Vehicle Comparison of Advanced Three-Way Catalysts and Hydrocarbon Trap Catalysts

FTP hydrocarbon emissions were measured on a sport utility vehicle comparing two catalyst systems. One system consisted of a close-coupled three-way catalyst and an underbody catalyst-only version of a hydrocarbon trap catalyst. The other system consisted of the same closed-coupled catalyst and underbody hydrocarbon trap catalysts. Thus, these systems compared a non-hydrocarbon trap system and a hydrocarbon trap catalyst system. Fresh and 50-hour aged testing showed that the hydrocarbon emissions were approximately 10% lower for the hydrocarbon trap catalyst system. When an air pump was used to inject air into the exhaust system, the hydrocarbon emissions of the hydrocarbon trap catalyst system were approximately 20% lower than the non-trap system. Hydrocarbon speciation demonstrated that the magnitude of the benefit of the hydrocarbon trap catalyst system was related to the characterization of the blend of hydrocarbon species in the exhaust after the close-coupled catalysts.