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

Ideal Cycles, Air-Standard Assumptions, and The Otto Cycle. Thermodynamic Cycles. Power Cycles vs Refrigeration Cycles Power Cycles Gas vs vapor Closed vs Open Internal Combustion vs External Combustion. Ideal cycles are simplified. Be careful how you interpret results from ideal cycles.

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

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  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

  3. Ideal cycles are simplified

  4. Be careful how you interpret results from ideal cycles

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

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

  7. Diagrams for a Carnot Cycle

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

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

  10. Air Standard Assumptions

  11. 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.

  12. Nomenclature

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

  14. Otto Cycle, ideal for spark ignition engines

  15. Two-stroke engine

  16. Ts plot of the Otto Cycle

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

  18. Efficiency vs ratio of specific heats He Air Combustion mixture

  19. Example 8-2 The Ideal Otto Cycle

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