| Summary: In this study, application of exergy analysis to spark ignition engine cycle has been investigated theoretically by using two different thermodynamic cycle model. For this purpose, a thermodynamic cycle model which consist of compression, combustion and expansion processes was developed for spark ignition engines. In the cycle model, induction and exhaust processes were computed with a simple method. Two different cycle models were used in the study. Combustion process is simulated with an empirical correlation as known cosine burn rate formula in first of the cycle models. In the second cycle model, turbulent flame propagation having more realistic hypotheses was used for modeling of combustion period. The second laws of thermodynamics were applied to both of the cycle models to perform exergy analysis. Exergy transfer with heat, exergy transfer with work, irreversibility, thermomechanical exergy, fuel chemical exergy and total exergy were computed in the exergy analysis. In the study, effects of structural parameters such as spark plug position and compression ratio, operational parameters such as equivalence ratio, spark timing, engine speed and residual gas fraction and also, some alternative fuels such as natural gas, Liquefied Petroleum Gas (LPG), methanol and ethanol have been studied. Moreover, the distribution of fuel exergy among the exergy terms was calculated and the first and second law efficiencies were computed to determine optimum values of examined parameters. The obtained results of study showed that design and operational parameters studied and using of alternative fuels affected significantly variation of exergetic terms.
Key Words: SI engine performance, Thermodynamic cycle model, Availability, Irreversibility, The second law analysis, Exergy analysis, The second law efficiency
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