Monitoring, Feedback and Control of Urea SCR Dosing Systems for NOx Reduction: Utilizing an Embedded Model and Ammonia Sensing

This paper presents a monitoring, feedback and control system for SCR urea dosing utilizing an embedded model and NH₃ sensing after the SCR for loop closing control. A one-dimensional SCR model was developed and embedded in a Simulink/Matlab environment. This embedded model is utilized for on-line, real time control of 32.5% aqueous urea dosing in the exhaust stream. Engine testing and simulation are used with the embedded SCR model and NH₃ sensor closed loop feedback to demonstrate the advantages of this control approach for meeting both NO_x emission requirements and NH₃ slip targets. The paper explores these advantages under heavy duty FTP cycle conditions. The potential benefits include SCR size optimization and fuel consumption rate reduction under certain operating conditions.