A Real-Time Control Framework for Integrated Diesel Engine and Selective Catalytic Reduction System

Diesel engines have been widely adopted in medium- to heavy-duty ground vehicles, due to high engine efficiency, high power output, and superior reliability. However, as Diesel engine emission regulation has been significantly tightened in the past decade, emission control has become a major barrier for Diesel engine efficiency improvement. Integrated Diesel engine and aftertreatment system controls are very important for modern Diesel engines to further improve fuel efficiency while facing increasingly stringent NO_x and particulate matter (PM) emission regulations. In this paper, a real-time implementable, integrated engine-aftertreatment control framework was proposed to coordinate a modern Diesel engine with the coupled urea-based selective catalytic reduction (SCR) system for achieving close-to-optimal engine efficiency while meeting tight tailpipe NO_x and NH₃ slip requirements. With engine-out NO_x emissions being considered as an additional active control input (other than urea solution injection rate) to the SCR system, both engine fuel efficiency and tailpipe emissions were incorporated in the new multi-input SCR control problem formulation. Nonlinear backstepping-based control allocation algorithms were designed to intentionally increase engine-out NO_x emissions without sacrificing the tailpipe emission control performance. With the relaxed engine-out NO_x emission constraint, engine start of injection (SOI) timing control was optimized for achieving higher engine efficiency. Simulation results based on experimentally calibrated Diesel engine and aftertreatment system models demonstrated significant fuel saving by 10.86% over the transient US06 cycle with the proposed integrated control, compared to an isolated Diesel engine control. In addition, the computationally-efficient integrated control algorithms can be implemented on the existing engine control units for realizing the fuel saving and emission control benefits in the near future.