Ammonia cross-sensitivity detection in SCR catalyst using state estimation

Reducing emissions in a cost effective manner is important for the marine industry and with even stricter legislation on the way, promoting new green fuels, control of aftertreatment catalyst systems will play a vital role. In this paper, the focus is on selective catalytic reduction systems and how state estimation can be applied to known challenges. The difficulty of measuring the ammonia storage inside an SCR catalyst is addressed with a Kalman filter state estimator capable of fast simulation due to a simplified, yet detailed enough, prediction model. The testing and development of multiple Kalman filters on standard diesel engine configurations, aim at future use cases, in particular ammonia fueled marine engines. The accuracy of the proportional-integral extension of the Kalman filter and the proposed NOx sensor cross-sensitivity estimator are of significance, especially as more ammonia is introduced to the SCR catalyst as a result of ammonia being used as fuel. Overall, the suggested variations of the SCR state estimator show high potential to estimate the NOx and ammonia outputs from the catalyst with satisfying precision and real-time-ready computational load.