Quantitative Two-Photon Laser-Induced Fluorescence Imaging of CO in Flickering CH4/Air Diffusion Flames.
Quantitative Two-Photon Laser-Induced Fluorescence
Imaging of CO in Flickering CH4/Air Diffusion Flames.
Everest, D. A.; Shaddix, C. R.; Smyth, K. C.
Combustion Institute, Symposium (International) on
Combustion, 26th. Proceedings. Volume 1. July
28-August 2, 1996, Napoli, Italy, Combustion Institute,
Pittsburgh, PA, 1161-1169 pp, 1996.
combustion; carbon monoxide; diffusion flames;
flickering flames; laser-induced fluorescence; methane;
polycyclic aromatic hydrocarbons; soot
One-dimensional fluorescence imaging measurements of CO
concentrations have been made in steady and flickering
axisymmetric, methane/air diffusion flames burning at
atmospherric pressure. These experiments extend
fluorescence detonation of CO to flames that contain
significant soot volume fractions, approximately 1-2 x
10-6. Our aim is to quantify changes in the CO levels
that occur for flickering conditions, where increased
soot production and subsequent oxidation may have
important effects. The Q branch (0,0) band of the
[equation] transition was excited near 230 nm in a
two-photon process, and the [equation] band fluorescence
was detected at 483.5 nm. Quenching-independent data
were obtained, and interferences from boradband
molecular fluorescence and soot incandescence were
accounted for by subtracting profiles measured for
excitation at a nearby, nonresonant wavelength. Maximum
CO concentrations are found to be approximately equal in
the steady and flicering flames burning with the same
fuel flow rate. For the flickering flames, the greater
radial extent of the burning flamelet following clip-off
yields approximately 50-65% larger volume-integrated CO
levels. Overall, this increase in CO production is
modest compared to the factor of 4 enhancement observed
in the time-averaged, volume-integrated, soot volume
fraction, indicating that soot oxidation does not appear
to appreciably impact CO levels in these methane flames.