Model Based Control of SCR Dosing and OBD Strategies with Feedback from NH ₃ Sensors

This paper presents a model-based control system for SCR urea dosing employing an embedded real-time SCR chemistry model and a NH₃ sensor. The control algorithm consists of a number of control features designed to enhance ammonia storage control and closed-loop compensation using the mid-brick NH₃ sensor. An adaptive control algorithm is developed to demonstrate robustness of the feedback control system to compensate for catalyst aging, urea injection malfunction, or dosing fluid concentration variation. Simulation and engine dynamometer testing following ESC and FTP emission cycles are used to demonstrate the advantages of this control approach for meeting both NO_x emission requirements and NH₃ slip targets. Furthermore this paper demonstrates potential of a NH₃ sensor for on-board diagnostics. Additionally the feasibility of implementing model based algorithms in a 32-bit floating-point environment with an automotive controller is examined.