Thermal Response of Close-Coupled Catalysts During Light-Off

A case study of a close-coupled catalyst subjected to exhaust gas conditions typical for a modern engine warm-up phase is studied using a time-efficient 2-dimensional modeling approach. The flow distribution at catalyst inlet is affected by the downstream flow resistance, which is in turn a function of catalyst temperature field. Unlike traditional CFD approaches, the presented model focuses on this interesting coupling between the problems of flow distribution and catalyst thermal response. The results are expressed in terms of time-dependent velocity and temperature distribution as well as conversion efficiency. After a basic understanding of the phenomena, a parametric analysis is performed to assess the significance of various design parameters affecting the cold start performance of close-coupled catalysts. It is shown that the detrimental effect of flow uniformity on light-off is associated to the non-uniform ageing. In fresh catalysts or uniformly aged catalysts, the flow maldistribution is not expected to affect light-off during typical (low flow rate) warm-up conditions. The effect of catalyst insulation and mantle is also studied.