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

Abstract

<div class="section abstract"><div class="htmlview paragraph">An advanced diesel aftertreatment system utilizing Selective Catalytic Reduction (SCR) with urea for lean nitrogen oxides (NO<sub>x</sub>) 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<sub>x</sub> and particulate reduction simultaneously. Advanced SCR systems employed both traditional SCR catalysts and SCR-coated filters (SCRF) to improve the NO<sub>x</sub> reduction efficiency. The engine-out NO<sub>x</sub> level was adjusted by modifying the EGR (Exhaust Gas Recirculation) calibration. Cold start NO<sub>x</sub> 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<sub>x</sub> 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<sub>x</sub> tailpipe emission and 0.023 g/mi for NMHC tailpipe emission.</div></div>