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Soot Scattering Measurements in the Visible and Near-Infrared Spectrum
ILLINOIS UNIV AT CHICAGO DEPT OF MECHANICAL ENGINEERING
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Scattering to extinction cross section ratios, qse, were measured using the NIST Large Agglomerate Optics Facility for soot produced from ethene and acetylene laminar diffusion flames. Measurements were performed using light sources at 543.5 nm, 632.8 nm, and 856 nm. The average scattering to extinction cross section ratios for these wavelengths are equal to 0.245, 0.195, and 0.195 for ethene and 0.311, 0.228, and 0.237 for acetylene. The 856 nm measurements represent the longest wavelength for which accurate scattering measurements have been performed for soot. The size distribution and fractal properties of the two soots were determined to assess the effects of limited acceptance angle range, finite size of the sensor, and departure from cosine response on the uncertainty in the measurement of qse. The expanded relative uncertainty 95 confidence level was found to be - 6 at the two visible wavelengths and - 8 at 856 nm. Both the magnitude and wavelength dependence of rho sub se for the present experiments are significantly different from those reported by Krishnan et al. for overfire soot produced using a turbulent flame. The results are compared with the predictions of fractal optics.
APPROVED FOR PUBLIC RELEASE