Computational Modeling of Diesel NOx Trap Desulfation

The major challenge in diesel NO_x aftertreatment systems using NO_x adsorbers is their susceptibility to sulfur poisoning. A new computational model has been developed for the thermal management of NO_x adsorber desulfation and describes the exothermic reaction mechanisms on the catalyst surface in the diesel NO_x trap. Sulfur, which is present in diesel fuel, adsorbs as sulfates and accumulates at the same adsorption sites as NO_x, therefore inhibiting the ability of the catalyst to adsorb NO_x. Typically, a high surface temperature above 650 °C is required to release sulfur rapidly from the catalyst [1]. Since the peak temperatures of light-duty diesel engine exhaust are usually below 400 °C, additional heat is required to remove the sulfur. This report describes a new mathematical model that employs Navier-Stokes equations coupled with species transportation equations and exothermic chemical reactions. These reactions on the NO_x trap catalyst surface are directly coupled with the energy equation to predict mass and heat transfer between the gas phase and the catalyst. This computational model agrees well with gas bench results [1] for both gas temperatures and species mole fractions. In the present study, we have focused on steady state phenomena to validate the physical models and it's numerical accuracy.