Gas turbines are a type of internal combustion engine that extract energy from a stream of compressed air and use it to do work. The work is usually used to drive an electric generator or a compressor. The air is compressed, combined with fuel, and then ignited. This causes the gas turbine to turn, which in turn powers an electric generator.
Types of gas turbines
- The open cycle gas turbine (OCGT) is the most common type of gas turbine. It is used in power generation and oil & gas applications.
- The closed cycle gas turbine (CCGT) is a newer type of gas turbine that is more efficient than the OCGT. It is used in power generation and industrial applications.
- The aircraft gas turbine (AGT) is the type of gas turbine used in jet engines.
- Gas turbines are classified based on their operating principle:
- The impulse type Gas Turbine uses the momentum of a high velocity jet of fluid to turn the rotor.
- The reaction type Gas Turbine uses the propelling action of the fluid to turn the rotor.
Wrapping Up
Gas turbines are used in a variety of applications, including power generation, jet engines, and marine propulsion.
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
2. An aftercooler is used to
3. The overall efficiency of the compressed air system is the
4. The air power of the compressor is also known as
5. Which of the following plants is smallest and lightest for generating a given amount of power?
6. The degree of reaction in an axial flow compressor is defined as the ratio of static enthalpy rise in the
7. In a reciprocating air compressor, the compression work per kg of air
8. An axial compressor gives optimum performance at high speeds and large volume flows.
9. The increase in pressure in a roots blower is entirely due to back flow of air.
10. 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)
11. The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as
12. High air-fuel ratio in gas turbines
13. The maximum combustion pressure in gas turbine is __________ as compared to I.C. engine.
14. The compression ratio in a gas turbine is
15. The actual volume of air delivered by a compressor, When reduced to the normal temperature and pressure conditions is called compressor capacity.
16. 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.
17. Intercooling in gas turbines
18. A closed cycle gas turbine gives __________ efficiency as compared to an open cycle gas turbine.
19. A large clearance Volume in a reciprocating compressor results in
20. In a centrifugal compressor, an increase in speed at a given pressure ratio causes
21. A rotary compressor is driven by an
22. Workdone by a two-stage reciprocating air compressor per cycle is equal to the workdone in LP. cylinder and H.P. cylinder.
23. Rotary compressors are used for delivering
24. The efficiency of a jet engine is higher at
25. The type of rotary compressor used in gas turbines, is of
26. In the aircraft propellers
27. 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
28. The inlet pressure is always __________ the discharge pressure.
29. The clearance volume in the compressor is kept minimum because it effects on volumetric efficiency.
30. The ratio of workdone per cycle to the stroke volume of the compressor is known as
31. Intercooling in multi-stage compressors is done
32. The capacity of a compressor is expressed in
33. The increase in pressure in a vane blower takes place first due to compression and then due to back flow of air.
34. An open cycle gas turbine works on the same cycle as that of a closed cycle gas turbine.
35. 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.
36. The rotary compressors are suitable for large discharge of air at low pressure.
37. The volumetric efficiency for reciprocating air compressors is about
38. A rocket works with maximum overall efficiency when air-craft velocity is __________ the jet velocity.
39. The compressed air may be used
40. 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
41. The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is
42. In a jet engine, the air-fuel ratio is
43. Free air is the air at
44. Standard air is the air at
45. The work-done on a compressor will be minimum if air is taken from
46. In a double acting compressor, the air is compressed
47. The maximum delivery pressure in a rotary air compressor is
48. Propulsion efficiency of the following order is obtained in practice
49. The type of rotary compressor used in aeroplanes, is of
50. Isothermal compression though most efficient, but is not practicable because
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