Effects of Oil-Derived Contaminants on Emissions from TWC-Equipped Vehicles

Advances in fuel control strategy, emission system architecture, and catalyst technology have led to dramatic decreases in exhaust emissions in recent years. To continue this trend, especially at high mileages, the impact of engine oil derived contaminants will need to be minimized. In this study, the deactivating effects of oil-derived contaminants on advanced catalyst technologies was assessed using an oxalic acid washing technique to remove phosphorus and other oil-derived contaminants from fleet-aged automotive three-way exhaust catalysts. Acid washing removed most of the phosphorus on the catalyst (chief poison associated with decomposition of the engine oil antiwear additive ZDDP) without significantly affecting other catalyst properties. Catalysts from eight high-mileage vehicles were analyzed, representing four vehicle families. Averages taken over all of the catalyst systems showed substantial decreases in FTP emissions resulting from acid washing: 42% for HC, 20% for CO, and 35% for NOx. A measure of light-off performance, termed inefficiency-seconds, was found to be a convenient and accurate method for quantifying the impact of oil contaminants on catalyst activity. The results suggest that no more than 2-5 g P/L_cat can be tolerated on the front catalyst bricks of vehicles targeted for ULEV emission standards.