Prediction of Light Scattering Effect by Ash Polydispersion on Spectral Emission from Coal-Fired MHD Combustion Gas

Abstract

Light scattering effects by ash polydispersion on spectral emission from coal-fired MHD combustion gas are predicted numerically by means of the first (P₁) and third (P₃) spherical harmonics approximations of a radiative transfer equation in a rectangular cross section of the MHD channel, with consideration of variation in optical properties across a boundary layer, particle diameter distribution of ash polydispersion and wavelength change of ash complex refractive index. Results of P₁ approximation agree well with those of P₃ approximation when optical thickness is greater than about 2. Scattering effects can be neglected for a large optical thickness and a small scattering albedo, but precise calculation is needed when the absorption coefficient of the combustion gas is of the same order of magnitude as the scattering or absorption coefficient of the ash polydispersion.