Dynamic Control of Engine NOx Emissions: Characterization and Improvement of the Transient Response of an Exhaust Gas Recirculation System

An effective method for reducing NOx emissions from automotive engines is to use exhaust gas recirculation (EGR) to dilute the inducted air-fuel charge. Previous work has shown that degraded propagation delay and rise time characteristics of an EGR system can result in increases in NOx emissions for engine operation over dynamic rpm/torque versus time trajectories as exemplified by the Federal Test Procedure driving cycle. In an effort to improve the dynamic response of a production-like electronically controlled EGR system, the EGR system was characterized and a transient compensation scheme to improve its dynamic reresponse was implemented in a computer-based EGR controller. For an aggressive EGR schedule, the compensated EGR system had equivalent NOx control capability without the transient torque disturbances exhibited by the uncompensated system.