A search for maximum efficiency and NO x reduction through spark-ignition engine design optimization at λ =1

Abstract

In this study a multizone model of spark-ignition engine combustion is validated and used to predict the thermal efficiency and NO _x emissions of the engine. The model is validated against an engine map obtained from an extensive series of experiments. An optimizing algorithm based on particle swarm concepts is applied to the model to find a trade-off between efficiency and NO _x emissions using a predefined cost function. Optimization is performed for three cases, each of which progressively includes more variables for optimization. A further constrained optimization case is performed with constant values of several of the variables set at the average values found in the three prior cases. These variables are the ones that change over a small domain. The results show the potential improvement in efficiency while achieving remarkably low NO _x emissions. They emphasize the importance of exhaust gas recirculation (EGR) at high compression ratio and high loads when the maximum in-cylinder pressures are very high. They also suggest some strategies for valve timings that use internal EGR (residual gas) and move towards different compression and expansion ratios (Atkinson cycle).

Keywords

maximum thermal efficiency spark-ignition engine optimizing algorithm exhaust gas recirculation PSO algorithm residual fraction

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