2000-01-0211 Influence of Physical and Chemical Parameters on the Conversion Rate of a Catalytic Converter: A Numerical Simulation Study Joachim Braun, Thomas Hauber, Heike Többen and Peter Zacke J. Eberspächer GmbH & Co. Daniel Chatterjee, Olaf Deutschmann and Jürgen Warnatz University of Heidelberg Copyright © 1999 Society of Automotive Engineers, Inc. ABSTRACT Monolithic three-way catalysts are applied to reduce the emission of combustion engines. The design of such a catalytic converter is a complex process involving the optimization of different physical and chemical parame- ters. Simple properties such as length, cell densities or metal coverage of the catalysts influence the catalytic performance of the converter. Numerical simulation is used as an effective tool for the investigation of the catalytic properties of a catalytic converter and for the prediction of the performance of the catalyst. To attain this goal, a two-dimensional flow field description is coupled with a detailed chemical reaction model. In this paper, results of the simulation of a monolithic single channel are shown. In a first step, the steady state flow distribution was calculated by a two dimensional simulation model. Subsequently, the reaction mecha- nism of the chemical species in the exhaust gas was added to the simulation process. The performance of the catalyst was simulated under lean, nearly stoichiometric and rich conditions. For these characteristic conditions, the oxidation of propen and CO and the reduction of NO on a typical Pt/Rh coated three-way catalyst were simu- lated as a function of temperature. The numerically pre- dicted conversion data are compared with experimen- tally measured data. The simulation further reveals the coupling between chemical reactions and transport pro- cesses within the monolithic channel. INTRODUCTION Today three-way catalysts are used extensively to reduce the emissions of combustion engines. The majority of automotive catalytic converters have a mono- lithic structure, which is coated with an alumina wash- coat that supports the noble metal such as platinum, palladium and rhodium. These monoliths can be made of either ceramic or of metal. To achieve a large catalytic surface area, the substrates consist of numerous parallel channels with a diameter of approximately 1 mm. For the design of a catalytic converter, several chemical and physical properties of both the catalyst and the exhaust gas must be considered: • cell geometry (length and diameter of the channel, wall thickness), • species of noble metal and noble metal loading, • species of promotors, • temperature, velocity and chemical composition of the exhaust gas. The experimental characterization of the catalytic performance of the converter is time-consuming and requires a large experimental setup. Moreover, multiple experimental measurements should be made to ensure reproducibility. Numerical simulation offers an interesting alternate method for the investigation of the catalytic activity of a converter. This method is also efficient in analyzing the transient flow and thermal phenomena in the catalytic converter and may help to understand the complex interactions between the flow field and the catalytic surface chemistry. In recent years, several proposals were made for the numerical simulation of catalytic converters /1-6/. In most of these studies, a global model for the chemistry was used. This global model however neglects the various single reactions which occur on the surface. An alternate approach is the description of the chemical reactions by a set of elementary reaction steps. The reaction equa- tions of the elementary steps describe the reactions on a