Study On Partial Premixed Combustion Mode Of High Pressure Direct Injection Natural Gas Engine

High pressure direct injection natural gas engine has become the research focus of the corresponding industry because of its high thermal efficiency and low emissions.More and more attention has been paid to the research on the new combustion technology of natural gas engine to further improve its thermal efficiency and reduce its emissions.High pressure direct injection natural gas engines adopt natural gas as the main fuel,diesel as the pilot fuel,the combustion process of which involves the injection and evaporation of diesel,as well as the injection and combustion of natural gas,the physical and chemical reactions in the cylinder are very complex.Subsequently,investigating the effects of injection parameters on combustion and emissions of the engine can provide certain theoretical guidance for the optimization of the engineThe aim of this thesis is to explore the effects of injection parameters on the combustion and emissions of high pressure direct injection natural gas engines.The 3D numerical simulation model was developed,with which the effects of injection parameters on the combustion and emissions of the engines were investigated.The main research work and results are as follows:The test bench for high pressure direct injection natural gas engine was built and experimental investigations were conducted to obtain the dynamic,economic and emission characteristics of the engine.The experiment results indicated that:for high pressure direct injection natural gas engine,the thermal efficiency and NOx emissions both show a trend of increasing first and then decreasing with the increasing of the loads,while the trend of CO emissions is opposite and the THC emissions and CH4 emissions show a trend of decreasing at the same time.The combustion speed of diffusion combustion model is affected by the injection time of natural gas and the diffusion speed of natural gas.In addition,the rapid combustion period of engines is longer under large loads,thus it’s possible to improve the thermal efficiency by using reasonable combustion models.The 3D simulation model of high pressure direct injection natural gas engines was constructed,and the accuracy of the 3D simulation model was verified by comparing the simulation results of the 3D simulation model with the test results of the test bench.Numerical investigations to explore the effects of injection parameters on the combustion and emissions characteristics were carried out based on the 3D numerical simulation model.The simulation results indicated that:in the case that the proportion of pre-injection natural gas is less than 30%,increasing the proportion of pre-injection natural gas,reducing pre-injection advance angle and choosing the swirl ratio of 1.5 or 1.6 is conducive to promoting the combustion process in the cylinder and improving the combustion thermal efficiency.Lower CO emissions can be obtained by reducing the proportion of pre-injection natural gas and choosing moderate pre-injection advance angle under medium loads;and by increasing the proportion of pre-injection natural gas,reducing pre-injection advance angle under large loads.Lower NO emissions can be obtained by the same measurements as those of CO under medium loads;and by reducing the proportion of pre-injection natural gas,choosing moderate pre-injection advance angle under large loads.Additionally,lower SOOT emissions can be obtained by increasing the proportion of pre-injection natural gas under medium loads;and by increasing pre-injection ratio,choosing moderate pre-injection advance angle under large loads.