A new strategy for improving the warm-up performance of a light-off auto-catalyst for reducing cold-start emissions

Abstract

Light-off catalysts are often used to minimize cold-start emissions. The improved coldstart performance of light-off catalysts (LOCs) needs the optimal design in terms of flow distribution, geometric surface areas (GSA), precious metal (PM) loading, cell density and space velocity (SV). In this study, these influential factors are numerically investigated using an integrated numerical technique by considering not only the three-dimensional fluid flow but also the heat and mass transfer with chemical reactions. The present results indicate that uneven catalyst loading by depositing highly active catalyst materials upstream of the monolith is beneficial during the warm-up period, but its effect is severely deteriorated when the SV is above 100 000 h-1. To maximize light-off performance, this study suggests that: (a) the LOC be designed as a double-substrate type; (b) a substrate with high GSA and high PM loading at the face be placed at the front; (c) the cell density of the rear monolith be lower to reduce the pressure drop. In this paper, some initial results towards a new strategy of dual substrates are also reported to shorten the light-off time and improve conversion efficiency during warm-up. The proposed approach was very effective in reducing back pressure and cold-start emissions during the early seconds of engine operation.