Experimental and numerical analysis on the effect of adsorbed oxygen on the improvement of three-way catalysts purification performance by rich-lean lambda perturbation

High exhaust gas temperature thermally degrades catalysts, reduces oxygen storage capacity (OSC), and deteriorates three-way catalysts (TWC) purification. Possible solutions to reduce the degradation are enriching the air–fuel mixture and lowering gas temperature. Therefore, improving the degraded catalyst performance under low gas temperatures is essential. Synthetic exhaust flow reactor experiments are conducted to measure purification performance data of fresh and thermally aged catalysts under different temperatures and rich-lean perturbations. For the catalyst with OSC, the behavior of the decrease in conversion rate due to perturbation was spike-like, and the reduction in conversion rate was slower than for the catalyst without OSC. The data are also used to validate a TWC model accounting for surface reactions and OSC. The results show that the model can significantly improve the conversion rates under rich-lean perturbations. The optimal perturbation frequencies from 0.05 – 2.5 Hz can improve CO and NO conversion rates to over 99%. Also, even if the catalyst is thermally degraded, the purification performance can be improved by increasing the fluctuation in the oxygen coverage by, for example, introducing rich- lean lambda perturbation at low temperature. This was made clear by experiments that focused on oxygen coverage using a numerical calculation model reproducing the experimental results. This work can be used as a guideline to design efficient TWCs for next-generation hybridized vehicles.