Fuel Sulfur Effect on Membrane Coated Diesel Particulate Filter

The diesel particulate filter (DPF), in conjunction with fuel reformulation technologies such as ultralow sulfur fuel or Fischer-Tropsch diesel, represents a promising solution for reducing particulate emissions. In this work, membrane-coated and conventional uncoated SiC diesel particulate filters were tested on a 4-cylinder Volkswagen TDI diesel engine under four different engine load conditions at constant engine speed. Di-tert-butyl-sulfide was added to the base fuel to increase the sulfur content from 39 ppm to approximately 300 PPM. Gaseous and particulate mass emission measurements, as well as, PM morphology and composition have been used to address how engine-out and post-DPF emissions and post-oxidation catalyst emissions change with increasing fuel sulfur content. The influence of fuel sulfur on emissions was compared for the membrane coated and uncoated SiC filter using the same diesel oxidation catalyst (DOC) located downstream of the DPF.

With the base fuel (39 ppm), the membrane coated filter shows lower PM emissions and higher PM filtration efficiency compared to the uncoated filter during the initial filling stage with a slight penalty in fuel consumption. Fuel sulfur had no effect on PM reduction efficiencies, with only a small increase in the soot+sulfate (i.e., insoluble) fraction and no change in the soluble organic fraction (SOF) of the PM mass. Particulate morphology, as seen by transmission electron microscopy (TEM), shows that the uncoated filter passes agglomerated particulate structures similar to the engine-out particles until a filter cake of PM is present. However, the membrane coated filter only allows small particles to pass at all times because the membrane coating provides a higher filtration efficiency.