Effect of oxidation catalysts on diesel soot particles

The effect of a conventional oxidation catalyst and a novel particle oxidation catalyst (POC) on diesel particles is studied using identical methodology. Regulated particulate matter emission measurement is followed by analyzing soluble organic fraction. In addition, size distributions are measured using a partial flow sampling system with a thermodenuder as an option. A parallel ELPI-SMPS method is used to study the particle effective density and, further, the mass. Tests are conducted using a heavy duty diesel engine with a very low sulfur fuel. A decrease in particle mass was observed when using a catalyst. When using a conventional catalyst the decrease was attributed to the decrease of soluble organic fraction, while using POC the nonsoluble fraction was also found to decrease, by 8-38%. This observation is confirmed by particle number measurement, and POC was found to decrease the dry particle number concentration measured downstream of a thermodenuder by 13-28%. Further particle structure analysis indicated lower density values when using conventional catalyst or POC. The physical size of the particles was not changed noticeably over either catalystsimplying the soluble organic fraction was condensed onto the soot, filling the voids in the porous structure of soot agglomerates, when no catalyst is used.