The Effect of Different Ageing Conditions on Spatial Variations in Emissions Across the Radius of a Close-coupled After-treatment System

Using local emissions measurements immediately downstream of a close-coupled catalyst, spatial variations in emissions have been analysed for close-coupled catalysts with different ageing histories. Comparison of the radial emissions profiles between a uniformly-aged (oven-aged) catalyst and two vehicle-aged parts suggests that the vehicle-aged parts have substantial variations in catalyst damage across the radius of the catalyst. The radial variations in damage were confirmed by bench reactor and post-mortem studies. The radial catalyst damage profiles inferred from engine-based evaluations of vehicle aged catalysts show broad correlation with high flow areas identified by CFD predictions and high temperature regions as measured during engine tests. Assessment of the results obtained from CFD analyses, engine-based evaluations, bench reactor evaluations and post-mortem suggests that flow non-uniformity creates high thermal gradients, leading to localised damage of the brick, thus degrading overall catalyst performance.