Investigation of NOx- and PM-reduction by a Combination of SCR-catalyst and Diesel Particulate Filter for Heavy-duty Diesel Engine

The upcoming Euro VI emission legislation for Heavy Duty Diesel engines can be complied with by using a combination of a wall flow DPF and a UREA SCR-system. This paper describes investigations of NO_x and PM reduction by a combination of SCR-catalyst and an (uncoated) Diesel particulate filter (DPF), performed on a fully transient heavy-duty test bench. Soot loading and passive regeneration of the DPF for different configurations of both components and active regeneration by fuel injection into the exhaust gas line were investigated. The impact of DPF on SCR-catalyst as well as SCR-catalyst impact on DPF was analyzed in terms of NO_x-conversion and regeneration efficiency of the filter under steady-state and transient operating conditions.

The NO_x-conversions for the configuration SCR-catalyst in front of DPF were higher for all operating conditions than for the combination DPF in front of SCR-catalyst. This was due to higher temperatures and higher NO₂-to-NO_x-ratios in front of the SCR-catalyst. On the other hand, passive regeneration of the filter in this configuration was poor under certain operating conditions due to low concentrations of NO₂ in front of the DPF. For the combination DPF in front of SCR-catalyst, passive regeneration of the filter was sufficient in a wide range of the operating conditions.