2367 Proceedings of the Combustion Institute, Volume 29, 2002/pp. 2367–2374 MEASUREMENT OF VISIBLE AND NEAR-IR OPTICAL PROPERTIES OF SOOT PRODUCED FROM LAMINAR FLAMES JINYU ZHU, 1 MUN YOUNG CHOI, 2 GEORGE W. MULHOLLAND, 3 SAMUEL L. MANZELLO, 3 LOUIS A. GRITZO 4 and JILL SUO-ANTTILA 4 1 Department of Mechanical Engineering University of Illinois at Chicago Chicago, IL 60607, USA 2 Department of Mechanical Engineering and Mechanics Drexel University Philadelphia, PA 19014, USA 3 Building and Fire Research Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899, USA 4 Fire Science and Technology Sandia National Laboratory Albuquerque, NM 87185, USA 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 exper- iments provide accurate values of K e 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 mea- sured K e 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 . Introduction Particulate emission from mobile and stationary sources burning hydrocarbon fuels creates environ- mental and health hazards. It was recently estimated that 60,000 people die prematurely each year from soot inhalation [1]. Soot production is also one of the major causes of process inefficiency in energy con- version systems and causes deleterious fouling of hardware. Soot particles affect the environment in many ways, including contributions to the formation of photochemical smog [2,3] and atmospheric acids [4]. Soot particles released into the atmosphere scat- ter and absorb solar radiation that can degrade at- mospheric visibility. Accurate measurement of soot emitted from these sources is therefore important for gauging the posed environmental hazards, health impacts, and fire safety issues. Soot particle concentrations are typically mea- sured using a non-intrusive light extinction tech- nique. In this technique, the ratio of the transmitted to the incident light intensity is used to obtain the soot volume fraction, f v , I f v  exp  K L (1) e   I k 0 where K e is the dimensionless soot extinction con- stant, L is the path length through the soot, and k is the wavelength of the light source. K e computed in the Rayleigh-Debye limit is composed of the dimen- sionless absorption constant, K a , and the dimension- less scattering constant, K s [5], 3 2 4px nF(m) p K  6pE(m); K  a s 1 n D /2 2 f 16p 2 1  R (2a–b) g   2 3D k f where n 1 and n 2 are the first and second moments of the agglomerate size probability distribution func- tion, R g is the radius of gyration of the soot agglom- erates, x p is the optical size parameter (x p  pd p /k), D f is the fractal dimension, m is the complex index of refraction for soot, d p is the soot primary particle