FRACTAL AND PROJECTED STRUCTURE PROPERTIES OF SOOT AGGREGATES

The structure of soot aggregates was investigated, emphasizing the fra ctal properties as well as the relationships between the properties of actual and projected soot images. This information was developed by c onsidering numerically simulated soot aggregates based on cluster-clus ter aggregation as well as measured soot aggregates based on thermopho retic sampling and analysis by transmission electron microscopy (TEM) of soot for a variety of fuels (acetylene, propylene, ethylene, and pr opane) and both laminar and turbulent diffusion flame conditions. It w as found that soot aggregate fractal properties are relatively indepen dent of fuel type and flame condition, yielding a fractal dimension of 1.82 and a fractal prefactor of 8.5, with experimental uncertainties (95% confidence) of 0.08 and 0.5, respectively. Relationships between the actual and projected structure properties of soot, e.g., between t he number of primary particles and the projected area and between the radius of gyration of an aggregate and its projected image, also are r elatively independent of fuel type and flame condition.