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

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

## 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

## 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
(D) None of these

## 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

(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

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

## 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

## 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

## 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

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

## Q19. Aeroplanes employ following type of compressor

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