For diesel exhaust aftertreatment applications with space limitations, as well as to move the selective catalytic reduction system (SCR) to a warmer location closer to the engine, DOC on CSF technology can be used. This technology combines the diesel oxidation catalyst (DOC) and catalyzed soot filter (CSF) functionalities in one component, thereby enabling volume reduction. DOC on CSF maintains the abatement of hydrocarbon (HC), carbon monoxide (CO), and particulate matter (PM), and the oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) for passive soot oxidation and fast SCR reaction of NOx on a downstream SCR catalyst. In this study, the performance of DOC on CSF was compared to a DOC + bare diesel particulate filter (DPF) and a DOC + CSF system, to understand the performance benefits and challenges.
All the components were optimized individually for their respective functions. The DOC on CSF was optimized for NO oxidation and passive soot oxidation performance. Experimental data and simulations were used to understand the underlying mechanisms in the DOC on CSF technology. Steady state HC oxidation under active regeneration conditions showed a benefit for DOC on CSF compared to the DOC + DPF system. The soot oxidation characteristics of the DOC on CSF were evaluated in comparison to a DPF or CSF downstream of a DOC under passive and active soot oxidation conditions. In addition, the contribution of NO2 generated within the filter on the soot oxidation was assessed. The passive soot oxidation characteristics of a DOC on CSF were found to be similar, or better, compared to DOC + DPF and DOC + CSF under certain conditions. The active regeneration efficiency was lower for the DOC on CSF due to the gradual increase in temperature along the length of the part during fuel injection. This work demonstrates the differences between the DOC on CSF and DOC + bare/coated DPF systems, thus enabling a better understanding of the performance of DOC on CSF to current applications.