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A Numerical Simulation Study on Improving the Thermal Efficiency of a Spark Ignited Engine --- Part 1: Modeling of a Spark Ignited Engine Combustion to Predict Engine Performance Considering Flame Propagation, Knock, and Combustion Chamber Wall ---
Abstract:
The first objective of this work is to develop a numerical simulation model of the spark ignited (SI) engine combustion, taking into account knock avoidance and heat transfer between in-cylinder gas and combustion chamber wall. Secondly, the model was utilized to investigate the potential of reducing heat losses by applying a heat insulation coating to the combustion chamber wall, thereby improving engine thermal efficiency. A reduction in heat losses is related to important operating factors of improving SI engine thermal efficiency. However, reducing heat losses tends to accompany increased combustion chamber wall temperatures, resulting in the onset of knock in SI engines. Thus, the numerical model was intended to make it possible to investigate the interaction of the heat losses and knock occurrence. The present paper consists of Part 1 and 2. Part 1 deals with the description of the numerical model and the fundamental characteristics of instantaneous temperature swings in the combustion chamber wall.
The numerical model is developed by utilizing GT-POWER combined with three sub-models; a non-dimensional two-zone combustion model, an autoignition model in the unburned gas and an instantaneous heat transfer model in the combustion chamber wall. The combustion model considers the flame speeds affected by the in-cylinder conditions. The Shell model was utilized to predict autoignition. The heat transfer model in the combustion chamber wall calculates the instantaneous one-dimensional thermal conductivity, and further predicts wall surface and inside temperatures. The fluctuation range of calculated temperature swings is reasonably similar to measured data obtained in previous studies.