Improvement of Engine Emissions Tower Three-Way Catalyst by the Periodic Operations

The effects of ''periodic operation (variations of both AF modulation width and their frequency)'' on the activities of fresh and aged PtRh catalysts were systematically evaluated on engine dynamometer in terms of AF and cold-start performance. AF modulation width and its frequency were varied from +-2 to +-10% AF and from 0.5 to 5 Hz, respectively. The periodic operation effects for both catalysts were the most preferable for diminishing THC emission and a little effect was obtained for CO emission. A remarkable improvement of NO/sub x/ emission on the aged catalyst was confirmed, although a medium effect was appeared on the fresh catalyst.