1. Engineering Thermodynamics ME-103By
Prof. S.K.Shukla
Department of Mechanical Engineering
Indian Institute of Technology (Banaras Hindu University)
Varanasi

2. GAS POWER CYCLE

3. Internal Combustion Engine
I C Engines
Spark Ignition
Engine
Compression
Ignition
These engines are Petrol Engines and they work on Otto Cycle
These engines are Diesel Engines and they work on Diesel Cycle

4. Basic Components of IC Engine

5. Basic Definitions
The piston inside the cylinder reciprocates between two fixed extreme positions called top – dead centre (TDC) and bottom – dead centre (BDC).
Displacement Volume:
It is the volume swept by the piston when it moves between TDC and BDC.
This is also called as swept volume or stroke volume.
Clearance Volume:
It is the minimum volume formed in the cylinder when the piston is at the TDC.

6. Basic Definitions

7. Indicator Diagram
This indicates the power developed due to combustion inside the cylinder.
This is nothing but the P-v diagram.

8. IC Engine Power Cycles
The sequence of events in an IC engine power cycle are,
Induction of charge.
Compression of charge.
Ignition of charge.
Expansion of the burning gases.
Exhaust of the burnt gases.

9. Petrol Engine
Petrol Engine
Four – Stroke
Two - Stroke

10. Petrol Engine (Four Stroke)

11. Petrol Engine (Two Stroke)
In two – stroke engine, valves are replaced by ports.
There are three ports:
Inlet port
Exhaust port
Transfer port

12. Petrol Engine (Two Stroke)
In two – stroke engine, valves are replaced by ports.
There are three ports:
Inlet port
Exhaust port
Transfer port

13. Events of Petrol Engine (2 Stroke)

14. Processes in Otto Cycle
The processes in Otto cycle are:
(1 – 2) Isentropic Compression
(2 – 3) Constant volume heat addition.
(3 – 4) Isentropic Expansion.
(4 – 1) Constant volume heat rejection.

15. Efficiency of Otto Cycle

16. Efficiency of Otto Cycle

17. Diesel Cycle
Petrol Engine has a Carburetor and a spark plug whereas, a Diesel engine has fuel injector to spray diesel.

18. Diesel Cycle

19. Processes in Diesel Cycle
The processes in Diesel cycle are:
(1 – 2) Isentropic Compression
(2 – 3) Constant pressure heat addition.
(3 – 4) Isentropic Expansion.
(4 – 1) Constant volume heat rejection.

20. Efficiency of Diesel Cycle

21. Dual Cycle

22. Processes in Dual Cycle
The processes in Dual cycle are:
(1 – 2) Isentropic Compression
(2 – 3) Constant volume heat addition.
(3 – 4) Constant Pressure heat addition
(4 – 5) Isentropic Expansion.
(5 – 1) Constant volume heat rejection.

23. Efficiency of Diesel Cycle

24. Efficiency of Diesel Cycle

25. Mean Effective Pressure of Diesel Cycle

26. Comparison of Otto, Diesel and Dual Cycles
The performance of three cycles are compared on the basis of the following important variables.
Compression ratio
Maximum pressure
Heat addition
Net work output

27. Comparison of Otto, Diesel and Dual Cycles
Same Compression ratio and Heat input

28. Comparison of Otto, Diesel and Dual Cycles
Same maximum pressure and Heat input

29. Comparison of Otto, Diesel and Dual Cycles
Same maximum pressure and Temperature

30. Gas Power Cycles

31. Assumptions
In gas power cycles, the working fluid is gas. The following assumptions are made for convenience:
The working fluid is air which continuously circulates in a closed loop.
Air behaves as an ideal gas all through.
All the processes that make up the cycle are internally reversible.
The combustion process is equivalent to the heat addition stage from an external source.
The exhaust process is equivalent to the heat rejection process that restores the working fluid to the initial stage.

32. Simple Gas Turbine

33. Simple Gas Turbine Gas turbine works on Brayton (Joule) cycle.
The various processes are,
(1 – 2) Isentropic Compression
(2 – 3) Reversible constant pressure heating
(3 – 4) Adiabatic Expansion
(4 – 1) Reversible constant pressure cooling

34. Air Standard Brayton Cycle
P – v Diagram (for open and closed cycle

35. Air Standard Brayton Cycle
T - s Diagram

36. Efficiency of Brayton Cycle