A Comparison of Steady, Pulsating Flow Measurements and CFD Simulations in Close Coupled Catalysts

Performance improvements of automotive catalytic converters can be achieved by improving the flow distribution of exhaust gases within the substrate. The flow distribution is often assumed to be adequately described by measurements obtained from steady flow rigs. An experimental study was carried out to characterise the flow distribution through the substrate of a close-coupled catalytic converter for both steady and pulsating conditions on a flow rig and on a motored engine. Computational fluid dynamic (CFD) simulations were also performed. On the flow rig, the flow from each port was activated separately discharging air to different regions of the substrate. This resulted in a high degree of flow maldistribution. For steady flow maldistribution increased with Reynolds number. Pulsating the flow resulted in a reduction in flow maldistribution. Different flow distributions were observed on the motored engine when compared to composite maps derived from the rig. For the engine study significantly more flow activity was observed at the periphery of the substrate, each port contributing to the net flow. The results suggest that strong port interactions occur. CFD simulations showed qualitative agreement with measurements but underestimated the flow maldistribution.