Fractal Properties of Smoke Produced From Smoldering and Flaming Fires

This report presents the initial results of experiments to determine the fractal-like properties of aggregate smoke particles produced from both smoldering and flaming fires. In the experiments, angular intensity data were acquired in order to determine the fractal dimension, D_f, radius of gyration, R_g, and albedo, ω, for smoke produced from smoldering coal and wood, flaming coal and wood, a pool fire of No. 2 diesel fuel, and the smoke produced at the exhaust of a diesel engine. This data was combined with simultaneous measurements of current reduction in a calibrated ionization chamber detector and independent measurements of specific extinction for the different types of smoke in order to determine the primary particle diameters for the aggregate smoke particles. Both types of smoldering fires yielded similar fractal properties, and the three types of flaming fires also possessed similar fractal properties, but significant differences exist between the smoldering and flaming properties. The characteristics of smoke from the diesel engine were similar to those of smoke from the flaming fires, yet distinct Smoldering aggregates appear to be composed of a small number (≃ 100) of large primary particles (d_p ≃ 0.07 μm), while flaming aggregates are composed of a large number (≃ 1000) of small primary particles (d_p ≃ 0.025–0.035 μm). The average ω’s of smoldering aggregates are a factor of 2 to 3 larger than those of the flaming aggregates. In addition, further analysis indicates that the complex component of the index of refraction, i.e., the extinction coefficient, k, is a factor of 2 to 3 lower for the smoldering aggregates compared to the flaming aggregates. The implications of these results are also discussed.