Simultaneous Optical Measurement of Soot Volume Fraction and Temperature in Premixed Flames.
Simultaneous Optical Measurement of Soot Volume Fraction
and Temperature in Premixed Flames.
(819 K)
Choi, M. Y.; Hamins, A.; Mulholland, G. W.; Kashiwagi,
T.
Combustion and Flame, Vol. 99, 174-186, 1994.
Keywords:
soot; temperature; premixed flames; absorption;
emission; extinction; scattering; temperature
measurements
Abstract:
The performance of a three-wavelength optical probe
technique for measuring soot volume fraction and
temperature was assessed by conducting experiments in
the homogeneous environment of a premixed flame. Using
a premixed ethylene/air flame, the temperatures and soot
volume fractions (fva, based on absorption measurements
at 633 nm and fve, based on emission measurements at 900
nm and 1000 nm) were compared with previously reported
results. Although the temperatures and mean soot volume
fractions compared favorably, the discrepancy between
fva and fve prompted new measurements to evaluate the
importance of source wavelength on the fva measurements,
scattering by soot particles, light absorption by
"large" molecules and the use of different indices of
refraction reported in the literature. The experiments
on the degree of soot scattering and light absorption by
"large" molecules indicated that these effects cannot
reconcile the observed discrepancy in the soot volume
fractions. The measured soot volume fractions were,
however, sensitive to the absorption constant and
therefore varied significantly when different sets of
refractive indices were used. Furthermore, the
agreement between fva and fve was improved when
extinction measurements were performed with longer
wavelength light sources. Isokinetic soot sampling
experiments were also performed to compare with the
optically-measured soot volume fractions. This
technique does not rely on the refractive indices of
soot and therefore provides an independent measure of
the soot volume fraction. The soot volume fractions
measured using this technique compared favorably with
the optically measured values (calculated using various
indices of refraction).
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899