Thomas Hauber

Three-Dimensional Simulation of the Transient Behavior of a Three-Way Catalytic Converter

The ultimate goal in the numerical simulation of automotive catalytic converters is the prediction of exhaust gas emissions as function of time for varying inlet conditions, i.e. the simulation of a driving cycle. Such a simulation must include the calculation of the transient three-dimensional temperature-field of the monolithic solid structure of the converter, which results from a complex interaction between a variety of physical and chemical processes such as the gaseous flow field through the monolith channels, the catalytic reactions, gaseous and solid heat transport, and heat transfer to the ambience. This paper will discuss the application of the newly developed CFD-code DETCHEM MONOLITH for the numerical simulation of the transient behavior of three-way catalytic converters that have a monolithic structure. The code combines the two-dimensional simulations of the reactive flows in a representative number of monolith channels with a transient simulation of the three-dimensional temperature field of the solid structure of the converter including insulation and canning. The chemical reactions are modeled by a multi-step heterogeneous reaction mechanism, which is based on the elementary processes on the platinum and rhodium catalysts used. The integration over the chemical conversion in the single channels leads to the total conversion in the converter as function of time. This paper presents a numerical simulation of the startup phase of an automotive catalytic converter for temporally varying inlet conditions. The variation of the temperature distribution in the solid structure and in the single channels as well as the species profiles are described. The numerically predicted time-dependent conversion of the combustion pollutants is compared with experimental data. The potentials and limitations of the models and computational tools are discussed.

Influence of Physical and Chemical Parameters on the Conversion Rate of a Catalytic Converter: A Numerical Simulation Study

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 parameters. 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 mechanism 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 simulated as a function of temperature. The numerically predicted conversion data are compared with experimentally measured data. The simulation further reveals the coupling between chemical reactions and transport processes within the monolithic channel.