In this paper a three dimensional model of a spark ignition engine is presented using KIVA-3V code to investigate the combustion process of engine and gain a better understanding of what happens during this stage. The Whole engine cycle is simulated and the validity of the model is examined by experimental result of in-cylinder bulk pressure. the effect of ignition timing, spark plug location on the engine performance and pollutants of this engine has been investigated .The numerical results

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... w that Relocating the spark plug near to the exhaust valves in order of taking advantage of higher temperature does not have the desired results. Using lean excessive air results in decreasing advancing the ignition results in an increase in the maximum bulk pressure and power of engine. Due to increase in maximum temperature of the combustion chamber the amount of NOx rises, too.