Study On Particulate Emission Characteristics Of GDI Engine And Optimization Of Gasoline Particulate Filter

With the wide application of gas direct injection technology in the supercharged small gasoline engine,the problem of high particulate matter emission is getting prominent.GDI engines that only adopt interior purification technology can hardly meet the increasing stringent requirements claimed in the legislative test cycle,which to some extent promotes the development of research on this field.Therefore,the application of gasoline particulate filter(GPF)is going to be one of the important means for a stricter emission regulation.First of all,this paper explained the development process of domestic and international emission regulations for the emission limits of particulate matter of GDI engine.The formation mechanism were also studied,and the structure,material and basic characteristics of GPF were introduced.In this thesis,the PM emission character of GDI engine was experimentally studied to optimize the overall structure of GPF and the microscopic pore structure of filter by numerical simulation.The main research contents are as follows:Firstly,the development of PM regulation,the PM generation principle and the technical route of emission control strategy were introduced.In addition,the structure,materials and basic characteristic of GPF were also explained.Secondly,the GDI gasoline engine test bench was built and the DMS-500 rapid response analyzer was utilized to study the particle number concentration and size distribution under different engine loads and speeds which provided data for subsequent GPF numerical simulation.In the logarithmic coordinates,the GDI engine emission contains a large number of nanoscale particles,corresponding to the nucleation mode region and the accumulation mode region according to the particle size.In the load characteristics and speed characteristics the GDI engine emission is different distribution respectively.Then,the pressure field,the temperature field,the velocity vector map and the velocity distribution cloud map of the selected engine in real working process were simulated based on computational fluid dynamics and flow noise study.Influences from working condition,filter length and inlet angel to GPF inter fluent field were analyzed.The steady and transient noise sources were studied after the detailed simulation of the fluent field was carried out.The impacts that engine working conditions and the inlet angel on GPF fluent noise were researched,after which the overall GPF structure was optimized.With a filter length of 91 mm and an inlet angel of 70 degree,the fluent field of GPF obtained uniform velocity distribution,reasonable pressure field and temperature field,together with low back pressure and flow noise.Finally,a calculation unit of the GPF filter part was intercepted to model the pore structure and simulate the velocity distribution,particle trajectory,pressure field,concentration distribution and capture characteristics among different time in the particle capturing process.By analyzing the influence of wall thickness and channel width on capturing process of the GPF filter and taking both the filter back pressure and the capture efficiency into consideration,a conclusion can be drawn that a pore structure with 0.2 mm wall thickness and 0.4 mm channel width had lower back pressure,better flow uniformity and higher capture efficiency.