Assessment of diagnostic approaches for NOx storage catalysts in view of future emission & OBD legislations

On top of the increasing stringency of emission limits, robust monitoring of the health of emission control devices is becoming an additional key challenge for powertrain systems.
This paper aims to evaluate diagnostic monitoring approaches for lean NOx traps. A NOx storage catalyst or lean NOx trap (LNT) absorbs and stores emissions of oxides of nitrogen (NOx) during lean operation. When saturated with NOx, a rich phase in the order of a few seconds is required to release and reduce the stored NOx into non-polluting components, mainly nitrogen, carbon dioxide, and water vapor.
Two different monitoring methods are being assessed on their ability to robustly separate LNT aging states and to respect legislative requirements. A first method uses lambda sensors and evaluates the reductants presence against a threshold model. In a second approach a kinetic reference model compares the predicted NOx slip with the downstream NOx sensor measurement. Furthermore, the paper outlines the limitations of both approaches and the complexity of a kinetic model based diagnostics.