Theoretical And Numerical Study On The Ignition And Combustion Process Of HCCI Engines

With the developing of global economy, the problems of energy crisis and environment pollution become more serious. As the main source of petroleum consumption and emissions to atmosphere, automotive engines have received increased attentions. HCCI (Homogeneous Charge Compression Ignition) is one of the most attractive modes for automotive engines to achieve both high efficiency and low NO_X and particulates emissions. HCCI has grown from an idea to reality in a very short time, and numerical simulation has been a major factor. This thesis is concerned the numerical study of the ignition and combustion process of HCCI engines. The principal aim of this work underling the thesis has been to develop simulation tools that can contribute to understanding and further development of HCCI engines.Firstly, the popular combustion models for HCCI engines have been modified and integrated, and a simulation system including a single-zone model, a multi-zone model, multi-dimensional model and an analytical expression has been developed, which could rapidly bring accurate information for prediction of ignition point, operating range expansion and control of emissions.1. The single-zone model was applied to systemically calculate HCCI combustion and NO_X emissions under different parameters, and the influences of intake temperature, intake pressure, compression ratio, equivalence ratio and engine speed on combustion process of the HCCI engine were discussed.2. A comparative study was carried out to clarify the effect of various sub-models on the prediction capability of the multi-zone model. The influences of the distribution of zones, heat transfer from the wall, mass and heat exchange between zones and boundary layer thickness on HCCI combustion and emissions were discussed based on the experimental data. The results indicate dividing the colder region into more zones can improve the emissions prediction, however, more zones in the hotter region has little effect on the results. The improved Woschni model significantly improves the prediction of heat transfer. It is shown that mass and heat exchange between zones have great influence on the last results, especially that mass exchange model plays an important role in the prediction of CO emission. While the effect of boundary layer thickness is only slight. Therefore, a six zones model with mass exchange was used to study HCCI combustion and emissions with n-heptane as the fuel. The results show that this multi-zone model could predict the HCCI combustion and emissions of...