The Development of Advanced 2-Way SCR/DPF Systems to Meet Future Heavy-Duty Diesel Emissions

Diesel engines have the potential to significantly increase vehicle fuel economy and decrease CO₂ emissions; however, efficient removal of NO_x and particulate matter from the engine exhaust is required to meet stringent emission standards. A conventional diesel aftertreatment system consists of a Diesel Oxidation Catalyst (DOC), a urea-based Selective Catalyst Reduction (SCR) catalyst and a diesel particulate filter (DPF), and is widely used to meet the most recent NO_x (nitrogen oxides comprising NO and NO₂) and particulate matter (PM) emission standards for medium- and heavy-duty sport utility and truck vehicles. The increasingly stringent emission targets have recently pushed this system layout towards an increase in size of the components and consequently higher system cost. An emerging technology developed recently involves placing the SCR catalyst onto the conventional wall-flow filter. This technology enables reduced aftertreatment system volume and mass when compared to the conventional SCR system architecture. This technology also offers the potential of cost savings and packaging flexibility. In this work, the potential of the Cu/Zeolite-based SCR/DPF technology for meeting future emission standards was evaluated on a heavy-duty diesel engine operating on an engine dynamometer. In addition, a laboratory fixed-bed flow reactor system was used to determine the NH₃ storage characteristics and the SCR performance as a function of soot loading and catalyst aging.