Effect of soot self-absorption on color-ratio pyrometry in laminar coflow diffusion flames.

This Letter reports on the effect of self-absorption on measured temperature for color-ratio soot pyrometry with a color camera. A series of increasingly nitrogen diluted atmospheric pressure ethylene/air laminar coflow diffusion flames are studied, providing flames with different optical path lengths, soot loading, and soot optical properties. Numerical calculations are used to simulate the change in collected flame emission signal with and without light attenuation using experimentally measured maps of the soot absorption coefficient. This parameter implicitly contains information about soot volume fraction and soot optical properties. The ratio of these calculations is used to correct the raw color-channel signals, resulting in temperature maps with improved accuracy. The change in calculated temperature varies spatially within each flame, with the maximum correction quantified to be 22 K for a flame with a maximum optical depth of 0.31. This correction is as much as 42 and 75 K for simulated flames with the same optical properties, structure, and a factor of two and five increase in soot volume fraction, respectively.