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

The effects of “periodic operation (variations of both A/F modulation width and their frequency)” on the activities of fresh and aged Pt/Rh catalysts were systematically evaluated on engine dynamometer in terms of A/F and cold-start performance. A/F modulation width and its frequency were varied from ±2 to ±10% A/F 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 NOx emission on the aged catalyst was confirmed, although a medium effect was appeared on the fresh catalyst.