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

Answer: (C) Axial flow compressor

Q10. A compressor at high altitudes will require __ power.

(A) Same
(B) Less
(C) More
(D) None of these

Answer: (B) Less

Q11. 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

Answer:(D) All of the above

Q12. A jet engine has

(A) No propeller
(B) Propeller in front
(C) Propeller at back
(D) Propeller on the top

Answer: (A) No propeller

Q13. 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

Answer: (B) Axial flow compressors are more stable than centrifugal type compressors but not as efficient

Q14. 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

Answer: (D) First increase, reach maximum and then decrease

Q15. The compressor performance at higher altitude compared to sea level will be

(A) Same
(B) Higher
(C) Lower
(D) Dependent on other factors

Answer: (C) Lower

Q16. 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

Answer: (C) Both (A) and (B) above

Q17. 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

Answer: (D) Lower volumetric efficiency

Q18. Gas turbines for power generation are normally used

(A) To supply base load requirements
(B) To supply peak load requirements
(C) To enable start thermal power plant
(D) In emergency

Answer: (B) To supply peak load requirements

Q19. Fighter bombers use following type of engine

(A) Turbojet
(B) Turbo-propeller
(C) Rocket
(D) Ramjet

Answer: (A) Turbojet

Q20. 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

Answer: (D) Axial flow compressors are bigger in diameter compared to centrifugal type

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