Transient Structure and Radiation Properties of Strongly Radiating Buoyant Flames

Measurements of instantaneous temperature and soot volume fractions based on absorption and emission in highly buoyant turbulent acetylene/air and propylene/air flames are reported. These measurements are used to predict mean, rms, probability density functions, and power spectral densities of spectral radiation intensities along a representative horizontal chord in the flame. The results show the presence of large quantities of relatively cold soot in the vicinity of smaller amounts of hot soot particles. The resulting inhomogeneity in the temperature of soot in the flame leads to negative cross correlations between temperature and soot volume fractions. The treatment of such correlations was found necessary for predicting the observed probability density functions and the power spectral densities of spectral radiation intensities.