Filtration Behavior of Diesel Particulate Filters (1) 2007-01-0921

This paper is Part-1 of two papers discussing the filtration behavior of diesel particulate filters. Results of the fundamental study are presented in Part-1, and test results for real size DPFs are reported in the supplement, Part-2. In this paper, a fundamental experimental study was performed on the effect of pore size and pore size distribution on the PM filtration efficiency of the ceramic, wall-flow Diesel Particulate Filter (DPF). Small round plates of various average mean pore sizes (4.6, 9.4, 11.7, 17.7 micro-meters) with a narrow pore size distribution were manufactured for the tests. During the DPF filtration efficiency tests, ZnCl₂ particles in the range of 10 nm to 500 nm were used instead of PM from actual diesel engine exhaust. ZnCl₂ particles were made using an infrared furnace and separated into monodisperse particles by DMA (Differential Mobility Analyzer). Various ZnCl₂ particle sizes were introduced upstream of the test plates and particle numbers were counted at the upstream and the downstream positions to determine filtration efficiency. In addition, theoretical calculations were made for the collection mechanisms of i) diffusion, ii) interception and iii) inertia. The theoretical calculations were compared with the experimental test results. On-engine testing of a DPF, with optimum pore size distribution, demonstrated overall filtration efficiency of >90% during preconditioning operation of the NEDC test cycle. The potential of the deep-bed filtration model for predicting filtration efficiency of wall-flow type ceramic DPFs was confirmed. Additional vehicle tests were performed on DPFs with various pore structures. The results are shown and discussed in the Part-2.