Detailed Investigation of Soot Deposition and Oxidation Characteristics in a Diesel Particulate Filter Using Optical Visualization 2013-01-0528
Detailed soot deposition and oxidation characteristics in a diesel particulate filter (DPF) have been experimentally examined on a unique bench-scale DPF test system that has a visualization window. The filtration and regeneration processes were visualized to examine soot deposition and oxidation behaviors on the filter channel surfaces, along with measurements of pressure drop across the filter. The pressure drop caused by trapped soot was separated from the measured total pressure drop by subtracting the pressure drop caused by the clean filter itself. Then, the soot-derived pressure-drop data, normalized (non-dimensionalized) by the volumetric flow rate, exhaust gas viscosity, and DPF volume, were used to compare filtration and regeneration characteristics at different experimental conditions, independently of flow conditions. Consequently, the normalized form of the pressure drop was able to be used as an intrinsic parameter defining soot cake characteristics, which is not influenced by engine speed/load conditions. In the analysis of pressure-drop data, we were able to identify three distinct filtration stages (depth filtration, transition filtration, and soot cake formation); the subsequent regeneration process exhibited three distinct pressure-drop behaviors as well. In conjunction with the normalized pressure-drop data, the visualized soot images helped us illuminate the details of soot deposition and oxidation phenomena at each stage. Finally, it was found that most of the soot deposits in micro-pores were likely to be oxidized at an initial regeneration stage and the pressure drop decreased most significantly during the second regeneration stage, when a majority of effective pores open. Then remaining soot cake on the wall was completely oxidized in a monotonic decrease of pressure drop during the last regeneration stage, returning the filter to the initial clean condition.