Integrated diesel engine and selective catalytic reduction system active NOx control for fuel economy improvement

Diesel engine technologies have gone through significant progresses in the past decade. Though the tailpipe NO_x and particulate matter emissions have been reduced to a large extent by the applications of after-treatment systems such as selective catalytic reduction (SCR) systems and Diesel particulate filters, engine fuel economy usually needs to be compromised considerably to achieve appropriate engine-out emissions. Most of the current Diesel engine control studies focus only on the Diesel engines themselves, while most of the current aftertreatment controls are limited in the scope of aftertreatment systems alone. The opportunities of further improving the overall powertrain system performance by considering the engine and aftertreatment system in an integrative way have been rarely exploited. In this paper, a new framework for integrated control of both engine and aftertreatment system is devised. A backstepping-based active NO_x control method is proposed by treating the engine-out NO_x concentration as a control input for the ammonia coverage ratio control of a two-cell SCR system. Simulation results based on the UDDS driving cycle show that up to 5.86% of engine fuel consumption can be reduced without a significant penalty on the tailpipe emissions.