NOx adsorber performance in a light-duty diesel vehicle

Light-duty chassis dynamometer driving cycle tests were conducted on a Mercedes A170 diesel vehicle with various sulfur-level fuels and exhaust emission control systems. Triplicate runs of a modified light-duty federal test procedure (FTP), US06 cycle, and SCO3 cycle were conducted with each exhaust configuration and fuel. The fuels used in these experiments met the specifications of the fuels from the DECSE (Diesel Emission Control Sulfur Effects) program (1, 2, 3 and 4)¹. Ultra-low sulfur (3 ppm) diesel fuel was doped to 30 and 150 ppm sulfur so that all fuel properties except sulfur content would be the same. Although the Mercedes A170 vehicle is not certified for sale in the United States, its particulate matter (PM) and nitrogen oxide (NO_x) emissions in the as-tested condition were within the Environmental Protection Agency's Tier 1 full useful life standards with its OEM oxidation catalysts installed. Engine-out tests showed that the OEM catalysts reduce PM by 30-40%. There was very little effect of fuel sulfur on the performance of the OEM oxidation catalysts. With a replacement lightoff catalyst and NO_x adsorber (lean-NOx trap) installed, FTP NO _x emissions were reduced by more than 90% with 3 ppm fuel. Reductions of NO_x on the US06 and SC03 cycles were 89% and 96%, respectively. Following the evaluations with the ultra-low sulfur fuel, the catalyst system was poisoned with the equivalent of 3,000 miles on 30 ppm sulfur fuel, which reduced the system's effectiveness to 80% on the FTP, 66% on the US06, and 84% on the SC03.