Characterization of Oxidation Behaviors and Chemical-Kinetics Parameters of Diesel Particulates Relevant to DPF Regeneration 2010-01-2166

At the current stage of engine technology, diesel engines typically require diesel particulate filter (DPF) systems to meet recent particulate emissions standards. To assure the performance and reliability of DPF systems, profound understanding of filtration and regeneration mechanisms is required. Among extensive efforts for developing advanced DPF systems, the development of effective thermal management strategies, which control the thermal runaway taking place in oxidation of an excess amount of soot deposit in DPF, is quite challenging. This difficulty stems mainly from lack of sufficient knowledge and understanding about DPF regeneration mechanisms, which need detailed information about oxidation of diesel particulate matter (PM). Therefore, this work carried out a series of oxidation experiments of diesel particulates collected from a DPF on a diesel engine, and evaluated the oxidation rates of the samples using a thermo-gravimetric analyzer (TGA). First, chemical-kinetics parameters, such as activation energy and reaction order, were evaluated for diesel particulates, and then compared with those of commercial-grade model soot. From the experimental results with the model soot, an oxidation rate equation was defined by evaluating a reaction order of 0.78 ± 0.03 and an activation energy of 138 ± 16 kJ/mol. However, the oxidation of dry diesel soot represented two distinct oxidation zones through the entire oxidation period, where two sets of reaction order and activation energy were evaluated to be 0/154.1 kJ/mol and 0.8/152.6 kJ/mol, respectively. In the continuing experimental work, a differential scanning calorimeter (DSC) was used to measure the instantaneous heat flows of samples during oxidation. The DSC measured the amount of heat flow released during the oxidation and also differences in heat release between soluble organic fraction (SOF)-containing soot and dry soot. In these DSC experiments, the heat flow from the oxidation of dry diesel soot samples was measured to be 17.2 kJ/g in average, which was much higher than that from the oxidation of SOFs (5.5 kJ/g).