Optical properties in the visible of overfire soot in large buoyant turbulent diffusion flames

Nonintrusive measurements of the optical properties of soot at visible wave lengths (351.2-800.0 nm) were completed for soot in the overfire region of large (2-7 kW) buoyant turbulent diffusion flames burning in still air at s tandard temperature and pressure, where soot properties are independent of position and characteristic flame residence time for a particular fuel. Soo t from flames fueled with gaseous (acetylene, ethylene, propylene, and buta diene) and liquid (benzene, cyclohexane, toluene, and n-heptane) hydrocarbo n fuels were studied. Scattering and extinction measurements were interpret ed to find soot optical properties using the Rayleigh-Debye-Gans/polydisper se-fractal-aggregate theory after establishing that this theory provided go od predictions of scattering patterns over the present test range. Effects of fuel type on soot optical properties were comparable to experimental unc ertainties. Dimensionless extinction coefficients were relatively independe nt of wavelength for wavelengths of 400-800 nm and yielded a mean value of 8.4 in good agreement with earlier measurements. Present measurements of th e refractive index function for absorption, E(m), were in good agreement wi th earlier independent measurements of Dalzell and Sarofim and Stagg and Ch aralampopoulos present values of the refractive index function for scatteri ng, F(m), however, only agreed with these earlier measurements for waveleng ths of 400-500 nm but otherwise increased with increasing wavelength more r apidly than the rest. The comparison between present and earlier measuremen ts of the real and imaginary parts of the complex refractive index was simi lar to E(m) and F(m).