Simulation Study On Dynamic Filtration Process Of Particulate Filters For Gasoline Direct Injection Engines

Gasoline direct injection(GDI)engines have been widely used in light-duty vehicles due to advantages of better power output,fuel economy and dynamic driving responsiveness.However,GDI engines emit more particles than conventional port fuel injection gasoline engines and diesel engines equipped with particulate filters.Particles emitted by GDI engines are relatively small.These particles are abundant in the raw exhaust gas,which pose a great threat to air quality and human health.At present,not only particulate matter,but also particulate number for the GDI engine is regulated.The application of gasoline particulate filters(GPFs)is considered to be the most effective technical solution for the particle emission problem of GDI engines.The deposition distribution of particles in the GPF has a direct impact on filtration efficiency and pressure drop.The particles in the exhaust gas of GDI engines are very small and can penetrate into the porous wall.Therefore,the structure of porous media needs to be considered in the research.In order to represent the structure of porous media,a non-uniform porous wall model based on the probability density function of pore size distribution and porosity distribution is established.Considering the multiple diameters of inlet particles,the dynamic process of particle deposition and filtration performance of a GPF in deep-bed filtration are studied.The influence of porosity distribution and pore size distribution of the non-uniform wall and the influence of particle size distribution of inlet particles on the deep-bed filtration are further studied.The study on the evolution process of characteristic parameters of the porous wall in deep-bed filtration shows that the particle deposition mass,the collector diameter of each slab,the local porosity and permeability distribution over time are consistent with each other.The bottom of the porous wall contributes little to filtration,and most of the particles are deposited in the transition region at the top of the porous wall,which leads to smaller local porosity and permeability.With the increase of time,the tendency that filtration efficiency is higher for both small and large particles but lower for middle size particles becomes more obvious and filtration efficiency for particles larger than 70 nm is obviously improved,and the most penetrating particle size becomes smaller.In the study of the influence of porosity distribution of the porous wall on deepbed filtration,it is found that porosity distribution has an important influence on the position of the maximum deposition mass.The higher the slope of the transition region,the higher the position where the maximum deposition mass occurs,and the higher the deposition mass at the bottom of the porous wall.Smaller porosity difference will lead to a higher position where the maximum deposition mass occurs,but the value of the maximum deposition mass is lower and the mass of particles deposited at the bottom is comparatively higher.The mean porosity has little effect on the location of the maximum deposition mass.In the study of the influence of pore size distribution of the porous wall on deepbed filtration,it is found that pore size distribution has an important influence on the value of the maximum deposition mass.If the mean pore size is smaller,more deposition mass will be accumulated in the transition region,the maximum deposition mass will be larger,and the pressure drop growth rate will be higher.If the variance of pore size distribution is smaller,the maximum deposition mass will be larger,and the growth rates of filtration efficiency and pressure drop will be higher.In the study of the influence of particle size distribution on deep-bed filtration,it is found that within the same time period,the difference in filtration efficiency for particle clusters with different particle size distributions plays a major role in filtration under the same mass flow rate,while the difference in total mass of different particle size distributions plays a major role in filtration under the same number flow rate.When the mass flow rate is the same,particles mainly composed of 50 nm are deposited most in the porous wall,which make the porosity and permeability decrease more.When the particle number flow rate is the same,the porous wall has better filtration effect on small particles mainly composed of 50 nm and large particles mainly composed of 300 nm,but the latter has the highest deposition mass inside the porous wall,resulting in more pronounced changes in porosity and permeability.