Close Coupled Catalyzed Soot Filters for Passenger Vehicles

To comply with worldwide global emission standards, Catalyzed Soot Filters (CSF) have been applied in a number of different configurations on passenger vehicles. To meet the regulated Hydrocarbon (HC) and Carbon Monoxide (CO) emissions, Diesel Oxidation Catalysts (DOC) were used in conjunction with a CSF to treat the particulate emissions. To reduce the amount of emission control hardware on a vehicle, OEMs have been looking at simplifying DOC+CSF systems or moving to CSF only catalysts. The progress made in this area over the past few years will be explained.

More compact or reduced volume emission control hardware requires that the DOC functionality be integrated on the CSF in order to meet gas phase CO and HC emissions. First generation soot filters were not designed to accept high levels of catalytic coatings and still meet engine back pressure requirements. New filter structures with higher porosity and more favorable pore size distributions can accept the higher oxidation coating levels that enable the filter to do the DOC functions. By combining engine technology with advanced CSF designs, more compact and cost efficient systems can be realized.