Design and Optimization of a Parallel Micro-Hybrid Vehicle with Lean-Burn Gasoline Engine and Passive SCR System

Lean-burn gasoline engines have demonstrated significant fuel saving benefits due to the reduced pumping loss under part-load operation, while NOx emission control in lean environment has become one of the major barriers. To reduce NOx emissions from lean-burn gasoline engine, passive selective catalytic reduction (p-SCR) systems have been introduced and the efficacy of p-SCR systems has been validated in various studies. One of the major challenges in a lean-burn gasoline engine with p-SCR system is the periodic mode switching from highly efficient lean operation to inefficient rich operation for ammonia generation. This study focuses on design and optimization of a micro hybrid electric powertrain which integrates the lean-burn gasoline engine with p-SCR systems (with and without NOx storage component on a three-way catalyst) into hybrid electric powertrain to enable more efficient engine operation. A novel active torque control-based ammonia generation strategy is proposed to reduce the fuel penalty associated with ammonia generation. Simulation results demonstrated that, by implementing the novel control strategy on the micro-hybrid powertrain system, the proposed hybrid electric powertrain can reduce the fuel penalty associated with p-SCR operation by up to 71%, in comparison to the conventional powertrain with the same lean-burn engine and aftertreatment system.