The Impact of Lubricant and Fuel Derived Sulfur Species on Efficiency and Durability of Diesel NOx Adsorbers

Global emission legislations for diesel engines are becoming increasingly stringent. While the exhaust gas composition requirements for prior iterations of emission legislation could be met with improvements in the engine's combustion process, the next issue of European, North American and Japanese emission limits greater than 2005 will require more rigorous measures, mainly employment of exhaust gas aftertreatment systems. As a result, many American diesel OEMs are considering NOx adsorbers as a means to achieve 2007+ emission standards. Since the efficacy of a NOx adsorber over its lifetime is significantly affected by sulfur (“sulfur poisoning”), forthcoming reductions in diesel fuel sulfur (down to 15 ppm), have raised industry concerns regarding compatibility and possible poisoning effects of sulfur from the lubricant. Since relatively little is known about the interaction between lubricant derived sulfur and NOx adsorbers, a joint technical program was conducted using a Cummins 5.9L engine and NOx adsorbers supplied by Delphi. Fuel sulfur was kept constant (2ppm) while the effects of “high” (0.6%) and “ultra low” (0.003%) S containing lubricants were examined. Statistical analysis of the change in NOx conversion revealed that the loss in NOx conversion was proportional to and mainly dependent on the rate of total sulfur exposure, regardless of the sulfur source. In addition, the results of this study allow review of the effects of engine oil sulfur in perspective to the future EPA mandated ultra low sulfur diesel fuel. It should be noted that this work describes only initial sulfur poisoning studies and that no evaluations of NOx adsorber desulfations are addressed.