Diesel Particulate Emissions of Passenger Cars - New Insights into Structural Changes During the Process of Exhaust Aftertreatment Using Diesel Oxidation Catalysts 980196

Diesel particulate mass emissions and their corresponding size distributions have been investigated on a diesel passenger car at steady state conditions using standard filters and a cascade impactor. These tests have been carried out at two different engine operating conditions (2100 rpm, 2.7 and 13.3 kW, respectively) corresponding to low and high exhaust gas temperatures. Two diesel fuels differing in their sulfur content (150 ppm and 2500 ppm S) have been used for these investigations.

The particulate size distribution after diesel oxidation catalyst was found to be affected by the sulfur content of the diesel fuel and by the exhaust gas temperature. Interpretations of these results on a mechanistic basis are given.

The diesel particulate emission studies have been extended to dynamic vehicle tests. The structural changes of the particulates using a single and a double-brick catalyst system have been determined during the MVEG-A test in order to identify the influence of catalyst volume. The development of the diesel particulates (size distribution and composition) along the exhaust system have also been studied. The particulate size distribution seems to be shifted to smaller particulate sizes with increasing catalyst volume. However, the primary particles remain unchanged by the diesel oxidation catalyst. Therefore, the apparent shift to smaller particulate sizes is explained by the increased removal of the Soluble Organic Fraction with higher catalyst volume. The adhesive responsible for an enlargement of the particulates is missing and therefore smaller particulate sizes have been observed. Hydrocarbon and sulfat condensation seems to be the key parameters responsibile for changes in particulate sizes. Experimental results therefore must be interpreted carefully, because they are affected strongly by the experimental arrangement. A detailed discussion of the effects of analytical conditions (e.g. the dilution ratio) on the observed results is given.