Morphology of soot collected in microgravity droplet flames

Measurements of the primary particle size, radius of gyration, fractal dimension, and the mass fractal prefactor were measured for soot sampled in n-heptane droplet flames under microgravity conditions. These represent the first such measurements obtained for spherically symmetric droplet flames. Experiments were performed in the NASA-Glenn Research Center in Cleveland, OH. Soot was sampled at 0.2 and 0.5 s after ignition for a 2.1 mm droplet burning in atmospheric pressure air. The measured primary particle sizes were significantly larger under microgravity conditions compared to normal gravity and were found to increase with residence time. The average radius of gyrations were also larger for soot collected in microgravity conditions. Differences in the particle and agglomerate dimensions are believed to be caused by the longer residence times. The fractal dimensions were found to be nearly constant for all experiments while the prefactor term was found to increase slightly with residence time.