Soot pyrometry using modulated absorption/emission

A new method of optical pyrometry for sooting flames has been developed that combines absorption and emission measurements at the same wavelength, reducing the uncertainty in measured soot temperature when compared to commonly used two-color emission pyrometry. The new technique, modulated absorption/emission (MAE) pyrometry, utilizes combined emission and absorption at two wavelengths: 830 and 1300 nm. Large uncertainties in the wavelength-dependent soot refractive index in the infrared are avoided by measuring emissivity directly, eliminating the need to rely on a refractive index model when obtaining temperature. One-color and two-color MAE techniques are validated in this study in a rich laminar premixed ethylene/air flame using diode lasers for transmission measurements. The results show a reduction in the uncertainty of measured temperature in an example case from greater than +/- 50 K with conventional emission-only pryometry to +/- 20 K with MAE pyrometry. Advantages of MAE over the. conventional method are greatest for soot volume fractions on the order of 10(-7) or greater, typical of laboratory flames used in soot formation and growth studies. (C) 2001 by The Combustion Institute.