Analysis of fractal particles from diesel exhaust using a scanning-mobility particle sizer and laser-induced incandescence

The emission regulations for diesel particulate matter (PM) are becoming increasingly strict. The focus of regulations is turning to reducing the number of nanosized particles as well as the total mass. A more precise measurement technique for particle numbers and mass must be developed to meet these new regulations. In this study, a new method for estimating the mass weighted size distribution of diesel PM was investigated by measuring the size of primary particles and the number concentration distribution of particle aggregates. Time-resolved laser-induced incandescence was used for primary particle size measurement and a scanning-mobility particle sizer was used to quantify the number concentration of aggregates. The results from these two conventional measurement techniques were combined using fractal analysis formulas to relate the electrical mobility diameter, the number of primary particles per aggregate, primary particle size, and fractal dimension. This method, applied to single-cylinder diesel engine exhaust with various engine loads and injection pressures, successfully estimated the mass weighted size distribution of particle aggregates. The procedure is very simple and the estimations are comparable with those based on effective density, making this method a useful and reliable tool for estimating mass weighted size distribution of fractal particles such as diesel PM.