Minor-species structure of premixed cellular tubular flames
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2014, American Institute of Aeronautics and Astronautics Inc. All rights reserved. Quantitative measurements of hydrogen atoms and hydroxyl radicals are reported of cellular phenomena in lean laminar premixed hydrogen-fueled tubular flames. Femtosecond two-photon laser-induced fluorescence (fs-TPLIF) enables photolytic-interference-free measurement of H-atoms. Quenching corrections are calculated from temperature and major species measurements determined by spontaneous Raman scattering. Two diluents are used (N2, CO2) to provide sub-unity Lewis numbers and highly curved cellular flame structure. The strong effect of thermal-diffusive imbalance is observed through clear local extinction (lack of H-atoms). Peak number densities on the order of 1015 cm-3 for H-atoms and 1016 cm-3 for OH radicals are measured within the reaction cells. A conflicting sensitivity of flame structure on stretch rate is found between the cases considered, and compared to non-cellular tubular flame numerical predictions. The mechanism for cellular instability is found to be supported by thermal-diffusive imbalance, but the underlying mechanism for the transition from a non-cellular to cellular form is unclear.
