Soot pyrometry using modulated absorption/emission

A new method of optical pyrometry for sooting flames has been developed tha t combines absorption and emission measurements at the same wavelength, red ucing the uncertainty in measured soot temperature when compared to commonl y used two-color emission pyrometry. The new technique, modulated absorptio n/emission (MAE) pyrometry, utilizes combined emission and absorption at tw o wavelengths: 830 and 1300 nm. Large uncertainties in the wavelength-depen dent soot refractive index in the infrared are avoided by measuring emissiv ity directly, eliminating the need to rely on a refractive index model when obtaining temperature. One-color and two-color MAE techniques are validate d in this study in a rich laminar premixed ethylene/air flame using diode l asers for transmission measurements. The results show a reduction in the un certainty of measured temperature in an example case from greater than +/- 50 K with conventional emission-only pryometry to +/- 20 K with MAE pyromet ry. Advantages of MAE over the. conventional method are greatest for soot v olume fractions on the order of 10(-7) or greater, typical of laboratory fl ames used in soot formation and growth studies. (C) 2001 by The Combustion Institute.