Numerical And Experimental Study On Direct Liquid Injection And Combustion In CI Engine Fueled With Liquefied Alternative Fuels

With the energy crisis of the world being more intensive, many countries pay more attention to the research of substitute fuels of engine. Based on a lot of references of substitute fuels, this paper summarizes current researches of substitute fuels and focuses on introducing the chemical and physical characteristics of Dimethyl Ether (DME) and Liquefied Petroleum Gas (LPG), and briefly presents research methods of numerical simulation. In accordance with the chemical and physical characteristics of DME and LPG, based on the references and previous experience, the author designed and established the experiment sets of DME DI engine and LPG/Diesel double-fuels DI engine, worked on the DI engine fueled with DME and 15% mass ratio LPG/Diesel double-fuels DI engine, and got the results of the performance of combustion and exhaust emissions. Compared with the engine fueled with diesel, the engines fueled with DME and 15%LPG/Diesel are able to reach the same power outputs and better performance of exhaust emissions of NOx and Soot. The author also designed and established the experiments sets of High Speed Photography on LPG spray in constant volume chamber to investigate the development of LPG spray, the results of experiment is reasonable according to the theoretical analysis. By calculating with self-development simulation program of Fortran, this paper completed a numerical simulation of working process of DME DI engine by zero-dimensional model, and the result of calculation agreed well with the experiment one. The result of this working verified that zero-dimensional model is valuable to simulate the working process of DME DI engine in engineering area. The author wrote the simulation program of Fortran based on theory of GASJET as well, and calculated the development of LPG spray in the constant volume chamber. The result of calculation and experiment are agreed well, and the GASJET model can provide valuable theoretic foundation with the design and development of LPG DI engine. The paper also presents a new reduced chemical kinetic model of DME for Homogeneous Charge Compression Ignition (HCCI) engine. This model consists of 28 species and 38 reactions, and includes three sub-models, i.e., low temperature and negative temperature coefficient region sub-model, pyrolysis and oxidation sub model of high temperature, and sub-model of formic acid generating process. By analysis of calculated result, the reduced model can predict the change of main species during the combustion of DME reasonably, and it also can get the correct results of heat release characteristic time of low and high temperature stage. Comparison with detailed model, the reduced model can save a lot of calculation time and its calculated results agree well with the results of detailed model. This study shows that chemical kinetics simulation for HCCI combustion of DME using the present reduced model coupled with CFD is attainable.