Spectrally Resolved Measurement of Flame Radiation to Determine Soot Temperature and Concentration

Amultiwavelength  ame emission technique is developed for high spatial resolution determination of soot temperature and soot volume fraction in axisymmetric laminar diffusion  ames. Horizontal scans of line-integrated spectra are collected over a spectral range of 500–945 nm. Inversion of these data through one-dimensional tomography using a three-point Abel inversion yields radial distributions of the soot radiation from which temperature proŽ les are extracted. From an absolute calibration of the  ame emission and by use of these temperature data, absorption coefŽ cients are calculated, which are directly proportional to the soot volume fractions. The important optical parameters are discussed. It is shown that a uniform sampling cross section through the  ame must be maintainedand that variations in samplingarea produce inconsistencies between measurements and theory,which cannotbe interpreted as spatial averagingof the property Ž eld. The variations in cross-sectional samplingarea have the largest in uence on the measurements at the edges of the  ame, where the highest resolution is required. Emission attenuation by soot has been shown to haveminor in uence on the soot temperature and soot volume fraction for the soot loading of the axisymmetric  ame tested. An emission correction scheme is outlined, which could be used for more heavily sooting  ames. For a refractive index absorption functionE(m) = Im[(m2 ¡¡ 1)/(m2 + 2)] that is independent of wavelength, the soot temperatures and soot volume fractions measured with this technique are in excellent agreement with data obtained by coherent anti-Stokes Raman scattering nitrogen thermometry and two-dimensional soot extinction in the same ethylene co ow diffusion  ame. The agreement of the results suggests a limit of the slope of the spectral response of E(m) to be between 0 and 20% over the spectral range examined.