1. Ideal Cycles, Air-Standard Assumptions, and The Otto Cycle

2. Thermodynamic Cycles Power Cycles vs Refrigeration Cycles Power Cycles
Gas vs vapor
Closed vs Open
Internal Combustion vs External Combustion

4. Ideal cycles are simplified

5. Be careful how you interpret results from ideal cycles

6. Ideal Cycles More realistic than Carnot cycle.
Internally reversible but not totally.
Idealizations:
No friction
Expansions and compressions – quasi-equilibrium
Heat transfer is negligible

7. Area inside the cycle represents net work out for Ts or Pv
diagrams.

8. Diagrams for a Carnot Cycle

9. Equipment for a Carnot cycle. Changes have to be slow,
with very large heat exchangers, so not practical.

10. Example 8-1 Proof of thermal efficiency of a Carnot cycle
qin and qout are areas under lines
so TH(s2 – s1), etc.

11. Air Standard Assumptions

12. Air Standard Assumptions
Air in closed loop – ideal gas
Internally reversible
Combustion replaced by heat addition
Exhaust replaced by heat rejection
Properties at room temp. – cold air standard assumptions.

13. Nomenclature

15. MEP = mean effective pressure, same amount of work
Compression
ratio?

16. Otto Cycle, ideal for spark ignition engines

17. Two-stroke engine

18. Ts plot of the Otto Cycle

19. Efficiency vs Compression Ratio
Higher ratios produce
autoignition and
knocking

20. Efficiency vs ratio of specific heats
Air
Combustion
mixture

21. Example 8-2 The Ideal Otto Cycle