Analysis of TWC Operation Characteristics in a Euro6 Gasoline Light Duty Vehicle 2019-24-0162
A Euro6 gasoline light duty vehicle has been tested at the engine dynamometer and the emissions have been analyzed upstream and downstream the Three-Way-Catalyst (TWC) during the WLTP cycle. Catalyst simulations have been used for assessing the processes inside the catalytic converter using a reaction scheme based on 19 brutto reactions (Direct oxidation and reduction, selective catalytic re-ductions with CO, C3H6 and H2, steam reforming, water-gas shift and bulk Ceria as well as surface Ce-ria reactions). The reactions have been parametrized in order to best approximate the measurements.
Based on the reactions taken into account, the real vehicle emissions can be predicted with good accu-racy. The simulations show that the cycle emissions are comprising mainly by the cold start contribution as well as discrete emission break-through events during transients. During cold start no reactions are evident in the catalyst before the temperature of the gas entering the catalyst reaches 270°C. Following the light-off, prevailing reactions are direct oxidation for CO and direct oxidation as well as surface ceria reactions for THC. NO reduction during cold start is due to reaction with CO as well as due to surface ceria. CO break-throughs during transients are mainly due to lack of oxygen following short periods where the engine lambda drops below one and most of surface and bulk CeO2 has reacted to surface and bulk Ce2O3. Moreover in such incidents ceria is reacting with THC forming additional CO. THC break-throughs during transients are mostly simultaneous with the CO peaks and are also due to lack of oxygen and depleted CeO2. NO transient break-throughs occur when engine-out NO increases sharply and reactions with CO and Ceria are not sufficient to reduce all NO.
Further analysis focused in highlighting the effects of variations of Lambda, precious metal content and Oxygen Storage capacity.