NOx trap showing better 'simulated' durability for both light-, heavy-duty applications

Diesel Fuel News, Sept 29, 2003

NOx Trap Showing Better 'Simulated' Durability For Both Light-, Heavy-Duty Applications: Researchers are using high-sulfur fuel to "simulate" and then extrapolate the effect of long-duration operation of ULSD on NOx trap durability, after repeated desulfations. This joint research project by EmeraChem, Cummins and Oak Ridge National Laboratory indicates that a twin-path NOx adsorber probably can survive repeated desulfurization cycles and still maintain high NOx efficiency over EPA-required "useful life" mileage (150,000 miles light-duty, 435,000 miles heavy-duty).

However, a light-duty version still has efficiency limitations for cold-start/low-temperature portions of duty cycle. On heavy-duty, researchers still have concerns about NOx efficiency at higher mileage, and about coverage of the entire exhaust temperature range. At today's level of technology development, "certification requirements for 2010 [0.2 g/bhp-hr NOx] will be difficult," EmeraChem researcher Jim Parks conceded here. Lube-oil components may be responsible for "significant degradation" of NOx catalyst efficiency, so researchers will investigate the mechanisms and performance impact. In tests to date, the researchers have loaded-up the NOx trap with fairly high-sulfur fuel (150-ppm) to accelerate sulfur aging. Then they desulfated the trap with near-zero sulfur (1-ppm) ultra-low sulfur diesel (ULSD). They're assuming that in the real world, a 15-ppm sulfur ULSD would be used for high-temp (500-550[degrees]C) desulfation every 1,000 miles on heavy-duty, for this proprietary NOx trap formulation that enables relatively lower-temperature desulfation. Hence 1,000 desulfurization iterations would represent the 1 million miles that heavy-duty truck customers have come to expect for "useful life." In this simulated aging scheme, >90% NOx reduction efficiency was maintained for 435,000 miles, but deterioration accelerated sharply after 800,000 miles, falling to about 75% efficiency by 1 million miles.