Energy and Exergy Analyses of the Performance of a Spark Ignition Engine Using Two-Zone Combustion Model

Relying on numerical methods, it is possible to estimate the performance of an engine precisely, and to evaluate the optimization methods of the engine. Almost 30% of the fuel energy is dissipated through the cylinder walls, therefore, accurate calculation of heat transfer rate is necessary to yield reliable results from the simulation model. The thermodynamic model in this paper, that is developed to optimize the performance of a spark ignition engine, utilizes the two-zone combustion model that is suitable for this type of engine. Different models for heat transfer in the engine are used in simulation and compared with available experimental data, and the Hohenberg model is identified as the most precise heat transfer model for spark ignition engine. The results indicate that increase of the compression ratio by 18% leads to almost 2% lower exergy destruction due to engine exhaust and heat transfer to the enegin body, however, the engine power output increases by about 4%. Also, it is concluded that the maximum energy and exergy efficiencies are obtained when combustion takes place 5 degree before top dead center.