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 pro??cesses 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 start-up 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.