Optimization of Mode Switching Timing Control for a Lean-Burn Gasoline Engine With a Prototype Passive SCR System

Passive selective catalytic reduction (SCR) has emerged as a promising NO_x reduction technology for highly-efficient lean-burn gasoline engines to meet stringent NO_x emission regulation in a cost-effective manner. In this study, a prototype passive SCR which includes an upstream three-way catalyst (TWC) with added NO_x storage component, and a downstream urealess SCR catalyst, was investigated. Engine experiments were conducted to investigate and quantify the dynamic NO_x storage/release behaviors as well as dynamic NH₃ generation behavior on the new TWC with added NO_x storage component. Then, the lean/rich mode-switching timing control was optimized to minimize the fuel penalty associated with passive SCR operation. Simulation results show that, compared to the baseline mode-switching timing control, the optimized control can reduce the passive SCR-related fuel penalty by 6.7%. Such an optimized mode-switching timing control strategy is rather instrumental in realizing significant fuel efficiency benefits for lean-burn gasoline engines coupled with cost-effective passive SCR systems.