CATALYTIC CONVERTER DESIGN FOR MINIMISATION OF COLD-START EMISSIONS

Abstract

Abstract 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. A result of practical significance is that the evolution and the steady-state value of the temperature of the exhaust gas stream at the monolith inlet do not affect significantly the form of The optimal distribution. 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. A converter with two-zones, each having a different but uniform catalyst loading is also examined. It is shown that such a design can closely approximate the optimal distribution. Finally, performance degradation due to sintering is shown to be more severe for The case of the uniform catalyst distribution.