Oxygen storage dominated three-way catalyst modeling for fresh catalysts

Abstract

Meeting future legislations for the emissions of spark-ignition engines requires the development of efficient three-way catalyst (TWC) models. These models can both be employed for online catalyst control as well as model-based development of control and on-board diagnosis (OBD) strategies. In this paper we present such a model that aims at capturing transient TWC dynamics of fresh catalysts at elevated temperatures. Applying a parameter subset selection strategy, we demonstrate that solely taking into account the dynamics of oxygen storage and release is sufficient for this purpose and reactions associated with processes taking place on the platinum-group metals do not have to be modeled explicitly. The one-dimensional single channel model lumps the exhaust gas species into two pseudo components, one being able to oxidize and one being able to reduce the oxygen storage material. The respective reaction kinetics are considered reversible with non-linear functions depending on the oxidation state of the material being put in the center of focus. Model validation is carried out using experimental data from an isothermal synthetic gas test bench. The applied feed gas composition closely resembles real exhaust conditions under dynamic operation. By employing local parameter sensitivity and identifiability analysis and investigating the differences between a total of five fresh catalysts from different commercial suppliers, we propose a set of only five parameters that can be used to accurately model oxygen storage and release dynamics under isothermal conditions. The results emphasize the importance of accounting for oxygen storage from water as well as the need of using a spatially distributed model. Apart from the above mentioned applications, the model is shown to be suitable for fast catalyst screening and characterization.