过滤壁结构对颗粒捕集器深床过滤影响的模拟

Simulation on influence of microstructure of the wall on deep bed filtration of particulate filter

针对汽油机颗粒捕集器的动态捕集过程及性能,采用孔径分布概率密度函数以及孔隙率分布函数表征多孔介质的非均匀微观结构,并引入对数正态分布描述入射颗粒粒径分布,研究多粒径颗粒入射状态下过滤壁微观结构对GPF深床过滤过程的影响。结果表明:颗粒物大部分沉积于多孔壁上部1/3左右区域,孔径增大会导致沉积位置向下扩大以及孔隙率、渗透率分布的均匀性提高,而孔隙率变化则对颗粒沉积位置影响较小;相对于孔隙率变化,多孔介质的捕集效率及压降性能对于孔径变化的敏感性更高;大孔隙率小孔径结构的多孔介质具有较高的捕集效率与最好的压降性能。

Gasoline direct injection(GDI) engine cars are widely welcomed by the market due to their outstanding fuel economy and engine power density. However,compared to traditional port injection engines and diesel engines equipped with diesel particulate filter(DPF),GDI engines have higher particulate emissions. Therefore, countries around the world have enacted laws to limit particulate emissions. Gasoline particulate filter(GPF)is an effective solution to the problem of particulate matter emission. Aiming at the dynamic filtration process,filtration efficiency and pressure drop performance of the gasoline particulate filter,the probability density function(PDF)of the pore size distribution and the piecewise function of the porosity distribution are used to characterize the heterogeneity of the microstructure of the porous medium. The log-normal distribution is introduced to describe the particle size distribution of incident particles,and the influence of the filter wall microstructure on the GPF deep bed filtration process under the condition of multi-particle size incident is studied. The results show that the porous medium is saturated from the upper 1/6 area,and most of the particles are deposited in the upper 1/3 area of the porous wall. The increase of the pore size will lead to the downward expansion of the deposition position,the decrease of the first saturated layer and the improvement of the uniformity of the porosity distribution,while the change of the porosity will have a small effect on the particle deposition position. The filtration performance and pressure drop performance of porous media show a trade-off relationship. Compared with porosity changes,the filtration efficiency and pressure drop performance of porous media are more sensitive to changes in pore size,and the porosity has little effect on the initial filtration efficiency. The porous media with large porosity and small pore size has higher filtration efficiency and the best pressure drop performance.