A Modelling Approach to the Design Optimization of Catalytic Converters of I.C. Engines

In this paper, a modelling approach to the design optimization of catalytic converters is presented. The first step of the optimization is the model-assisted sizing of catalysts. For a given inlet exhaust condition, a semi-empirical, experimentally calibrated, 0-D steady state catalyst model is employed to sort through a data base of catalysts under given restraints, yielding few successful candidates. Following this screening process, a 1-D transient plug-flow catalyst model is used to analyze the species concentrations and the temperature variation across the catalyst. The second step deals with the flow optimization of the catalyst converter under the given geometric restraints. A commercially available CFD package is employed to simulate isothermal flow and to evaluate flow uniformity characteristics in the catalytic converter. The substrate is modelled as porous media, where viscous and initial resistances are specified via empirical formula. With the help of the CFD tool, the flow in the converter can be optimized using appropriate boundary layer control methods. In a specific example, the effects of perforated plate on the flow separation in a wide-angle diffuser are demonstrated. This paper also addresses the issue of flow resistance of perforated plates.