Model-Based Control with Disturbance Compensation for a SCR Catalyst

Heavy-duty gas engines are used in industrial applications as well as to supplement the supply of green energy to meet peak demand for electricity and heat. Compliance with increasingly stringent emissions regulations necessitates the use of exhaust gas aftertreatment systems. In this context, engines equipped with selective catalytic reduction (SCR) catalysts, where nitrogen oxides are reduced using urea, are of particular interest. The paper proposes a model-based approach for controlling the outlet
$\mathbf{NO}_{\mathbf{X}}$
concentration in such catalysts. A distributed-parameter model for both the thermal and the kinetic subsystems explicitly accounts for the transport phenomena within the catalyst. Feedforward control and observer-based state feedback are based on a lumped-parameter approximation of the model equations. Both the controller and the observer use a linear quadratic (LQ) approach to compute feedback and output injection gains, respectively. In order to achieve stationary accurate tracking despite model uncertainties, the observer is extended to estimate constant disturbances. Experimental validation on a real engine is performed to compare the proposed model-based controller (MBC) with a standard proportional-integral-derivative (PID) controller.