Modeling and Controlling Active Regeneration of a Diesel Particulate Filter

Heavy soot deposition in wall-flow type diesel particulate filters reduces engine output and fuel efficiency. This necessitates forced regeneration to oxidize soot via exothermic reactions in a diesel oxidation catalyst upstream of the Diesel Particulate Filter (DPF). Soot loading in the wall of the DPF during forced regeneration causes much greater pressure drops than cake deposition, which is undesirable because high pressure drops reduce engine performance. We show that the description of soot deposition using a DPF model is improved by using a shrinking sphere soot oxidation sub-model. We then use this revised model to analyze cake deposition during forced regeneration, and to study the effects of varying the forced regeneration temperature and duration on the local soot reaction rate and soot mass distribution in the radial and longitudinal directions of the DPF channels during forced regeneration. Our results show that if the forced regeneration temperature is too high, the cake in the center of the DPF is oxidized and disappears, and the soot is redeposited in the wall, leading to deep bed filtration that increases pressure loss and reduces engine output. Therefore, the forced regeneration temperature and duration must be chosen carefully to preserve the cake during forced regeneration. We additionally propose a method to prevent soot from accumulating at the wall by varying the temperature during forced regeneration. It is shown that this approach can reduce forced regeneration times while avoiding re-deposition of soot at the wall.