An experimental study on aging effects of the air–fuel ratio swing on modern gasoline three-way catalysts

Abstract

Today’s governmental legislations require region specific emission standards for passenger vehicles. Continuously increasing legal requirements demand the development of more complex exhaust gas after treatment systems to further reduce harmful gases like carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO_x). Due to specific load profiles and other boundary conditions, the efficiency of the aftertreatment system declines over lifecycle, so that the emissions might increase. Consequently, the durability of the system becomes a critical design parameter with upcoming legislation demanding emissions stability over the vehicle life cycle. Within this publication, catalyst aging effects due to air–fuel ratio (AFR) swing are analyzed experimentally. To create catalyst aging conditions, a modern eight-cylinder turbocharged engine was modified and specific aging cycles with a variation of AFR swing amplitude and frequency were conducted. Light-off curves were used to depict the negative impact of the AFR swing on the aging catalyst systems. A higher swing frequency resulted in an increased temperature amplitude within the entrance area of the catalyst, while an elevated amplitude lead to more exothermic heat release and stronger aging over the complete catalyst, as visualized via conversion maps. A theoretical calculation of thermal loads by Arrhenius equation supports the results and indicates the direction of supplementary experimental approaches.