CFD-MODELING OF EXHAUST AFTERTREATMENT SYSTEMS FOR AUTOMOTIVE APPLICATIONS THE EFFECT OF FLOW DISTRIBUTION AND MASS TRANSFER

摘要

Computational Fluid Dynamics (CFD) is a powerful tool to make three dimensional simulations for exhaust systems with catalytic converters, which have to fulfil even tighter regulations concerning emissions from the vehicles. Several design parameters such as pressure drop of the system, flow distribution in the converter, temperatures and overall conversion of emissions in the converter can be obtained from the three dimensional solution. However, several important physical and chemical processes involved in a catalytic aftertreatment system can not be resolved directly through computational fluid dynamics, but must be introduced as empirical models. The model presented in this paper deals with the most important parameters involved in a catalytic converter such as pressure drop, mass transfer and chemical reactions in the monolithic substrate, and the mathematical models needed for a successfully implementation in a CFD-code. The model, which has been implemented on the exhaust system of a Saab 9-5 2.3 litre turbo engine, is validated against experimental data from engine bench measurements. Furthermore, the effect of flow distribution and mass transfer on the conversion efficiency is studied using the model. The model can successfully predict flow dependent parameters such as pressure drop, flow distribution and location of light-off in the converter, while more accurate models are needed for reaction kinetics and mass and heat transfer.