Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 12 :: Mechanical Engineering

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Q1. Maximum delivery pressure is a rotary air compressor is of the order of

(A) 6 kg/cm²
(B) 10 kg/cm²
(C) 16 kg/cm²
(D) 25 kg/cm²

Answer: (B) 10 kg/cm²

Q2. The pressure of air at the beginning of the compression stroke is __ the atmospheric pressure.

(A) Equal to
(B) Less than
(C) More than
(D) None of these

Answer: (B) Less than

Q3. Pressure ratio in gas turbines is the ratio of

(A) Compressor pressure ratio
(B) Highest pressure to exhaust pressure
(C) Inlet pressure to exhaust pressure
(D) Pressures across the turbine

Answer: (B) Highest pressure to exhaust pressure

Q4. The efficiency of a jet engine is higher at

(A) Low speeds
(B) High speeds
(C) Low altitudes
(D) High altitudes

Answer: (D) High altitudes

Q5. When the outlet angle from the rotor of a centrifugal compressor is more than 90°, then the blades are said to be

(A) Forward curved
(B) Backward curved
(C) Radial
(D) None of these

Answer: (A) Forward curved

Q6. Water gas is produced by

(A) Carbonisation of coal
(B) Passing steam over incandescent coke
(C) Passing air and a large amount of steam over waste coal at about 65°C
(D) Partial combustion of coal, eke, anthracite coal or charcoal in a mixed air steam blast

Answer: (B) Passing steam over incandescent coke

Q7. In jet engines, paraffin is usually used as the fuel because of its

(A) High calorific value
(B) Ease of atomisation
(C) Low freezing point
(D) Both (A) and (C) above

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

Q8. Work ratio of a gas turbine may be improved by

(A) Decreasing the compression work
(B) Increasing the compression work
(C) Increasing the turbine work
(D) Both (A) and (C) above

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

Q9. In a centrifugal compressor, the flow of air is __ to the axis of compressor.

(A) Parallel
(B) Perpendicular
(C) Inclined
(D) None of these

Answer: (B) Perpendicular

Q10. Which is false statement about air receivers?

(A) These are used to dampen pulsations
(B) These act as reservoir to take care of sudden demands
(C) These increase compressor efficiency
(D) These knock out some oil and moisture

Answer: (C) These increase compressor efficiency

Q11. The efficiency of the vane blower is (where W₁ = Work done due to compression, and W₂ = Work done due to back flow)

(A) W₁/(W₁ + W₂)
(B) W₂/(W₁ + W₂)
(C) (W₁ + W₂)/W₁
(D) (W₁ + W₂)/W₂

Answer: (B) W₂/(W₁ + W₂)

Q12. As the turbine inlet temperature increases, the thermal efficiency of gas turbine for the optimum pressure ratio

(A) Increases
(B) Decreases
(C) Remain same
(D) First increases and then decreases

Answer: (A) Increases

Q13. Pick up the false statement

(A) Gas turbine is a self starting unit
(B) Gas turbine does not require huge quantity of water like steam plant
(C) Exhaust losses in gas turbine are high due to large mass flow rate
(D) Overall efficiency of gas turbine plant is lower than that of a reciprocating engine

Answer: (A) Gas turbine is a self starting unit

Q14. The pressure ratio for an open cycle gas turbine compared to closed cycle gas turbine of same h.p. is

(A) Low
(B) High
(C) Same
(D) Low/high depending on make and type

Answer: (A) Low

Q15. The following is true for an open cycle gas turbine having exhaust heat exchanger. Atmospheric air before entering the compressor is

(A) Heated
(B) Compressed air before entering the combustion chamber is heated
(C) Bled gas from turbine is heated and readmitted for complete expansion
(D) Exhaust gases drive the compressor

Answer: (B) Compressed air before entering the combustion chamber is heated

Q16. In a single stage, single acting reciprocating air compressor without clearance volume, the work-done is maximum during

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

Answer:(B) Isentropic compression

Q17. A rocket engine for the combustion of its fuel

(A) Carries its own oxygen
(B) Uses surrounding air
(C) Uses compressed atmospheric air
(D) Does not require oxygen

Answer:(A) Carries its own oxygen

Q18. Maximum temperature in a gas turbine is of the order of

(A) 700°C
(B) 2000°C
(C) 1500°C
(D) 1000°C

Answer: (A) 700°C

Q19. Aeroplanes employ following type of compressor

(A) Radial flow
(B) Axial flow
(C) Centrifugal
(D) None of the above

Answer:(B) Axial flow

Q20. A rocket engine uses __ for the combustion of its fuel.

(A) Surrounding air
(B) Compressed atmospheric air
(C) Its own oxygen
(D) None of these

Answer: (C) Its own oxygen

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