Photofragmentation laser-induced fluorescence imaging in premixed flames

Research output: Contribution to journalArticle

Abstract

Two-dimensional measurements of primarily hydroperoxyl radicals (HO2) are, for the first time, demonstrated in flames. The measurements are performed in different Bunsen-type premixed flames (H-2/O-2. CH4/O-2, and CH4/air) using photofragmentation laser-induced fluorescence (PF-LIF). Photofragmentation is done by laser radiation at 266 nm, and the generated OH photofragments are probed through fluorescence induced by a laser tuned to the Q(1)(5) transition at 282.75 nm. The signal due to naturally occurring OH radicals, recorded by having the photolysis laser blocked, is subtracted, providing an image that reflects the concentration of OH fragments generated by photolysis, and hence the presence of primarily HO2, but also smaller contributions from H2O2 and, for the methane flames, CH3O2. For the methane flames the measured radial profiles of OH photofragments and natural OH agree well with corresponding profiles calculated for laminar, one-dimensional, premixed flames using CHEMKIN-II with the Konnov detailed C/H/N/O reaction mechanism. An interfering signal contribution is observed in the product zone of the methane flames. It is concluded that the major source for the interference is most likely hot CO2, from which 0 atoms are produced by photolysis, and OH is rapidly formed as the O atoms react with H2O and H-2. This conclusion is supported by the fact that the interference is absent for the hydrogen flame, but appears when CO2 is seeded into the flame. Another strong indication is that the Konnov mechanism predicts a similar buildup of OH after photolysis. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Atom and Molecular Physics and Optics

Keywords

  • Combustion diagnostics, Photofragmentation, Laser-induced fluorescence, Hydrogen peroxide, Hydroperoxyl radical, Methyl peroxy radical
Original languageEnglish
Pages (from-to)1908-1919
JournalCombustion and Flame
Volume158
Issue number10
Publication statusPublished - 2011
Publication categoryResearch
Peer-reviewedYes