Oxygen Concentration Dynamic Model Through a Diesel Engine Aftertreatment System

This paper presents a control-oriented model describing the dynamics of oxygen concentration through a Diesel engine aftertreatment system that includes a Diesel oxidation catalyst (DOC) and a Diesel particulate filter (DPF). Exhaust gas oxygen concentration is important for catalysts such as NO_x conversion efficiencies of selective catalytic reduction (SCR) systems and lean NO_x traps (LNT). In the presence of low-pressure loop exhaust gas recirculation (EGR), the exhaust gas oxygen concentration after-DPF also influences combustion. Due to the chemical reactions occurring inside DOC and DPF, the exhaust gas oxygen concentration considerably varies through the aftertreatment systems. Directly measuring the exhaust gas oxygen concentrations at different locations through the exhaust gas aftertreatment system is costly and unreliable. A dynamic model is thus needed in order to design model-based observers to estimate the exhaust gas oxygen concentrations at various locations. The oxygen-related reactions within a DOC and a DPF are investigated in this study. A lumped-parameter, control-oriented DOC-DPF oxygen concentration dynamic model was developed by a multi-objective optimization method and validated with experimental data obtained on a medium-duty Diesel engine equipped with full aftertreatment systems. Experimental results show that the model can well capture the oxygen dynamics across the Diesel engine aftertreatment systems.