The Development of Advanced Urea-SCR Systems for Tier 2 Bin 5 and Beyond Diesel Vehicles 2010-01-1183

An advanced diesel aftertreatment system utilizing Selective Catalytic Reduction (SCR) with urea for lean nitrogen oxides (NO_x) control was tested on a 2.7L V6 Land Rover vehicle to demonstrate the capability of achieving Tier 2 Bin 5 and lower emission standards for light-duty trucks. SCR washcoat was applied to a diesel particulate filter (DPF) to perform NO_x and particulate reduction simultaneously. Advanced SCR systems employed both traditional SCR catalysts and SCR-coated filters (SCRF) to improve the NO_x reduction efficiency. The engine-out NO_x level was adjusted by modifying the EGR (Exhaust Gas Recirculation) calibration. Cold start NO_x performance was improved by SCR warm-up strategy and urea over injection. This study showed the advanced SCR system could tolerate higher NH₃ storage in the SCR catalyst, resulting in overall higher NO_x conversion on the FTP-75 test cycle. With a modified strategy, the aftertreatment system (oven aged to represent 120k mi) achieved 0.046 g/mi for NO_x tailpipe emission and 0.023 g/mi for NMHC tailpipe emission.