Non-Uniform Cylinder-to-Cylinder Combustion for Ammonia Generation in a New Passive SCR System

Abstract

Lean burn gasoline engine is a promising technology for reducing the fuel consumption by passenger cars. However, cost-effective NOx emissions control for lean burn gasoline engines remains a great challenge for the commercialization of lean burn gasoline engines in the U. S. market. To address this issue, passive selective catalytic reduction (SCR), which utilizes a close-coupled three-way catalyst (TWC) as an on-board device for ammonia (NH3) production during rich engine operation, has attracted much attention in the past several years. The main purpose of this study is to reduce the cost of ammonia generation for a passive SCR system by proposing a new passive SCR system architecture and an innovative non-uniform cylinder-to-cylinder combustion (NUCCC) strategy. The new passive SCR system that consists of a two-stage TWC and a TWC bypass, together with the optimization of NUCCC strategy, can potentially enable more efficient engine combustion and more cost-effective ammonia production. Optimization results based on the experimental data from a physical engine platform, demonstrate that the proposed new passive SCR system coupled with the NUCCC strategy, can reduce the ammonia specific fuel consumption (ASFC) by up to 29.8%. Such a novel engine combustion strategy and innovative aftertreatment system can be very instrumental in significantly reducing the fuel penalty associated with NOx emission control for lean-burn engines in the future.