Detailed Spectral Radiation Calculations for Nonhomogeneous Soot/Gas Mixtures Based on a Simulated Ethylene Jet Diffusion Flame

摘要

The purpose of this paper is to study the effects of the radiative properties of soot particles and CO2 and H2O gases on detailed radiative heat transfer calculations using a simulated ethylene jet diffusion flame. The YIX method is applied to calculate the radiative transfer quantities over the spectral range of 1-20 micrometers in a finite cylindrical enclosure with distributions for flame temperature, soot volume fraction, and gas concentrations precalculated from a modeling analysis. Scattering from soot particles is neglected. Soot only, gases only, and the combined cases are examined. The Rayleigh solution is used to calculate the absorption coefficient spectra for soot aggregates. Soot complex refractive index spectra are generated from the Drude-Lorentz dispersion model based on three frequently cited dispersion parameter sets. Results from these three dispersion parameter sets show that the difference in maximum flux divergence is 45 and that the difference in maximum radial flux is 62. Thus current uncertainties about soot spectral refractive indices are the main limitation on accurate estimates of the radiation heat transfer from sooting combustion systems. The exponential-wide-band model is used to calculate gas absorption coefficient spectra. Generally, radiation from soot is two to three times of that from gases. Therefore both soot and gas contributions are significant, and accurate models for gas absorption coefficient spectra are crucial. More than 95 of the total gas radiation comes from the 2.73 and 4.3 micrometer bands of CO2 and from the 2.67 micrometer bands of H2O. The 6.3 micrometer H2O band can be added to essentially account for all gas radiation, and other gas absorption bands make very little contribution. Practically, for the type of flames considered here, it is concluded that spectral contributions from beyond the 5 micrometer range can be neglected with less than 5 loss of accuracy in calculating the total radiative flux and its divergence.