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.