Cs. Mcenally et al., SOOT VOLUME FRACTION AND TEMPERATURE-MEASUREMENTS IN LAMINAR NONPREMIXED FLAMES USING THERMOCOUPLES, Combustion and flame, 109(4), 1997, pp. 701-720
Thermocouple particle densitometry (TPD), a new method for measuring a
bsolute soot volume fraction in flames which was suggested by Eisner a
nd Rosner, has been successfully implemented in several laminar nonpre
mixed flames. This diagnostic relies on measuring the junction tempera
ture history of a thermocouple rapidly inserted into a soot-containing
flame region, then optimizing the fit between this history and one ca
lculated from the principles of thermophoretic mass transfer. The TPD
method is very simple to implement experimentally, yields spatially re
solved volume fractions directly, can easily measure small volume frac
tions, and does not depend on the prevailing soot particle size, morph
ology, or optical characteristics. In a series of methane and ethylene
counterflow flames whose soot volume fractions varied by more than an
order of magnitude, the TPD results agreed to within experimental err
or with our own laser extinction measurements. In axisymmetric methane
and ethylene co-flowing flames, the shape of TPD profiles agreed well
with published laser extinction measurements, but the TPD concentrati
ons were significantly larger in the early regions of the ethylene fla
me and throughout the methane flame; these discrepancies are probably
attributable to visible light-transparent particles that are detectabl
e with TPD but not with laser extinction. The TPD method is not applic
able to the upper regions of these co-flowing flames since OH concentr
ations there suffice to rapidly oxidize any soot particles that deposi
t. Gas temperatures were obtained simultaneously with volume fraction
by averaging the junction temperature history shortly after insertion.
The error in these temperatures due to soot deposition-imposed change
s in the junction diameter and emissivity were assessed and found to b
e moderate, e.g., less than 60 K near the centerline of the ethylene c
oflowing flame where the volume fraction was 6 ppm and the gas tempera
ture was 1550 K. (C) 1997 by The Combustion Institute.