Coating distribution in a commercial SCR-filter
Mark Stewart, PNNL
Tightening exhaust emissions standards and rising fuel efficiency requirements are necessitating continued development of exhaust aftertreatment technologies. In order to reduce costs and save scarce space on vehicles, there is considerable interest in combining multiple aftertreatment functions into fewer units in the exhaust system. One such technology is the combined SCR catalyst and particulate filter. This concept involves significant challenges, not the least of which is loading a sufficient volume of the relatively bulky SCR catalyst into the filter without causing unacceptably high back-pressures, especially as the filer becomes loaded with soot and ash.
A commercial SCR-filter, deployed in the US in 2015, has been sectioned and examined. Preliminary observations indicate at least three different coating regimes along the honeycomb monolith, which would likely result in different exhaust flow dynamics and catalytic activities per volume. Accurate modeling of the performance of these multi-functional devices will be necessary for optimal system design, requiring realistic representation of transport phenomena and reaction rates within the unit.