Gas Turbine and Gas power Cycle | Interview Question and Answers

Gas Turbine and Gas power Cycle | Interview viva, oral Question and Answers

1. Define cycle.

It is defined as a series of state changes such that the final state is identical with the initial state.

2. Define the term compression ratio.

Compression ratio is the ratio between total cylinder volume to clearance volume. It is denoted by the letter ‘r’

3. What is the range of compression ratio for SI and diesel engine?

For petrol of SI engine 6 to 8
For diesel engine 12 to 18

4. Which cycle is more efficient for the same compression ratio and heat input, Otto cycle or Diesel cycle?

Otto cycle is more efficient than diesel cycle

5. Write the expression for efficiency of the Otto cycle?

Efficiency n =1 – 1/(rc)^γ-1

6. The efficiency of the diesel cycle approaches the Otto cycle efficiency when the cut off ratio is______

Ans: Reduced

7. The speed of a four stroke I.C. engine is 1500rpm. What will be the speed of the cam shaft?

750m.

8.All the four operations in two stroke engine are performed in ________ number of revolution of crank shaft.

Ans: One

9. All the four operations in four stroke engine are performed in _______ number of revolution of crank shaft.

Ans: Two

10. In otto cycle the compression ratio is _______ to expansion ratio.

Ans: Equal

11. In diesel engine, the compression ratio is __________ than expansion ratio?

Ans: Greater

12. What is meant by cutoff ratio?

Cutoff ratio is defined as the ratio of volume after the heat addition to before the heat addition. It is denoted by the letter ‘ρ’

13. What are the assumptions made for air standard cycle.

a. Air is the working substance.
b. Throughout the cycle, air behaves as a perfect gas and obeys all the gas laws.
c. No chemical reaction takes place in the cylinder
d. Both expansion and compression are strictly isentropic
e. The values of specific heats of the air remain constant throughout the cycle.

14. Define Mean effective pressure of an I.C. engine.

Mean effective pressure is defined as the constant pressure acting on the piston during the working stroke. It is also defined as the ratio of work done to the stroke volume or piston displacement volume.

15. What is the other name given to Otto cycle?

Constant volume cycle.

16. What is an air standard efficiency?

It is defined as the ratio of work done by the cycle to the heat supplied to the cycle.

Efficiency ή = Work done / Heat supplied

17. What will be the effect of compression ratio on efficiency of the diesel cycle?

Efficiency increases with the increase in compression ratio and vice – versa.

18. What will be the effect of cut off ratio on efficiency of the diesel cycle?

Efficiency decreases with the increase of cut off ratio and vice – versa.

19. Define: Specific fuel consumption.

SFC is defined as the amount of fuel consumed per brake power hour of work.

20. What is the difference between Otto and Diesel cycle.

Otto Cycle& Diesel Cycle
1. Otto cycle consist of two adiabatic and two constant volume process.
1. It consists of two adiabatic, one constant volume and one constant pressure processes.
2. Compression ratio is equal to expansion ratio
2. Compression ratio is greater than expansion ratio.
3. Heat addition takes place at constant volume.
3. Heat addition takes place at constant pressure
4. Compression ratio is less. It is varies from 6 to 8.

21. The thermal efficiency of a two stroke cycle engine is _______ than the four stroke cycle engine.

Lesser

22. What is meant by calorific value of a fuel?

Calorific value of a fuel is defined as the amount of heat liberated by the compete combustion of unit quantity of a fuel.

23. The efficiency of the Dual cycle is ___ Greater ____ than the diesel cycle and __Lesser____ than the otto cycle for the same

compression ratio.

24. What are the factors influencing of the Dual cycle?

a. Compression ratio
b. Cut off ratio
c. Pressure ratio
d. Heat supplied at constant volume and constant pressure.

25. The Brayton cycle is mainly used in _______

Gas turbine power plant.

26. Mention the various processes in diesel cycle and dual cycle.

Diesel cycle: Isentropic compression and expansion, constant volume heat rejection and constant pressure heat addition.
Dual cycle: Isentropic compression and expansion, partially heat supplied at constant volume and remaining at constant pressure and constant volume heat rejection.

27. The diesel engine draws the mixture of diesel and air during suction stroke (True / False)

Ans: False

28. What is the effect of air standard efficiency of Diesel cycle with compression ratio and cut off ratio?

Efficiency increases with the increase in compression ratio and vice-versa. The efficiency decreases with the increase in cut off ratio and vice-versa.

29. Name the various gas power cycles

Carnot cycle, Otto cycle, Diesel cycle, Dual cycle, Brayton cycle, Atkinson cycle, Stirling cycle

30. Define mean effective pressure as applied to gas power cycles.

Mean effective pressure is defined as the constant pressure acting on the piston during

31. Compare the Diesel and Brayton cycles Diesel cycle & Brayton cycle

1. It consist of two isentropic, one constant 1. It consist of two isentropic, one constant volume and one constant pressure processes pressure processes
2. Heat is rejected at constant volume 2. Heat is rejected at constant pressure
3. Used in Diesel engines 3. Used in gas turbines

32. Why Brayton cycle is used in gas turbine?

Inside the turbine the gas is continuously flowing in the processes are flow processes. Since all the processes involved in Brayton cycle is flow process, it has been used as the cycle for gas turbine.

33. What is meant by closed cycle gas turbine?

In closed cycle gas turbine, the same working fluid is recirculated again and again.

34. What is meant by open cycle gas turbine?

In open cycle gas turbine, the exhaust gas form turbine is exhausted to the atmosphere and fresh air is taken in compressor for every cycle.

35. Gas turbine is working on ———– cycle

Brayton or Joules cycle.

36. How can we increase the efficiency of the gas turbine?

By providing inter cooler, re-heater along with heat exchanges.

37. What is the function of intercooler in gas turbines? Where it is placed?

The intercooler is placed between L.P. and H.P. compressors. It is used to cool the gas coming from L.P. compressor to its original temperature.

38. Why re-heater is necessary in gas turbine? What are its effects?

The expansion process is very often performed in two separate turbine stages. The re-heater is placed between the H.P. and L.P. turbines to increase the enthalpy of the exhaust gas coming from H.P. turbine.

Effects:
1. Turbine output is increased for the same compression ratio
2. Thermal efficiency is less.

39. What is the function of regenerator in gas turbine?

The main function of heat regenerator is to exchange the heat from exhaust gas to the-compressed air for preheating before combustion chamber. It increases fuel economy and thermal efficiency.