Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 13 :: Mechanical Engineering

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Q1. Surging is the phenomenon of

(A) Air stream blocking the passage
(B) Motion of air at sonic velocity
(C) Unsteady, periodic and reversed flow
(D) Air stream not able to follow the blade contour

Answer: (C) Unsteady, periodic and reversed flow


Q2. There is a certain pressure ratio (optimum) for a gas turbine at which its thermal efficiency is maximum. With increase in turbine temperature, the value of pressure ratio for the peak efficiency would

(A) Remain same
(B) Decrease
(C) Increase
(D) None of the above

Answer: (C) Increase


Q3. The pressure and temperature conditions of air at the suction of compressor are

(A) Atmospheric
(B) Slightly more than atmospheric
(C) Slightly less than atmospheric
(D) Pressure slightly less than atmospheric and temperature slightly more than atmospheric

Answer: (D) Pressure slightly less than atmospheric and temperature slightly more than atmospheric


Q4. In a single acting reciprocating compressor, the suction, compression and delivery of air takes place in __ of the piston.

(A) One stroke
(B) Two strokes
(C) Three strokes
(D) Four strokes

Answer: (B) Two strokes


Q5. Gas turbine blades are given a rake

(A) Equal to zero
(B) In the direction of motion of blades
(C) Opposite to the direction of motion of blades
(D) Depending on the velocity

Answer: (B) In the direction of motion of blades


Q6. Water is injected in gas turbine cycle to

(A) Control temperature
(B) Control output of turbine
(C) Control fire hazards
(D) Increase efficiency

Answer: (B) Control output of turbine


Q7. A rocket works with maximum overall efficiency when air craft velocity is equal to the

(A) Jet velocity
(B) Twice the jet velocity
(C) Half the jet velocity
(D) Average of the jet velocity

Answer: (C) Half the jet velocity


Q8. In air breathing jet engine, the jet is formed by expanding

(A) Highly heated atmospheric air
(B) Solids
(C) Liquid
(D) Plasma

Answer: (A) Highly heated atmospheric air


Q9. In a reciprocating air compressor, the compression work per kg of air

(A) Increases as clearance volume increases
(B) Decreases as clearance volume increases
(C) Is independent of clearance volume
(D) Increases as clearance volume decreases

Answer: (C) Is independent of clearance volume


Q10. The volumetric efficiency of a compressor falls roughly as follows for every 100 m increase in elevation

(A) 0.1%
(B) 0.5%
(C) 1.0%
(D) 5%

Answer: (C) 1.0%


Q11. Rotary compressors are suitable for

(A) Large discharge at high pressure
(B) Low discharge at high pressure
(C) Large discharge at low pressure
(D) Low discharge at low pressure

Answer: (C) Large discharge at low pressure


Q12. A closed cycle gas turbine gives __ efficiency as compared to an open cycle gas turbine.

(A) Same
(B) Lower
(C) Higher
(D) None of these

Answer: (C) Higher


Q13. Open cycle gas turbine works on

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

Answer: (A) Brayton or Atkinson cycle


Q14. The inlet pressure is always __ the discharge pressure.

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

Answer: (B) Less than


Q15. A gas turbine used in air craft should have

(A) High h.p. and low weight
(B) Low weight and small frontal area
(C) Small frontal area and high h.p.
(D) High speed and high h.p.

Answer: (B) Low weight and small frontal area


Q16. Propulsion efficiency of the following order is obtained in practice

(A) 34%
(B) 50%
(C) 60%
(D) 72%

Answer: (C) 60%


Q17. Ramjet engine

(A) Is self operating at zero flight speed
(B) Is not self operating at zero flight speed
(C) Requires no air for its operation
(D) Produces a jet consisting of plasma

Answer: (B) Is not self operating at zero flight speed


Q18. The clearance volume of the air compressor is kept minimum because

(A) It allows maximum compression to be achieved
(B) It greatly affects volumetric efficiency
(C) It results in minimum work
(D) It permits isothermal compression

Answer: (B) It greatly affects volumetric efficiency


Q19. For a two stage reciprocating compressor, compression from p₁ to p₃ is with perfect intercooling and no pressure losses. If compression in both the cylinders follows the same polytropic process and the atmospheric pressure is pa, then the intermediate pressure p₂ is given by

(A) p₂ = (p₁ + p₃)/2
(B) p₂ = p₁. p₃
(C) P₂ = Pa × p₃/p₁
(D) p₂ = Pa p₃/p₁

Answer: (B) p₂ = p₁. p₃


Q20. For perfect intercooling in a two stage compressor

(A) p₂/p₁ = p₃/p₂
(B) p₁/p₃ = p₂/p₁
(C) p₁ = p3
(D) p₁ = p₂ p3

Answer: (A) p₂/p₁ = p₃/p₂


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