In-situ measurements of alumina particle size and optical constants in composite solid propellant flames

The complex refractive index (n-ik) at 0.6328ym and the effective optical diameter of alumina particles in ammonium perchlorate (AP) composite solid propellant flames were measured in-situ using an inverse light scattering technique. Measured bidirectional reflectance and transmittance values were used to obtain n values, between 1.3 and 1.8 and k values between 0.04 and 0.6. The effective alumina diameter was determined (by the absence or existence of solutions to the Inverse scattering problem) to be between 0.26 and 0.30 um. Forward scattering dominated back scattering to such an extent that even a linear anisotropic scattering model would be inaccurate in describing the radiative transport. The alumina single scattering albedo was found to be in the range 0.5 to 0.7.