Modeling of OSC Function over Three-way Catalyst

Three way catalysts (TWC) contain Oxygen Storage Component (OSC) materials to enhance HC, CO oxidation and NOx reduction performance under standard operating conditions where there is rapid perturbation of the air-to-fuel ratio (A/F). The OSC function is required to storage and to release oxygen, however the optimum storage capacity and release rate to maximize HC, CO and NOx conversion varies as a function of engine operating conditions, such as A/F perturbation frequency, amplitude and temperature. At the same time, it is necessary for the vehicle on board diagnostics (OBD) systems to monitor that the catalyst OSC is functioning correctly. Detailed understanding of how OSC characteristics can simultaneously match gas performance and OBD functionality are not well known.

In this study, modeling of the OSC function was attempted by considering chemical functions to be analogous to that in an equivalent electrical circuit, having components of resistance and capacitance. Here the oxygen storage function of the OSC material will be considered as a capacitance and the oxygen and/or electron mobility in the OSC will be considered as a resistance. The characteristics of oxygen storage and release will be analyzed in the same manner as charge and discharge of an equivalent CR-circuit.