Measurement of submicrometer Al_2O_3 particles in plumes

Abstract

We made multiple-wavelength light transmission measurements at the edge of a plume from a small solid-propellant motor in order to determine the mean particle size and the in situ particle index of refraction. We retrieved the particle size distribution from the Sauter mean diameter and the geometrical standard deviation assuming a lognormal distribution. The good correlation of the data indicated the applicability of the technique with a relatively high confidence level and that submicrometer particles were dominantly present at the edge of the plume. This was confirmed by the size distribution of collected particles. The values measured for alumina particles in the edge of the plume were a Sauter mean diameter of 0.150 µm ± 4%, a geometrical standard deviation of 1.50 ± 3%, and a real index of refraction of 1.63 ± 8%.