Analysis of TWC 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 a WLTC 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 reductions with CO, C₃H₆ and H₂, steam reforming, water-gas shift and bulk ceria as well as surface ceria reactions). The reactions have been parameterized in order to best approximate the measurements.

Based on the reactions taken into account, the real vehicle emissions can be predicted with good accuracy. The simulations show that the cycle emissions comprise mainly 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 as well as surface ceria reactions for CO and THC. NO reduction during cold start is due to reaction with CO as well as due to surface ceria. During warm engine operation, 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 CO peaks and are also due to lack of oxygen and depleted CeO₂. NO transient break-throughs occur when engine-out NO sharply increases, and the reactions with CO and ceria are not sufficient.

Further analysis focused in highlighting the effects of variations of Lambda and precious metal content on reaction emissions and mechanisms.