| This study describes the measurements of the dimensionless extinction constant, Ke, of soot in the visible and infrared spectrum using the NIST Large Agglomerate Optics Facility (LAOF). Soot was produced using a 11 mm i.d. laminar diffusion flames burner fueled with acetylene and ethene. Light extinction measurements were performed using light sources at 543.5 nm, 632.8 nm, 856 nm, 1314 nm, and 1565 nm. The mean values of present measurements of Ke range from 7.95 to 10.0. These unique experiments provide accurate values of Ke to be used for measurements of soot concentration and temperature in the infrared spectrum. These measurements represent the first fuel-specific data available in the near-infrared spectrum. Transmission electron microscopy and optical microscopy analyses were used to analyze soot morphology and aerosol properties to estimate the influences of beam shielding and light scattering on the observed variations of K e.; Scattering to extinction cross-section ratios, ρse, were also 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 ρse. The expanded relative uncertainty (95% confidence level) was found to be ±6% at the two visible wavelengths and ±8% at 856 nm. The results are compared with the predictions of fractal optics. |
