A unified approach for modeling three-way catalytic converters and NOx traps with a minimum set of tunable parameters

Abstract

The demanding legislation for vehicle emissions pushes the automotive industry to the commercialization of advanced exhaust systems. The careful design of each aftertreatment device fitted in exhaust line and the interactions with the engine management, makes modelling an important part of systems engineering for these applications. Almost all catalytic converter models that are found in the literature use tunable parameters which typically address the kinetic terms of chemical reactions. A great effort has been given to the definition of complex reaction schemes and mechanistic description of them in-vitro, in order to assist the advanced design of catalytic washcoats and explain their complex chemistry. This paper presents a systematic effort towards the modelling of advanced commercial exhaust treatment systems, using a unified approach for the different devices. The model used in this work describes the catalytic processes with global reactions, using apparent Arrhenius type rate expressions with L-H kinetics. The model is used to predict transient performance of commercial catalytic converters under legislated test conditions. During these tests the existing uncertainties and intrinsic variations of engine and catalyst operation make the robustness and flexibility of the model prominent targets. Comparison of computed and measured second-by-second emissions demonstrate a high level of modelling accuracy, adequate to fit the behavior of advanced commercial applications of three-way catalytic converters and NOx traps, using a minimum set of 3 tunable parameters for each device. Copyright © 2007 The Berkeley Electronic Press. All rights reserved.