Radiation properties of soot from diffusion flames

The spectral extinction coefficients kλof soot from flame transmission data are obtained for small pool diffusion flames of various fuels including solid polystyrene and plexiglas; foam polystyrene and polyurethane; and liquid isooctane and toluene. Good agreement between experimental and predicted kλfrom Mie theory and soot optical properties throughout the visible and infrared ranges substantiates the general applicibility of these optical properties. On the other hand, the determination of soot sizes and volume fractions from visible range data and optical properties requires the form of the size distribution be known. The effect of using different size distributions on these soot results is evaluated by using the three-parameter distribution for the particle number density N(r) = arbexp (-br/rm), with b varied to create different functional dependence on radius r. The most probable radius rmis found to increase by about 80% as b is changed from 2 to 6, while the volume fraction changes by less than 10%. Hence, the most probable radius is rather sensitive to this functional dependence, while the volume fraction is only slightly affected.