Observer-Based Estimation of Diesel Engine Aftertreatment System NO and NO₂ Concentrations

This paper presents an observer design for Diesel engine aftertreatment system NO and NO₂ concentrations estimations. NO and NO₂ have different reaction characteristics within SCR systems. Current production NO_x sensors cannot differentiate NO and NO₂. Such an observer thus can be used by selective catalytic reduction (SCR) system control and diagnosis purposes. Diesel oxidation catalyst (DOC) and Diesel particulate filter (DPF) were considered as the catalysts which can affect NO/NO₂ fraction of the exhaust gas upstream of the SCR. The observer was designed based on an experimentally-validated control-oriented dynamic model which can accurately represent the NO and NO₂ dynamics from engine-out, through DOC, and to DPF. Stability of the observer was theoretically proved through a Lyapunov analysis assisted by insight into the system characteristics. The effectiveness of the observer was shown by comparing the estimated NO and NO₂ concentrations with the measured ones by a Horiba emissions measurement system.