Measuring the fractal dimension of diesel soot agglomerates by fractional Brownian motion processor

This work explores the application of fractional Brownian motion (FBM) analysis to SEM micrographs of soot aggregates exhausted by a model dynamometer. By directly quantifying the surface texture of fractal-like aggregates to extract their Hurst coefficients (H), the FBM analysis was successful in parameterizing fractal dimension (Df) values, from which the relative aggregate structure variables could easily be determined. For two microscopic magnification scales (×50,000 and ×105), the soot aggregate Df fell in the range of 1.6–1.7. The experimental results closely agreed with the main conclusions derived from previous studies. An alternative approach is to clarify the impact of image properties on Df measurements due to digital image processing and data recording. A twofold change in SEM magnification size gave rise to a 7% deviation, and scaling up from the original image increased the discrepancy compared to miniaturization. In conclusion, texture characterization is useful for estimating the fractal properties of most chain-like or cluster soot aggregates.