Research On Combustion And Emissions Formation Mechanism Of Ethanol HCCI Engine

With energy shortage, environment pollution, and increasingly stringent emission regulations, the sustainable development of diesel confronts severe challenges. In recently years, many countries pay more attention to the research of clean alternative fuels and new combustion style. Ethanol, which was an oxygenated renewable biofuel, is considered a more promising alternative fuel. Ethanol Homogeneous Charge Compression Ignition (HCCI) engine has been extensively studied because of its good combustion and emission characteristics. But currently there are some problems to be solved, such as the difficulty of ignition control, the narrow range of operating conditions, the highly hydrocarbon (HC) and carbon monoxide (CO) emissions and some unregulated emissions like formaldehyde and acetaldehyde.Firstly this thesis summarizes the research status, existent problems and numerical simulation of ethanol HCCI engines. According to the detailed chemical kinetic mechanism of ethanol proposed by the U.S. Lawrence Livermore Laboratory, this paper analyzes the main approach of ethanol oxidation, and the production and consumption of important intermediate products. Based on the detailed chemical kinetics mechanism, a simplified chemical reaction mechanism is presented by sensitivity analysis and rate of production analysis. Thus a simplified model is constructed, which consists of 33 species and 52 reactions. And then the comparative studies were given between the simplified model and the detailed model. The simulation results show that simplified model and detailed model have good consistency. This simplified model can effectively simulate HCCI engine working operations in a wide range of initial conditions. It also can predict the variational courses of unregulated emissions such as formaldehyde and acetaldehyde, and the CO, NO emission. Thus provides a feasible way for the simulation of the chemical kinetics model coupled with the CFD multidimensional model.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 an ethanol 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 and EGR rate. It provides a theoretical basis for further extending the operation range of HCCI combustion and effectively improving the combustion and emissions performance of ethanol HCCI engine.