Numerical Simulation And Study Of Fuelled Ethanol HCCI Engine Combustion

Homogenous charge compression ignition (HCCI) combustion mode is one of focuses of research on internal combustion engines. Engines operated in HCCI mode have the potential to provide better fuel economy and emissions than conventional engines. HCCI engines are being considered as a future alternative for conventional engines. Cost of HCCI engines are low because no high-pressure injection system is required. Emissions of soot are very low because no rich regions exist in the cylinder where soot can form. NOx are also very low when HCCI is used a moderate low speeds and loads because of low combustion temperatures. Unfortunately, CO and HC emissions are relatively high. Operating range of HCCI engines are reduced. HCCI combustion is a process dominated by chemical kinetics of the fuel-air mixture. HCCI engines are difficulty in starting and controlling. With HCCI operation, ignition is controlled solely by in-cylinder conditions.There are three ways to realize HCCI combustion comprised by the method of fueling: port-injection, early in-cylinder injection, and late in-cylinder injection.As reproduced resource or fuel, ethanol has being more and more used in internal combustion engines. During ethanol combustion process, it has two ways to consume ethanol—decomposition reaction and dehydrogenation reaction. At the beginning of reaction, some of ethanol, with third-body providing energy, produced four centered transition states: CH3CH2OH, C2H5OH, C2H4H2O and CH3HCOH2, then decomposed. Further, others of ethanol dehydrogenated with some radicals. Because of three specific H-atom abstraction cites in ethanol, Ethanol dehydrogenation reaction with every radical has three methods.To investigate characteristics of ethanol HCCI engine, this paper created a detailed chemical kinetic HCCI combustion model using mechanisms and thermal data publicized by America Lawrence Livernore National Lab. The model can predict combustion characteristics and histories of species. We used Gear BDF method to solve the stiff difference equations. Gear BDF can control steps automatically to keep enough precision. Results showed good encouragements both step and precision.Used HCCI combustion model, the paper discussed influences of some factors including compression ratio, intake temperature, intake pressure, equivalence ratio engine speed and EGR. The result shows that increasing compression ratio can reduce delay ignition time, promote ignition early, the same to intake temperature. But increasing engine speed or equivalence ratio can prolong delay ignition time. The result also shows that increasing intake pressure can improve Mean Effective Pressure.EGR is consisted mainly of burned gases at high temperature. Its effect on the ignition time and the heat release rate of HCCI combustion should have two aspects. One is thermal effect which is similar to the inlet charge preheat method. The other is chemical effect which is due to the different chemical species EGR contains.Study results of new combustion model show that the compression ratio, intake temperature and EGR have more important influence on HCCI combustion. How to easily control them is the new direction.