Influences of exhaust gas temperature and flow rate on optimal catalyst activity profiles

This paper presents an optimization of an axial catalyst distribution for the two types of optimal axial catalyst distributions: continuous exponential and discrete two-zone, to enhance the light-off of a catalytic converter with a fixed amount of a catalyst. The influences of exhaust gas temperature and mass flow rate on the two types of optimal active component distribution profiles are identified and hence an optimum value for each of the operating conditions is quantitatively established. The catalyst surface area of the optimal distribution in the upstream section is greater, and in the downstream is lower than that of the uniform distribution. As an inlet exhaust gas temperature becomes lower than the catalyst light-off temperature, i.e., about 600 K, the catalyst surface area of the optimal distribution at the monolith inlet increases greatly to attain high reaction rates at the monolith entrance. In contrast, at temperatures above 600 K, it decreases slightly and hence its variation becomes negligibly small, as compared to the variation of the inlet gas temperature. The catalyst surface area at the monolith entrance decreases gradually with the increasing mass flow rate at gas temperatures above 550 K.