On The Refractive Index of Soot at Flame Temperature

Data of the optical constants of soot at flame temperature are presented for the visible and infrared regions (0.4-5 μm). Both real and imaginary parts of the refractive index are determined from in-situ extinction coefficient spectra by fitting to theoretical spectra calculated by using the Mie theory in conjunction with a dispersion model. Particle size used in Mie calculation is experimentally determined by using the Diffusion Broadening Spectroscopy technique. Results are presented for different premixed flat flames (methane, propane and ethylene). It is shown that for high H/C ratio in soot, ie.,≥ 0.2, the imaginary part of the refractive index is much less than what is generally considered. Consequently, soot volume fraction determined by light scattering techniques is underestimated in some situations.