Soot Pyrometry by Emission Measurements at Different Wavelengths in Laminar Axisymmetric Flames

In this work, a multi-wavelength pyrometry method is proposed in order to evaluate soot temperature for laminar axisymmetric non-premixed flames. A single radiative model that combines three detection wavelengths is developed to increase the spectral information used in the soot temperature determination. A simple set-up is used in order to capture the soot emission at two or three wavelengths. The robustness of the methodology is assessed by a radiative model, which includes a sensitivity and relative error analysis for the soot temperature, and accounts for self-absorption effects. The model and procedure are verified by employing numerical temperature and soot volume fraction fields to recreate the convoluted soot emissions. Soot emission measurements involve different combinations of wavelengths that are employed to evaluate soot temperature without requiring additional measurements of the soot absorption coefficient when soot self-absorption is neglected. The error on the determined soot temperature was estimated to be lower than 60 K under this assumption for soot volume fractions under 10 ppm. In addition, an analysis of the signal noise effect on the temperature shows that the modulated absorption/emission (MAE) technique is more sensitive than the emission (EMI) technique. A sensitivity analysis showed that the presented three-wavelength EMI model is less sensitive to small deviations on the measured soot emission ratio than the classical two-wavelength approach. This feature makes the model suitable to improve the accuracy on the determination of soot temperature when the noise level of the signal is significant.