### Multiple Choice Questions and Answers (MCQs) on Compressors, Gas Turbines and Jet Engines

01. If the flow of air through the compressor is perpendicular to its axis, then it is a

(A) Reciprocating compressor
(B) Centrifugal compressor
(C) Axial flow compressor
(D) Turbo compressor

02. Gas turbines use following type of air compressor

(A) Centrifugal type
(B) Reciprocating type
(C) Lobe type
(D) Axial flow type

03. The gas in cooling chamber of a closed cycle gas turbine is cooled at

(A) Constant volume
(B) Constant temperature
(C) Constant pressure
(D) None of these

04. The maximum combustion pressure in gas turbine as compared to I.C. engine is

(A) More
(B) Less
(C) Same
(D) Depends on other factors

05. In a closed cycle gas turbine, the air is compressed

(A) Isothermally
(B) Polytropically
(C) Isentropically
(D) None of these

06. The closed cycle in gas turbines

(A) Provides greater flexibility
(B) Provides lesser flexibility
(C) In never used
(D) Is used when gas is to be burnt

07. The overall thermal efficiency of an ideal gas turbine plant is (where r = Pressure ratio)

(A) r ɣ-1
(B) 1 – r ɣ-1
(C) 1 – (1/r) ɣ-1/ɣ
(D) 1 – (1/r) ɣ/ɣ-1

08. Pick up the correct statement

(A) Large gas turbines use radial inflow turbines
(B) Gas turbines have their blades similar to steam turbine
(C) Gas turbine’s blade will appear as impulse section at the hub and as a reaction section at tip
(D) Gas turbines use both air and liquid cooling

09. The degree of reaction is usually kept ________ for all types of axial flow compressors.

(A) 0.2
(B) 0.3
(C) 0.4
(D) 0.5

10. Ram compression in turbojet involves

(A) Reduction of speed of incoming air and conversion of part of it into pressure energy
(B) Compression of inlet air
(C) Increasing speed of incoming air
(D) Lost work

11. A compressor mostly used for supercharging of I.C. engines is

(B) Axial flow compressor
(C) Roots blower
(D) Reciprocating compressor

12. In jet engines, for the efficient production of large power, fuel is burnt in an atmosphere of

(A) Vacuum
(B) Atmospheric air
(C) Compressed air
(D) Oxygen alone

13. The workdone on a compressor will be minimum if air is taken from

(A) The atmosphere
(B) A source at 0°C
(C) A source of low temperature air
(D) A source of high temperature air

14. In the aircraft propellers

(A) The propulsive matter is caused to flow around the propelled body
(B) Propulsive matter is ejected from within the propelled body
(C) Its functioning does not depend on presence of air
(D) All of the above

15. In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into

(A) Atmosphere
(B) Vacuum
(C) Discharge nozzle
(D) Back to the compressor

16. To avoid moisture troubles, the branch connections from compressed air lines should be taken from

(A) Top side of main
(B) Bottom side of main
(C) Left side of main
(D) Right side of main

17. In an axial flow compressor, the ratio of pressure in the rotor blades to the pressure rise in the compressor in one stage is known as

(A) Work factor
(B) Slip factor
(C) Degree of reaction
(D) Pressure coefficient

18. To avoid moisture troubles, the compressed air main line should

(A) Rise gradually towards the point of use
(B) Drop gradually towards the point of use
(C) Be laid vertically
(D) Be laid exactly horizontally

19. The volumetric efficiency of a compressor

(A) Increases with decrease in compression ratio
(B) Decreases with decrease in compression ratio
(C) Increases with increase in compression ratio
(D) Decreases with increase in compression ratio

20. The efficiency and work ratio of a gas turbine plant can be increased by

(B) Injecting water in/around combustion chamber
(C) Reheating the air after partial expansion in the turbine
(D) All of the above

21. The capacity of compressor will be highest when its intake temperature is

(A) Lowest
(B) Highest
(C) Anything
(D) Atmospheric

22. The volume of air sucked by the compressor during its suction stroke is called

(A) Free air delivery
(B) Compressor capacity
(C) Swept volume
(D) None of these

23. Which is false statement about multistage compression?

(A) Power consumption per unit of air delivered is low
(B) Volumetric efficiency is high
(C) It is best suited for compression ratios around 7:1
(D) The moisture in air is condensed in the intercooler

24. Standard air is the air at ________ and relative humidity of 36 percent.

(A) 0.1 bar and 20°C
(B) 1 bar and 20°C
(C) 0.1 bar and 40°C
(D) 1 bar and 40°C