1. TEKNIK PERMESINAN KAPAL II (Minggu – 3) LS 1329 ( 3 SKS) Jurusan Teknik Sistem Perkapalan ITS Surabaya

2. Gas Cycles Carnot Cycle T2 T1 s1 s2 Work W 1 2 3 4 1-2 - ADIABATIC COMPRESSION (ISENTROPIC) 2-3 - HEAT ADDITION (ISOTHERMAL) 3-4 - ADIABATIC EXPANSION (ISENTROPIC) 4-1 - WORK (ISOTHERMAL) Heat Q

4. Carnot Cycle Carnot cycle is the most efficient cycle that can be executed between a heat source and a heat sink. However, isothermal heat transfer is difficult to obtain in reality--requires large heat exchangers and a lot of time.

5. Carnot Cycle Therefore, the very important (reversible) Carnot cycle, composed of two reversible isothermal processes and two reversible adiabatic processes, is never realized as a practical matter. Its real value is as a standard of comparison for all other cycles.

6. Gas cycles have many engineering applications Internal combustion engine  Otto cycle  Diesel cycle Gas turbines  Brayton cycle Refrigeration  Reversed Brayton cycle

7. Some nomenclature before starting internal combustion engine cycles

8. More terminology

9. Terminology Bore = d Stroke = s Displacement volume =DV = Clearance volume = CV Compression ratio = r

10. Mean Effective Pressure Mean Effective Pressure (MEP) is a fictitious pressure, such that if it acted on the piston during the entire power stroke, it would produce the same amount of net work.

11. The net work output of a cycle is equivalent to the product of the mean effect pressure and the displacement volume

12. Real Otto cycle

13. Real and Idealized Cycle

14. Otto Cycle P-V & T-s Diagrams Pressure-VolumeTemperature-Entropy

15. Otto Cycle Derivation Thermal Efficiency:  For a constant volume heat addition (and rejection) process;  Assuming constant specific heat:

16. For an isentropic compression (and expansion) process: where: γ = C p /C v Then, by transposing, Otto Cycle Derivation Leading to

17. Differences between Otto and Carnot cycles

18. The compression ratio (r v ) is a volume ratio and is equal to the expansion ratio in an otto cycle engine. Compression Ratio where Compression ratio is defined as Otto Cycle Derivation

19. Then by substitution, The air standard thermal efficiency of the Otto cycle then becomes: Otto Cycle Derivation

20. Summarizing where andthen Isentropic behavior Otto Cycle Derivation

21. Heat addition (Q) is accomplished through fuel combustion Q = Lower Heat Value (LHV) BTU/lb, kJ/kg Otto Cycle Derivation also

22. Effect of compression ratio on Otto cycle efficiency

23. Sample Problem – 1 The air at the beginning of the compression stroke of an air-standard Otto cycle is at 95 kPa and 22C and the cylinder volume is 5600 cm 3. The compression ratio is 9 and 8.6 kJ are added during the heat addition process. Calculate: (a) the temperature and pressure after the compression and heat addition process (b) the thermal efficiency of the cycle Use cold air cycle assumptions.

24. Draw cycle and label points T 1 = 295 K P 1 = 95 kPa r = V 1 /V 2 = V 4 /V 3 = 9 Q 23 = 8.6 kJ

25. Carry through with solution Calculate mass of air: Compression occurs from 1 to 2: But we need T 3 !

26. Get T 3 with first law: Solve for T 3 :

27. Thermal Efficiency

28. Sample Problem – 2

29. Solution

32. Diesel Cycle P-V & T-s Diagrams

35. Sample Problem – 3

38. Gasoline vs. Diesel Engine