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Numerical simulations are increasingly assisting research and development in the field of emission control of automotive vehicles. Our work focuses on the prediction of the tail-pipe emissions, based on a numerical simulation of the automotive catalytic converter. Besides the prediction of the tail-pipe emissions, an understanding of the processes occurring inside a monolithic catalytic converter implies new opportunities for the design of the optimum exhaust gas system. In this paper, we present a three-dimensional transient numerical study of the influence of the velocity distribution in front of the inlet face on the thermal behavior of the monolith during the light-off of a 3-way catalytic converter. The differences in the thermal and chemical behavior due to the shape of the velocity distribution are discussed. The recently developed code DETCHEMMONOLITH /1/ is used for the numerical simulation.

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 DETCHEMMONOLITH for the numerical simulation of the transient behavior of three-way catalytic converters that have a monolithic structure.

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.

Today most catalytic converter designs have monolith-type substrates. Many of these designs use more than one monolith, due to different catalyst loadings or constraints on the manufacturing or coating of long monoliths. There is usually an open space between the monoliths. The flow distribution in the catalytic converter depends on the cone geometry of the catalytic converter, the space between the monoliths and their design. A connection between the flow distribution and the high conversion rate and the good long term stability is supposed. This paper presents the results of a study of the influence of space between monoliths, cone geometry and monolith length, on flow distribution, catalytic converter conversion rate and backpressure. The conversion rates for HC, CO and NOx at different engine load levels have been investigated.