Optimal axial catalyst distribution in monolithic catalytic converters for minimisation of cold-start emissions

The axial catalyst distribution in a monolithic converter that minimises cold-start pollutant emissions is investigated numerically, under the constraint of fixed total catalyst surface area Various warm-up mechanisms can be present during the transient period The catalyst distribution affects greatly which mechanisms prevail. For the optimal distribution, a large amount of catalyst is required in the upstream section of the monolith. This ensures that the hot spot is kept at the monolith inlet throughout the warm-up period, and hence heat transfer by convection dominates, As a result, a significant reduction of cold-start emissions can be achieved. Even though the local catalyst surface area of the optimal distribution in the downstream section of the converter is reduced as compared to the uniform distribution, steady-state performance is not adversely affected.