Optimal NH3 Storage in SCR Catalysts

Maruthi  Devarakonda, Pacific Northwest National Laboratory

NH3 storage is an important control variable for high NOx conversion across the catalyst and therefore it is critical to maintain optimal set-levels of NH3 in the catalyst, such that stored NH3 does not desorb during transients (from low to high temperature conditions, typically encountered during a drive cycle). One approach to maintain the levels is to design an optimal urea injection trajectory, which in addition to minimizing NOx and NH3 slip from the catalyst, would minimize the error between dynamic NH3 storage and set NH3 storage in the catalyst at a given operating condition. A literature review on optimal control strategies has been done and approaches that could yield optimal NH3 storage have been identified using either a linear or a nonlinear Hammerstein-Wiener model of the SCR. The control-oriented model is learned from the reduced order discrete SCR model developed at MTU and verified against reactor/engine data. Both MIMO and MISO configurations are considered for the learned model. Simulation results from model learning and from optimal NH3 storage strategies will be discussed.

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