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Due to its better fuel efficiency and low CO2 emissions, the number of diesel engine vehicles is increasing worldwide. Since they have high Particulate Matter (PM) emissions, tighter emission regulations will be enforced in Europe, the US, and Japan over the coming years. The Diesel Particulate Filter (DPF) has made it possible to meet the tighter regulations and Silicon Carbide and Cordierite DPF's have been applied to various vehicles from passenger cars to heavy-duty trucks. However, it has been reported that nano-size PM has a harmful effect on human health. Therefore, it is desirable that PM regulations should be tightened. This paper will describe the influence of the DPF material characteristics on PM filtration efficiency and emissions levels, in addition to pressure drop.

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).

The application of Diesel Particulate Filters (DPF's) is expanding in the European, Japanese and US markets to comply with the tighter PM regulations. SiC DPF's, featuring greater robustness, have been applied extensively to passenger cars and are expanding into larger sizes for Light Duty Trucks applications. The SiC-DPF has higher mechanical strength when compared to other materials, such as Cordierite. However, SiC's thermal expansion ratio is greater. Therefore, the SiC-DPF is designed with 35 X 35mm segments and cement bonded construction, both of which function to relieve thermal stress. The appearance of the SiC-DPF with the segment design is shown in Figure 1. In this paper, the thermal stress mechanism of the segmented joint during soot regeneration and the influence of the cement properties on the thermal shock resistance was investigated by using the soot regeneration model and thermal stress analysis in addition to the engine test.