Abstract
Keywords - SCR, control, urea, ammonia, NOx
Abstract - Selective catalytic reduction (SCR) systems consuming urea solution for the removal of nitrogen oxide (NOx ) from the exhaust gases of power plants are prevalent and have a proven record. The transfer of this technology to mobile applications, however, poses additional difficulties and increases the challenge to the hardware as well as the software of such systems.
Power plants run at steady-state for long periods. With relatively simple control algorithms, most of the NOx is removed. In contrast, the mainly dynamic operation of mobile applications, together with the need to limit size and weight of the aftertreatment systems, calls for new solutions.
This paper concentrates on the design of advanced model-based control strategies. Among the new elements introduced are a dynamic model for the formation of NOx and several model-based feedforward controllers. An electronic filter for the signal of an NOx gas sensor is presented as well. While this sensor resists the harsh environment of a tailpipe, it is cross-sensitive against ammonia.
With the NOx filter, the implementation of a feedback controller becomes possible in mobile applications.
Finally, a step-by-step procedure is presented which leads through the design process for SCR control strategies.