Uo. Koylu et Gm. Faeth, SPECTRAL EXTINCTION COEFFICIENTS OF SOOT AGGREGATES FROM TURBULENT-DIFFUSION FLAMES, Journal of heat transfer, 118(2), 1996, pp. 415-421
The spectral extinction coefficients of soot aggregates were studied i
n the fuel-lean (overfire) region of buoyant turbulent diffusion flame
s. Extinction measurements were carried out in the wavelength region o
f 0.2-5.2 mu m for flames fueled with acetylene, propylene, ethylene,
and propane, burning in air. The present measurements were combined wi
th earlier measurements of soot morphology and light scattering at 0.5
14 mu m in order to evaluate the spectral soot refractive indices repo
rted by Dalzell and Sarofim (1969), Lee and Tien (1981), and Chang and
Charalampopoulos (1990). The specific extinction coefficients and emi
ssivities were predicted based on Rayleigh-Debye-Gans theory for polyd
isperse fractal aggregates, which has been recently found to be the be
st approximation to treat optical cross sections of soot aggregates. T
he results indicated that available refractive indices of soot do not
predict the spectral trends of present measurements in the ultraviolet
and infrared regions. Soot complex refractive index was inferred to b
e m = 1.54 + 0.48i at 0.514 mu m, which is surprisingly in best agreem
ent with the values reported by Dalzell and Sarofim (1969). Additional
ly, specific extinction coefficients of soot aggregates varied with wa
velength as lambda(-0.83) from the visible to the infrared. Finally so
ot refractive indices were found to be relatively independent of fuel
type for the visible and infrared spectral regions over the H/C ratio
range of 0.08-0.22.