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Gas Turbines MCQ Mechanical Engineering

Attempt now to check your rank among 44 students! 50 Questions 30 Mins

About Gas Turbines

Following are some of the multiple choice questions on the Gas Turbines with answers that will help the students in developing their knowledge.

Gas Turbines MCQ

1. Gas turbine works on

Brayton or Atkinson cycle
Carnot cycle
Rankine cycle
Ericsson cycle

2. An aftercooler is used to

remove impurities from air
reduce volume of air
cause moisture and oil vapour to drop out
cool the air

3. The overall efficiency of the compressed air system is the

Ratio of shaft output of the air motor to the shaft input to the compressor
Ratio of shaft input to the compressor to the shaft output of air motor
Product of shaft output of air motor and shaft input to the compressor
None of the above

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

Indicated power
Brake power
Frictional power
None of these

5. Which of the following plants is smallest and lightest for generating a given amount of power?

Gas turbine plant
Petrol engine
Diesel engine
Solar plant

6. Which of the following plants is smallest and lightest for generating a given amount of power?

Gas turbine plant
Petrol engine
Diesel engine
Solar plant

7. The degree of reaction in an axial flow compressor is defined as the ratio of static enthalpy rise in the

rotor to static enthalpy rise in the stator
stator to static enthalpy rise in the rotor
rotor to static enthalpy rise in the stage
stator to static enthalpy rise in the stage

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

increases as clearance volume increases
decreases as clearance volume increases
is independent of clearance volume
increases as clearance volume decreases

9. An axial compressor gives optimum performance at high speeds and large volume flows.

Agree
Disagree

10. The increase in pressure in a roots blower is entirely due to back flow of air.

Agree
Disagree

11. If p1, is the pressure of air entering the L.P. cylinder and p2 is the pressure of air leaving the L.P. cylinder (or intercooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where D1 = Dia. of L.P. cylinder, and D2 = Dia. of H.P. cylinder)

D1/D2 = p1p2
D1/D2 = p1/p2
D1/D2 = p2/p1
none of these

12. The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as

compressor efficiency
volumetric efficiency
isothermal efficiency
mechanical efficiency

13. High air-fuel ratio in gas turbines

increases power output
improves thermal efficiency
reduces exhaust temperature
do not damage turbine blades

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

more
less

15. The compression ratio in a gas turbine is

4
1
9
12

16. The actual volume of air delivered by a compressor, When reduced to the normal temperature and pressure conditions is called compressor capacity.

Yes
No

17. When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is __________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.

equal to
less than
more than

18. Intercooling in gas turbines

decreases net output but increases thermal efficiency
increases net output but decreases thermal efficiency
decreases net output and thermal efficiency both
increases net output and thermal efficiency both

19. A closed cycle gas turbine gives __________ efficiency as compared to an open cycle gas turbine.

same
lower
higher

20. A large clearance Volume in a reciprocating compressor results in

reduced volume flow rate
increased volume flow rate
lower suction pressure
lower delivery pressure

21. In a centrifugal compressor, an increase in speed at a given pressure ratio causes

increase in flow
decrease in flow
increase in efficiency
increase in flow and decrease in efficiency

22. A rotary compressor is driven by an

electric motor
engine
either (a) or (b)
none of these

23. Workdone by a two-stage reciprocating air compressor per cycle is equal to the workdone in LP. cylinder and H.P. cylinder.

True
False

24. Rotary compressors are used for delivering

small quantities of air at high pressures
large quantities of air at high pressures
small quantities of air at low pressures
large quantities of air at low pressures

25. The efficiency of a jet engine is higher at

low speeds
high speeds
low altitudes
high altitudes

26. The type of rotary compressor used in gas turbines, is of

centrifugal type
axial flow type
radial flow type
none of these

27. In the aircraft propellers

the propulsive matter is ejected from within the propelled body
the propulsive matter is caused to flow around the propelled body
its functioning does not depend upon the presence of air
none of the above

28. 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

p2 = (p1 + p3)/2
p2 = p1.p3
P2 = Pa x p3/p1
p2 = pa p3/p1

29. The inlet pressure is always __________ the discharge pressure.

equal to
less than
more than

30. The clearance volume in the compressor is kept minimum because it effects on volumetric efficiency.

Correct
Incorrect

31. The ratio of workdone per cycle to the stroke volume of the compressor is known as

compressor capacity
compression ratio
compressor efficiency
mean effective pressure

32. Intercooling in multi-stage compressors is done

to cool the air during compression
to cool the air at delivery
to enable compression in two stages
to minimise the work of compression

33. The capacity of a compressor is expressed in

kg/m2
kg/m3
m3/min
m3/kg

34. The increase in pressure in a vane blower takes place first due to compression and then due to back flow of air.

Correct
Incorrect

35. An open cycle gas turbine works on the same cycle as that of a closed cycle gas turbine.

Yes
No

36. The total heat rejected in a reciprocating air compressor is equal to the sum of the heat rejected during polytropic compression per kg of air and heat rejected in the intercooler per kg of air.

True
False

37. The rotary compressors are suitable for large discharge of air at low pressure.

True
False

38. The volumetric efficiency for reciprocating air compressors is about

10 to 40%
40 to 60%
60 to 70%
70 to 90%

39. A rocket works with maximum overall efficiency when air-craft velocity is __________ the jet velocity.

equal to
one-half
double

40. The compressed air may be used

in gas turbine plants
for operating pneumatic drills
in starting and supercharging of I. engines
all of the above

41. In a four stage compressor, if the pressure at the first and third stage are 1 bar and 16 bar, then the delivery pressure at the fourth stage will be

1 bar
16 bar
64 bar
256 bar

42. The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is

Pressure drop across the valves
Superheating in compressor
Clearance volume and leakages
All of these

43. In a jet engine, the air-fuel ratio is

30:1
40:1
50:1
60:1

44. Free air is the air at

Atmospheric conditions at any specific location
20°C and 1 kg/cm² and relative humidity of 36%
0°C and standard atmospheric conditions
15°C and 1 kg/cm²

45. Standard air is the air at

Atmospheric conditions at any specific location
20°C and 1 kg/cm² and relative humidity 36%
0°C and standard atmospheric conditions
15°C and 1 kg/cm²

46. The work-done on a compressor will be minimum if air is taken from

The atmosphere
A source at 0° C
A source of low temperature air
A source of high temperature air

47. In a double acting compressor, the air is compressed

In one cylinder
In two cylinders
In a single cylinder on both sides of the piston
In two cylinders on both sides of the piston

48. The maximum delivery pressure in a rotary air compressor is

10 bar
20 bar
30 bar
50 bar

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

34%
50%
60%
72%

50. The type of rotary compressor used in aeroplanes, is of

Centrifugal type
Axial flow type
Radial flow type
None of these

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