1997-02-24

Technologies for Reducing Cold-Start Emissions of V6 ULEVs 971022

New technologies are needed to reduce cold-start emissions in order to meet the more stringent regulations that will go into effect in Europe (EC2000 or EC2005) and in California (ULEV), especially for larger engines such as 6- and 8-cylinder units. One new technology in this regard is the electrically heated catalyst (EHC). However, the use of EHCs alone is not sufficient to achieve the necessary reduction in emissions.This paper discusses techniques for effectively combining the elements of an EHC system, including the introduction of secondary air into the exhaust, improved control of the air/fuel ratio, and an electric power supply method for EHCs. It is shown that it is more effective to promote exothermic reactions in the exhaust manifold than at the EHC. A suitable method for this purpose is to introduce secondary air into the exhaust near the exhaust valves. Moreover, an effective way to increase these reactions is to apply a richer air/fuel ratio, especially during the cold-start period. Electric power for EHCs can be supplied from the alternator or from the battery. With the alternator-power supply system, it has been found that the volume of exhaust gas increases as the alternator load rises, which has the disadvantage of lowering the rate of exothermic reactions. Supplying electric power from the battery is therefore a better approach from the standpoint of reducing exhaust emissions.

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