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A two-color version of the laser-induced incandescence (2C-LII) technique was implemented for measuring absolute soot volume fraction in flames. By using a calibrated tungsten ribbon lamp, soot peak temperatures were measured as a function of fluence at several locations in an ethylene diffusion flame by using a steeply edged laser beam profile. Above a certain fluence threshold, peak temperatures were tightly distributed just above 4000 K independent of the particle size and number density. Radial profiles of soot volume fraction were obtained and compared (not calibrated) with results from the laser extinction technique. Good agreement showed the validity of the 2C-LII technique at a controlled fluence.

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A two-dimensional soot diagnostic technique has been developed as an extension of the well-known two-color pyrometry. Two flame images are simultaneously collected on a CCD at selected wavelengths through suitable optics. By use of the dependence of soot emissivity on the soot volume fraction and by comparison with images from a calibrated light source, both the temperature field and the soot distribution can be determined. Validation was carried out through data obtained with other soot diagnostic methods on ethylene diffusion and Diesel oil-rich premixed flames. The current technique readily allowed us to obtain a large amount of data for a thorough description of the soot distribution within the flame. As an example of the technique's potential, data about methane and propane diffusion flames are reported.