Durability Assessment of Diesel Cold Start Concept (dCSC) Technologies

摘要

The phase-in of US EPA Tier 3 and California LEV III emission standards require further reduction of tailpipe criteria pollutants from automobiles. At the same time, the mandate for reducing Green House Gas (GHG) emissions continuously lowers the exhaust temperature. Both regulations pose significant challenges to emission control catalyst technologies, especially for cold start emissions. The recently developed diesel cold start concept technology (dCSC) shows promising results. It stores NO_x and HC during the cold start period until the downstream catalytic components reach their operating temperatures, when the stored NO_x/HC are subsequently released and converted. The technology also has oxidation functions built in and acts as a diesel oxidation catalyst under normal operating conditions. In a US DOE funded project, the diesel cold start concept technology enabled a high fuel efficiency vehicle to achieve emissions targets well below the SULEV30 emission standards. In this study, detailed lab assessments of a development diesel cold start concept catalyst were carried out with emphasis on its long-term durability. The catalyst exhibits high NO_x/HC storage capacities with high trapping efficiency in the temperature range of 80 to 200°C. The majority of NO_x storage sites can be regenerated at temperatures above 250°C. The catalyst is thermally durable after 750°C/100 h/10% H_2O hydrothermal aging, although a noticeable decline of NO_x storage capacity is observed after 10 hours aging at 850°C, or after exposure to a rich atmosphere. The catalyst also has good sulfur tolerance, maintaining high NO_x storage capacity even after a 2 g S/L catalyst of sulfur exposure. The long-term durability of the catalyst to hydrothermal aging and to repetitive sulfation/desulfation cyclic aging is also demonstrated on engine/vehicle evaluations. An engine aged catalyst that represents its end of useful life shows clear advantages for cold start NO_x/CO/HC emission control on a light-duty diesel truck.