Research Approach for Aging and Evaluating Diesel Lean-NOx Catalysts

The goal of the Diesel Emissions Control-Sulfur Effects (DECSE) program was to determine the impact of diesel fuel sulfur levels on emissions control devices that could lower emissions of oxides of nitrogen (NO_X) and particulate matter (PM) from on-highway trucks and buses. West Virginia University (WVU) performed evaluations of lean-NOx catalysts to determine the effects of fuel sulfur content on emissions reduction efficiency and catalyst durability in the first 250 hours of operation. A Cummins ISM370 engine (10.8 liter, 370 horsepower), typical of heavy -duty truck applications, was utilized to evaluate high-temperature lean-NO_X catalyst while a Navistar T444E (7.3 liter, 210 horsepower), typical of medium-duty applications, was used to evaluate low-temperature catalyst. Catalysts were evaluated periodically during the first 250 hours of exposure to exhaust from engines operated on 3ppm, 30ppm, 150ppm and 350ppm sulfur content diesel fuel. Lean-NO_X catalysts require the injection of hydrocarbons (diesel fuel) upstream of the catalyst to promote NO_X reduction. Prior to the catalyst aging experiments, the hydrocarbon (HC) reductant injection rate was optimized to yield significant NO_X reduction while controlling HC slippage. The low temperature lean-NO_X catalysts showed an average 15% NO_X reduction efficiency accompanied by an increase in HC emissions of 40% to 15 times. No clear effects on PM emissions were observed except for 350ppm fuel at 250 aging hours where PM emissions increased by 3.3 times. The increase of PM can be attributed to sulfate (SO₄). The high temperature catalysts had an average reduction efficiency of 11% for NO_X, an increase in HC emissions of 1-8.5 times and an increase in PM emissions after 250 aging hours.