Numerical Simulation of the Gas Flow Accompanied by Pressure Wave Propagation and Diffusion Phenomena in Internal Combustion Engines

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It is important to reduce the numerical error, that is, false diffusion error in order to improve the simulation accuracy of unsteady gas flows in internal combustion engines. The results obtained through the investigation of various methods are as follows :1. By using the CIP method with high accuracy because its false diffusion is very small, the diffusion process of injected gas due to vortex motion has been made clear. Furthermore, the diffusion process of the mixture of fuel gas and air in a spark ignition engine has been numerically analyzed by the CIP method, and the process of stratified mixture formation has been shown. By incorporating fuel spray models into the calculation program to numerically analyze the process of mixture formation in a port-fuel-injection engine, the behavior of fuel droplets and the distribution of fuel vapor concentration have been predicted.2. In predicting the engine performances, it is necessary to evaluate various gas flows in exhaust systems. The method based on characteristics has been developed for the gas flow in a tapered pipe and also for the gas flow with the steep change of temperature. Applying this method to the prediction program, the optimization problem of engine systems has been discussed. The results shows that the program is useful in developing the engine systems.3. In three-dimensional analysis of gas flow including pressure wave, a method has been investigated for predicting the effects of the configurations of silencers on both the pressure losses and the acoustic characteristics in the silencer. By comparing the calculated pressure losses to the experimental ones, it has been confirmed that the method enables one to predict the trend of change of the pressure losses to the dimensions of silencer.