Research On Combustion And Emissions Formation Mechanism Of LPG HCCI Engine

Now. every country is studying actively to develop clean and efficient auto alternative fuels. Because of the increasingly strict emission standards due to environmental concerns and desire for more efficient conversion from energy to mechanical power. Liquefied petroleum gas (LPG) engine is widely researched because of its good fuel economy and very low emissions of NOx and soot. Homogeneous Charge Compression Ignition (HCCI) engines are being paid much attention and widely investigated due to their potential of high thermal efficiency and very low emissions of NOx and particulate matter (PM).Since detailed chemical kinetic models can increase the computational burden so greatly that they are beyond the current ordinary PC capabilities, a new reduced chemical kinetic model was developed in this paper. Firstly this thesis summarizes the research status, existent problems and numerical simulation of LPG engines. A detailed chemical kinetic mechanism has been build up according to the data that proposed by the U.S. Lawrence Livermore Laboratory and related documents. Based on the chemical reaction kinetics soft CHEMKIN, the thermodynamic combustion sub-model of the engine fuelled with LPG is build up for the simulation of the liquefied petroleum gas Homogeneous Charge Compression Ignition. Base on the studying above, a reduced model of liquefied petroleum gas has been developed by sensitivity analysis and reaction path analysis of intermediate species. The new reduced mechanism consists of37species and98elementary reactions and it has been validated under engine condition. The results show that it gives predictions similar to the detailed model in the ignition timing, in-cylinder temperature and pressure, NO and CO emission. Furthermore, the reduced mechanism can be used to simulate LPG combustion in good agreement with the detailed mechanism.In addition, this paper builds a three-dimensional model. With this reduced model coupling with the CFD software Fluent, then it calculates the combustion and emission characteristics of a liquefied petroleum gas HCCI engine. We analyze the combustion process and formation mechanism of regulated and unregulated emissions. And discuss the influence of different initial conditions on the combustion processes and emissions, such as equivalence ratio, EGR rate and compression ratio. It provides a theoretical basis for further extending the operation range of HCCI combustion and effectively improving the combustion and emissions performance of liquefied petroleum gas HCCI engine.