Simulation Study On The Influence Of Boundary Conditions On Combustion And Emission Of Gasoline Compression Ignition Engine

After more than one hundred years of rapid development,traditional gasoline and diesel engines have been pursuing the purpose of high efficiency and low pollution under continuous structural transformation and technological innovation.However,as the world’s oil reserves are declining,the unimproved internal combustion engine has been unable to meet people’s needs,and more scholars are focusing on new fuels and new combustion technologies.The gasoline low-temperature compression ignition(HCCI)technology is a new type of combustion mode,which not only has higher combustion efficiency,but also lower NOx and soot emissions,at the same time,including RCCI,SPCCI,etc,has always been the key points of its research for the past few years.The main content of this paper is to study the effect of different control parameters on the combustion and emissions of HCCI through intake air heating and internal EGR heating methods,and analyze the effect of different control parameters on its sensitivity.In this study,the model was created based on a modified ZR180 engine,through3 D scanning,reverse modeling technology,Hypermesh,CONVERGE and other software,and the model was verified by combining the data from real machine tests.In order to study the influence of intake air heating on gasoline low-temperature compression ignition,this paper selects three boundary parameters: intake air temperature,excess air coefficient,and coolant temperature.The upper and lower boundaries of gasoline low-temperature compression ignition at 1200r/min are used to analyze combustion and emission laws.The main conclusions are: increasing the intake temperature can advance the starting point of combustion,increase the maximum burst pressure in the cylinder,and reduce HC and CO emissions,but NOx are increased,and the sensitivity of the cylinder pressure peak near the upper boundary to the change of intake temperature is higher than that of the lower boundary.The sensitivity of CO and HC is reduced.But the sensitivity of NOx is gradually reduced at the lower boundary with the variety of intake temperature,while it is improved at the upper boundary;Increasing the excess air coefficient can reduce the maximum burst pressure and the average temperature in the cylinder,and delay the starting point of combustion.After the excess air coefficient is 1.9,the sensitivity of the upper boundary of the cylinder pressure is greater than that of the lower boundary.In terms of NOx emission sensitivity,these two loads change irregularly with the increase of excess air coefficient,but the upper boundary is more sensitive;Increasing the coolant temperature can advance the start of combustion.The upper boundary cylinder pressure peak sensitivity shows a downward trend,and the lower boundary cylinder pressure peak sensitivity is insensitive to the change of the coolant,while the NOx emission sensitivity both changes trends.Almost the same,but the upper boundary is more sensitive;In the case of the coupling of intake air temperature,excess air coefficient,coolant temperature and speed,the inlet temperature and rotational speed have the most affected on combustion,while the coolant temperature is the least,and the excess air coefficient has the greatest influence on HC and NOx emissions.The biggest influence on CO emissions is the intake air temperature.In order to study the influence of internal EGR on low-temperature compression ignition of gasoline,this paper uses a set of variable valve mechanism developed by the research group and applies the negative valve overlap strategy to intercept internal EGR to realize low-temperature compression ignition of gasoline.The study found that: This set of mechanism can achieve low-temperature compression ignition of gasoline with a negative valve overlap angle between-12°CA and-51.5°CA;By analyzing the laws of cylinder pressure,cylinder temperature,and heat release rate,it is found that there is a value for the EGR rate.Exceeding this value will inhibit combustion,and below this value will promote combustion.The specific value needs to be explored by improving the experiment.