PREDICTION OF SCATTERING EFFECT BY ASH POLYDISPERSION ON SPECTRAL EMISSION FROM COAL-FIRED MHD COMBUSTION GAS

Scattering effects by ash polydispersion on spectral emission from the coal-fired MHD combustion gas are predicted numerically by means of t he first (P-1) and third (P-3) spherical harmonics approximations of a radiative transfer equation in a rectangular cross section of the MHD power generation 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 ind ex. Results of P-1 approximation agree well with those of P-3 approxim ation when an optical thickness is greater than about 2. Scattering ef fects can be neglected for a large optical thickness and a small scatt ering albedo, but precise calculation is needed to get the radiation i ntensity distribution when the absorption coefficient of combustion ga s is of the same order of magnitude as the scattering of absorption co efficient of the ash polydispersion. The self-resonant absorption of p otassium 4P-4S spectrum measured through an observation port in the pr esence of a cold boundary layer is not predicted by the P-1 approximat ion with an emitting and absorbing slag wall.