Emission Reduction Technologies for Turbocharged Engines 1999-01-3629
It is projected that compliance with Japanese new exhaust emission regulations set to be enforced in 2000 year will be difficult for turbocharged engines with conventional technologies. This is mainly because of the delay in catalyst lightoff at engine start due to the lower exhaust gas temperature of turbocharged engines compared with that of their naturally aspirated counterparts. Compliance will be particularly difficult for V-6 engines on account of the large heat mass of the exhaust system, resulting in a slower temperature rise.
Previously, improvement of hydrocarbon (HC) conversion rates following engine start depended solely on the low-temperature characteristic of the catalyst. The catalyst system described here adopts a completely new mechanism that traps HCs before the catalyst lights off and then desorbs them for conversion after the engine warms up. Implementation of this system overcomes the limitation on low-temperature catalyst activity, making it possible to reduce HC emissions from the time of engine start.
Moreover, the close-coupled catalyst features a high cell density, ultra-thin metal substrate incorporating a new bonding method called diffused bonding. The combination of this 30-μm-thick metal substrate with 600 cells and the above-mentioned HC trap significantly reduces HC emissions. This system makes it possible to achieve low emission levels for turbocharged engines, which has so far been difficult to accomplish. The adoption of these new technologies enables a turbocharged V-6 engine to meet Japanese 2000 exhaust emission standards.