Trends in Diesel Fuel Sulfur Regulations

摘要

Diesel engines emit particulate matter (PM) in the sub-micron range, which has been shown to cause respiratory ailaments with potentially cancer-causing consequences. Principal elements of PM include carbon (soot), soluble organic fraction (SOF), and sulfates. SOF consists of condensed aromatic compounds resulting from the incomplete combustion of diesel fuel. The oxidizing envioronment of the combustion process converts most of the indigeneous sulfur into a mixture of sulfur dioxide and sulfur trioide (SO_x). Some of the diesel sulfur, however, will form hydracted sulfates which become part of the total PM. The extent of sulfate-PM is an incentive to reduce fuel sulfur as part of the overall stragegy to reduce total PM emissions. For exaple, reducing sulfur from 500 ppm to 30 ppm has been predicted to reudce PM emissions by 9-12% for heavy-duty engines (1). Oxidation catalysts have been shown to be effective to reduce the SOF fraction of PM but countering this beneficial effect, oxidation can also increase suflate forma.tion