Visualization of Combustion Phenomena in Regeneration of Diesel Particulate Filter

Combustion phenomena in the regeneration of a diesel particulate filter (DPF) were clarified through a visualization experiment, using a half-cylindrical wall-flow DPF covered by a quartz glass plate. At a constant oxygen concentration (8.5% and 10% in the current study) of a working gas used for regeneration, in the cases of large particulate masses and high working gas temperatures, the particulate matter trapped on the filter surface is burned in a narrow reaction zone which can be observed as a high brightness zone moving slowly toward the downstream side. Just after the reaction zone passes, a sharp temperature peak is detected and there remains no particulate matter on the filter surface. Furthermore, the particulate matter is ignited first around the middle of the DPF, and then, the reaction zone propagates toward both the upstream and the downstream sides. On the other hand, in cases of small particulate masses and/or low working gas temperatures (but higher than 600°C), no such bright reaction zone is seen; however, it was observed that with time the particulate matter disappeared uniformly on the entire filter surface. These regeneration patterns can be summarized as separate and distinct reaction patterns in a reaction diagram consisting of the particulate mass and the inlet temperature of the working gas.