Mathematical Modeling of Combustion Process in a Spark-Ignition Engine

One-dimensional unsteady analysis of turbulent flame propagation has been used to determine the heat release rate. This model considers the combustion chamber geometry, piston face profile and spark plug location. The chemical kinetic analysis has been used to predict NO emission level as function of time and chamber position. Equilibrium calculation of CO emission level at the end of combustion process has been performed. A computer program has been developed to solve the flame propagation and kinetic equation. The results have been verified by comparing the experimental data such as flame velocity, combustion duration, mass fraction of burned gas versus crank angle, rate of pressure rise and emission levels of NO and CO with those predicted by the model. It was observed that the predicted results agree fairly well with the currently available experimental results at all tested conditions (various rpm and spark timings for 0% EGR and wide open throttle condition) for the whole range of A/F variation from lean to rich limits. A parametric study has been performed to investigate the effects of spark plug locations on combustion duration, flame velocity and emission levels of NO and CO. Based on a parametric study and a comparison of theory, and experiment, it was observed that the flame speeds reach a maximum value as the air-fuel ratio is approximately 10% richer than the stoichiometric ratio and decrease at higher or lower air-fuel ratios. The flame speeds of the engines with concentric spark plug locations are faster than the engines with eccentric spark plug location. Nitrogen oxide levels reach a maximum value as the air-fuel ratio is approximately 10% leaner than the stoichiometric ratio and decrease at higher or lower air-fuel ratios. Carbon monoxide level shows a decreasing trend with increasing air-fuel ratio, leveling off to a minimum value at approximately 0.85 equivalence ratio. It is anticipated that the model will be useful for design studies directed toward improving the efficiency and pollution characteristics of internal combustion engines.