Development of Improved SCRonDPF Design for Future Tighter Regulations and Reduced System Packaging 2018-01-0344
With the push towards more stringent on-road US heavy duty diesel regulations (i.e. HD GHG Phase 2 and the proposed ARB 20 mg/bhp-hr NOx), emission system packaging has grown critical while improving fuel economy and NOx emissions. The ARB regulations are expected to be implemented post 2023 while regulation for EU off-road segment will begin from 2019. The regulation, called Stage V, will introduce particle number (PN) regulation requiring EU OEMs to introduce a diesel particulate filter (DPF) while customer demands will require the OEMs to maintain current emission system packaging. A viable market solution to meet these requirements, especially for EU Stage V being implemented first, is a DPF coated with a selective catalyst reduction (SCR) washcoat (i.e. SCRonDPF). With SCRonDPF, a NOx reduction benefit is achieved while maintaining system packaging but, there is an increase in pressure drop due to the higher washcoat loading (WCL) for the SCRonDPF compared to a catalyzed soot filter (CSF). This paper first focuses on a parameter study to develop an improved Cordierite SCRonDPF design to reduce pressure drop while maintaining other key performances. A high porosity material (65%), 12 mil wall thickness (WT), 300 cells per square inch (cpsi) cell density, with a square shaped cell structure (12/300SQ) was used as the baseline. The design parameters evaluated include the pore size distribution (PSD), mean pore size (MPS), cell shape, cell density (CPSI), WT, and washcoat technology. Engine tests conducted were soot loaded pressure drop up to 6 g/L soot loading, active regeneration conducted at 600 °C, passive regeneration conducted at 350 °C, and PN filtration and NOx conversion efficiency performed on the Non-Road Transient Cycle (NRTC). Results from the parameter study show 12 mil/300 cpsi asymmetric (ASY) cell structure with a lower MPS and sharper PSD material, in combination with an improved catalyst, is the optimal SCRonDPF filter design achieving a pressure drop approximately 55% compared to the baseline SCRonDPF filter. The optimized SCRonDPF system pressure drop achieved closer to the production CSF system but still approximately 10% higher.