Sizing of droplets in reactive fuel sprays by Mie scattering imaging

In this paper the application of the Mie Scattering Imaging technique to droplets in reactive sprays, namely to non-homogeneous droplets, is discussed for the first time. A theoretical analysis of light scattering by radially inhomogeneous spheres with different complex refractive index profiles was carried out. Both transparent and absorbing inhomogeneous droplets were examined. The light scattering by radially inhomogeneous droplets was computed by the Finely Stratified Sphere Scattering Model. The theoretical analysis based on both the Lorenz-Mie theory and on FSSSM showed that in forward at a scattering angle ?=60° the angular oscillation spacing is almost constant and depends on the droplet size with the relation: ??(?, m(r), D) ? 1.12×180°/(pi*D/?). At this angle the oscillations are regular and the influence of the refractive index is small. Thus, even if the droplet refractive index is completely unknown it is possible to measure the size of a droplet by measuring the angular oscillation spacing. The weak dependence of ?? on the refractive index results in an uncertainty on the measure of the droplet size of about 4%.