Use of Light-Off Catalysts to Meet the California LEV/ULEV Standards

Hydrocarbon conversion across emission control catalysts is a strong function of inlet temperature. The bulk of unconverted hydrocarbon emissions arises in Bag 1 of the FTP-75 cycle before the emission control system goes closed-loop. A general strategy for improving converter hydrocarbon efficiency is to heat up the catalyst early in Bag 1. One strategy for doing this is to place a small catalytic converter near the engine manifold. This approach to hydrocarbon control is well established and represents a production feasible method. This paper explores the use of close-coupled catalysts in conjunction with conventional underfloor converters for achieving the California low emission vehicle standards. The paper identifies catalytic formulations for both converters that optimize emission system performance. The benefits of double wall exhaust pipe connecting the two converters and thin walled substrate for the light-off catalyst were also studied.