Urea-SCR is an important part of the diesel engine aftertreatment to meet increasingly stringent NOx emission regulations. It works by reducing the engine-out NOx using NH3. Since it is difficult and dangerous to store NH3, diesel exhaust fluid (DEF), which is a mixture of urea and distilled water, is injected into the exhaust as a source of NH3. Too little urea will lead to insufficient deNOx and too much will lead to NH3 slip, which is a pollutant itself. Therefore, it is important to develop an effective urea-dosing control to inject optimum amount of urea at all times.

This paper presents two non-model-based reference-shaping and a model-based predictive urea-dosing controller for the Urea-SCR system. An ideal urea-dosing controller would minimize both tailpipe NOx and NH3 slip. However, this is not possible because of the trade-off between deNOx and NH3 slip. We use this trade-off to clearly define a control objective in terms of NH3 slip. We then develop three controllers to meet this control objective such that they are all computationally inexpensive. The three controllers are then tested for three very different drive cycles. Simulation results show that the performance of the non-model based reference-shaping controllers is subjected to manual tuning of their variables for each drive cycle. In contrast, the predictive controller, which is the highlight of this paper, can adapt to various drive cycles without compromising on the computational cost.


Computationally Efficient Urea-Dosing Controllers for Urea-Scr

Division / Sponsors: 
Dynamic Systems & Control (DSCD)

Paper Proceedings: https://asmedigitalcollection.asme.org/DSCC/DSCC2020/volume/84270

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