柴油机捕集器结构参数对不同粒径微粒过滤特性的影响

Effects of Diesel Particulate Filter Structural Parameters on Filtration Performance of Different Size Particles

基于孤立捕集体对柴油机排气微粒的微观捕集机理、单个多孔介质过滤层对微粒的宏观捕集模型和壁流式捕集器的微粒过滤机理,建立整体壁流式柴油机微粒捕集器的过滤模型,研究捕集器结构参数对不同粒径排气微粒过滤特性的影响。结果表明扩散捕集机理在整个微粒捕集中占支配地位,惯性碰撞和拦截机理的作用也不容忽视。粒径在10nm左右的微粒过滤效率最高,随着粒径的增加过滤效率下降,在0.5μm左右达到一个波谷值,粒径继续增大到1μm左右的微粒过滤效率又有所上升,表明扩散、惯性碰撞和拦截机理的复合捕集作用。随着过滤体宏观结构参数孔密度、壁厚、直径和长度的增加,各不同粒径微粒的过滤效率上升幅度各异。随着过滤体微观结构参数壁面孔隙率和微孔孔径的降低,不同粒径微粒的过滤效率都在迅速提高。所得结论对通过捕集器结构参数的优化匹配,以改进捕集器过滤性能具有重要理论意义和实用价值。

In this study, microcosmic capturing mechanism of single unit on diesel engine particles is firstly studied, then, macroscopical filtration model of single porous medium bed and trap model of monolithic wall-flow diesel particulate filter （DPF） on particulate matter （PM） are developed and formulated. Effects of main DPF structural parameters on filtration performance of different size particles from diesel engines are studied. The results show that the trap efficiency of 10 nm diameter particles is highest, and the efficiency descends while the particle diameter increases. The trap efficiency will be lowest near 500 nm diameter particles, and the trap efficiency ascends with particles diameter increasing to 1 pan continuously. This indicates the complex effects of diffusion, inertia and interception mechanisms on particle trap. With increasing cell density, wall thickness, diameter and length of filters, the filtration efficiencies of different size particles ascend with different extents. The trap efficiencies rapidly increase with decreasing porosity and mean pore size of filter substrates. These results are valuable for matching DPF structural parameters and improving filtration performance of DPF.