On the Effective Density and Fractal–Like Dimension of Diesel Soot Aggregates as a Function of Mobility Diameter

A new technique is proposed for the assessment of aggregate morphology based on combined information of aerodynamic and mobility size distributions. Instead of formulating a complex inverse problem having aggregate morphology as unknown, the actual problem is separated to two stages. The aerodynamic distribution is determined directly by the electric low pressure impactor (ELPI) data whereas the morphology is independently assessed by matching the distribution arises from ELPI and from scanning mobility particle sizer (SMPS). The advantage of this approach is that it can estimate different fractal dimension for different aggregate size. The approach is applied to soot aggregates from three different diesel engines. In all cases, a non-monotonic behavior of fractal dimension versus aggregate size is observed. In particular, the fractal dimension initially decreases and then increases (passing through a minimum) as the mobility diameter increases.