Catalyzed Soot Filters in Close Coupled Position for Passenger Vehicles

Recently, catalyzed soot filters (CSF) for passenger vehicles have been introduced into the marketplace to comply with the European environmental requirements and future emission standards. The initial system consisted of one or two diesel oxidation catalysts (DOC) to meet the regulated HC and CO standards along with an under floor CSF to treat the particulate emissions. In order to meet the cold start requirements and to reduce system costs with a CSF only unit, converters are placed closer to the engine to minimize heat losses and more of the DOC functionality is integrated into the filter substrate.

This work describes the development of such DOC-integrated CSF systems. One major challenge in the design of such systems is to ensure that there is sufficient catalyst functionality within the wall-flow substrate while maintaining an acceptable exhaust gas backpressure across the filter. It will also be demonstrated that specific catalyst and precious metal design architecture in conjunction with appropriate filter substrate selection leads to advanced CSF systems that can withstand the durability requirements of a soot filter environment after multiple soot regenerations. Aspects of soot accumulation and regeneration and its impact on system performance will be discussed as well.