Experimental determination of scattering matrix of fire smoke particles at 532 nm

Abstract

Based on polarization modulation and lock-in detection, an experimental apparatus is built to determine several important angular dependent scattering matrix elements at 532 nm. The apparatus is tested by water droplets through comparing measurement results with Mie calculations. Measurement results of scattering matrix elements and element ratios between smoke particles produced by smoldering cotton test fire and those produced from flaming n-heptane test fire are presented. We find that results of Mie calculations are able to describe the experimental data of smoldering cotton test fire smoke, which indicates that the particles generated by smoldering cotton test fire are mostly spherical in shape with considering the particle size relative to the wavelength. Using the optimization method, we estimate the refractive index (m=1.49+i0.01) and size distribution (lognormal distribution, g=2.335 and dg=0.17 m) of smoldering cotton test fire smoke. Contrarily, the experimental data of flaming n-heptane fire smoke cannot be described by Mie scattering, which is interpreted by the nonspherical, fractal aggregate morphology of the particulates.