Measurement of visible and near-IR optical properties of soot produced from laminar flames

This study describes the measurements of the dimensionless extinction constant, K-e, of soot in the visible and IR spectrum using the National Institute of Standards and Technology Large Agglomerate Optics Facility. Soot was produced using a 11 mm i.d. laminar diffusion flame burner fueled with acetylene and ethene. Light extinction measurements were performed using light sources at 543.5, 632.8, 856, 1314, and 1565 nm. The mean values of present measurements of K-e range from 7.95 to 10.0. These unique experiments provide accurate values of K, to be used for measurements of soot concentration and temperature in the IR spectrum. These measurements represent the first fuel-specific data available in the near-IR spectrum. The measured K, values for all wavelengths are significantly larger than values calculated using reported values of the refractive index and the Rayleigh theory. 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.