Extinction and scattering properties of soot emitted from buoyant turbulent diffusion flames

Extinction and scattering properties at wavelengths of 250-5200 nm were stu died for soot emitted from buoyant turbulent diffusion flames in the long r esidence time regime where soot properties are independent of position in t he overfire region and characteristic flame residence times. Flames burning in still air and fueled with gas (acetylene, ethylene, propane, and propyl ene) and liquid (benzene, toluene, cyclohexane, and n-heptane) hydrocarbon fuels were considered. Measured scattering patterns and ratios of total sca ttering/absorption cross sections were in good agreement with predictions b ased on the Rayleigh-Debye-Gans (RDG) scattering approximation in the visib le. Measured depolarization ratios were roughly correlated by primary parti cle size parameter, suggesting potential for completing RDC methodology nee ded to make soot scattering predictions as well as providing a nonintrusive way to measure primary soot particle diameters. Measurements of dimensionl ess extinction coefficients were in good agreement with earlier measurement s for similar soot populations and were independent of fuel type and wavele ngth except for reduced values as the near ultraviolet was approached The r atios of the scattering/absorption refractive index functions were independ ent of fuel type within experimental uncertainties and were in good agreeme nt with earlier measurements. The refractive index function for absorption was similarly independent of fuel type but was larger than earlier reflecto metry measurements in the infrared Ratios of total scattering/absorption cr oss sections were relatively large in the visible and near infrared, with m aximum values as large as 0.9 and with values as large as 0.2 at 2000 nm, s uggesting greater potential for scattering from soot particles to affect fl ame radiation properties than previously thought.