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Elusive History of m=1.57-0.56i for the Refractive Index of Soot. Brief Communication.


pdf icon Elusive History of m=1.57-0.56i for the Refractive Index of Soot. Brief Communication. (436 K)
Smyth, K. C.; Shaddix, C. R.

Combustion and Flame, Vol. 107, No. 3, 314-320, November 1996.

Keywords:

soot; refractive index; time measurement

Abstract:

Soot volume fractions, number densities, and particle sizes have been extensively measured in laboratory flames using combined extinction and scattering methods. In order to obtain quantitative results, a value of the complex refractive index of the soot must be chosen, appropriate for the wavelength employed in the experimental measurements. Recent quantitative soot volume fraction determinations using laser-induced incandesence also rely on a proper calibration, which is usually based on extinction-derived soot concentrations. Soot refractive indices have been reported for over 30 years, during which time measurement techniques have evolved considerably. Extractive, room-temperature compressed pellet reflectance methods have been replaced, for example, by in situ determinations using combined classical and dynamic light scattering. Despite many measurements of the refractive index of soot, m=1.57 - 0.56i is still by far the result most often cited in the combustion community for visible wavelengths. This value has been widely attributed to Dalzell and Sarofim, although it is not included in their experimental data in either the visible or near-IR wavelength regions.