Nonluminous Radiation in Turbulent Buoyant Axisymmetric Flames

Abstract

A theoretical and experimental study of nonluminous radiation properties of turbulent, buoyant, axisymmetric, methane diffusion flames burning in still air is reported. Spectral radiance was measured along radial paths within and near the luminous portion of three flames whose structure was studied earlier in this laboratory. Predictions of spectral radiance were found by solving the equation of radiative transfer along the same paths. A narrow-band model was used with flow structure predicted by the conserved scalar formalism of a k-ε-g turbulence model. The computations were based on mean properties as well as a stochastic method which allowed for turbulent fluctuations. In general, the stochastic method overestimated the measured spectral radiances by 10-30 percent, while the mean property method was in reasonably good agreement with measurements. Therefore, while turbulent fluctuations have a significant influence on non-luminous radiation properties of the present flames, the effect is comparable to uncertainties in current flame structure and narrow-band models.