Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 10 :: Mechanical Engineering

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Q1. The air-fuel ratio in gas turbines is of the order of

(A) 7: 1
(B) 15: 1
(C) 30: 1
(D) 50: 1.

Answer: (D) 50: 1.

Q2. 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

Answer: (C) It requires cooling water for its operation

Q3. 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

Answer: (B) Gas turbine is capable of rapid start up and loading

Q4. The compression ratio in a gas turbine is of the order of

(A) 3.5 : 1
(B) 5 : 1
(C) 8 : 1
(D) 12 : 1

Answer: (C) 8 : 1

Q5. An air compressor may be controlled by

(A) Throttle control
(B) Clearance control
(C) Blow off control
(D) Any one of the above

Answer: (D) Any one of the above

Q6. The stagnation pressure rise in a centrifugal compressor takes place

(A) In the diffuser only
(B) In the impeller only
(C) In the diffuser and impeller
(D) In the inlet guide vanes only

Answer:(C) In the diffuser and impeller

Q7. If the clearance ratio for a reciprocating air compressor is ‘K’, then its volumetric efficiency is given by

(A) 1 – k + k (p₁/p₂)1/n
(B) 1 + k – k (p₂/p₁)1/n
(C) 1 – k + k (p₁/p₂) n- 1/n
(D) 1 + k – k (p₂/p₁) n-1/n

Answer: (B) 1 + k – k (p₂/p₁)1/n

Q8. In a single stage, single acting reciprocating air compressor, without clearance volume, the work-done is minimum during

(A) Isothermal compression
(B) Isentropic compression
(C) Polytropic compression
(D) None of these

Answer: (A) Isothermal compression

Q9. Air-fuel ratio in a jet engine will be of the order of

(A) 10: 1
(B) 15: 1
(C) 20: 1
(D) 60: 1

Answer: (D) 60: 1

Q10. Euler’s equation can be used for

(A) Radial flow compressors
(B) Axial flow compressors
(C) Pumps
(D) All of these

Answer: (D) All of these

Q11. 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

Answer: (D) To minimize the work of compression

Q12. The combustion efficiency of a gas turbine using perfect combustion chamber is of the order of

(A) 75%
(B) 85%
(C) 90%
(D) 99%

Answer: (D) 99%

Q13. 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

Answer: (B) H.P. compressor is connected to L.P. turbine and L.P. compressor is connected to H.P. turbine

Q14. Reheating in multistage expansion gas turbine results in

(A) High thermal efficiency
(B) Reduction in compressor work
(C) Decrease of heat loss in exhaust
(D) Maximum work output

Answer: (D) Maximum work output

Q15. The minimum work required for a three stage reciprocating air compressor is __ the work required for each stage.

(A) Equal to
(B) Double
(C) Three times
(D) Six times

Answer: (C) Three times

Q11. What will be the volume of air at 327°C if its volume at 27°C is 1.5 m³/ mt?

(A) 3 m³/ mt.
(B) 1.5 m³/ mt.
(C) 18 m³/ mt.
(D) 6 m³/ mt.

Answer: (A) 3 m³/ mt.

Q12. The criterion of the thermodynamic efficiency for rotary compressor is

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

Answer: (A) Isentropic compression

Q13. The ratio of specific weight/h.p. of gas turbine and I.C engines may be typically of the order of

(A) 1: 1
(B) 2: 1
(C) 4: 1
(D) 1: 6

Answer: (D) 1: 6

Q13. In which case the air-fuel ratio is likely to be maximum?

(A) Gas turbine
(B) 4-stroke petrol engine
(C) 4-stroke diesel engine
(D) Multi cylinder engine

Answer: (A) Gas turbine

Q14. Gas turbine works on

(A) Brayton or Atkinson cycle
(B) Carnot cycle
(C) Rankine cycle
(D) Ericsson cycle

Answer: (A) Brayton or Atkinson cycle

Q15. The pressure ratio in gas turbines is of the order of

(A) 2: 1
(B) 4:1
(C) 61: 1
(D) 9: 1

Answer: (C) 61: 1

Q16. 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

Answer: (D) Both pressure ratio and maximum cycle temperature

Q17. A jet engine works on the principle of conservation of

(A) Mass
(B) Energy
(C) Flow
(D) Linear momentum

Answer: (D) Linear momentum

Q18. The main purpose of reheating in gas turbine is to

(A) Increase temperature
(B) Reduce turbine size
(C) Increase power output
(D) Increase speed

Answer: (C) Increase power output

Q19. The air power of the compressor is also known as

(A) Indicated power
(B) Brake power
(C) Frictional power
(D) None of these

Answer: (A) Indicated power

Q20. A 3 m³/min compressor means that it

(A) Compresses 3 m³/min of standard air
(B) Compresses 3 m³/ min of free air
(C) Delivers 3 m³/ min of compressed air
(D) Delivers 3 m³/ min of compressed air at delivery pressure

Answer: (B) Compresses 3 m³/ min of free air

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