Development of a New Oxygen Storage Model for SIMTWC

The high conversion efficiency required by the modern three-way catalyst (TWC) is dependent on oxygen storage material functionality and capacity. To successfully model a TWC, it is critical that the oxygen storage function in the catalyst be adequately represented. The original oxygen storage model (a simple “bucket” model) included in one of Ford's TWC models, SIMTWC, was developed for vehicle programs meeting LEV emission standards. Application of SIMTWC to test data from vehicles targeting more stringent emission standards, such as ULEV and PZEV, revealed limitations in the accuracy of the original bucket model. To address these limitations, an improved kinetic model of oxygen storage is being developed. This new model is more kinetically-detailed than the old model. Kinetic parameters, i.e., reaction constants and activation energies, are generated from laboratory flow reactor data with low frequency air-fuel ratio changes and validated using laboratory test data with high frequency air-fuel ratio fluctuations. Post-catalyst air-fuel ratio predictions are very close to actual measured values and demonstrate the model capability to handle air-fuel ratio switches typical of real vehicle control strategies.