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Quantitative Two-Photon Laser-Induced Fluorescence Imaging of CO in Flickering CH4/Air Diffusion Flames.


pdf icon Quantitative Two-Photon Laser-Induced Fluorescence Imaging of CO in Flickering CH4/Air Diffusion Flames. (832 K)
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.

Keywords:

combustion; carbon monoxide; diffusion flames; flickering flames; laser-induced fluorescence; methane; polycyclic aromatic hydrocarbons; soot

Abstract:

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.