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Turbulence and combustion interaction: High resolution local flame front structure visualization using simultaneous single-shot PLIF imaging of CH, OH, and CH2O in a piloted premixed jet flame

Li, Zhongshan LU ; Li, Bo LU ; Sun, Zhiwei LU ; Bai, Xue-Song LU and Aldén, Marcus LU (2010) In Combustion and Flame 157(6). p.1087-1096
Abstract
High resolution planar laser-induced fluorescence (PLIF) was applied to investigate the local flame front structures of turbulent premixed methane/air jet flames in order to reveal details about turbulence and flame interaction. The targeted turbulent flames were generated on a specially designed coaxial jet burner, in which low speed stoichiometric gas mixture was fed through the outer large tube to provide a laminar pilot flame for stabilization of the high speed jet flame issued through the small inner tube. By varying the inner tube flow speed and keeping the mixture composition as that of the outer tube, different flames were obtained covering both the laminar and turbulent flame regimes with different turbulent intensities.... (More)
High resolution planar laser-induced fluorescence (PLIF) was applied to investigate the local flame front structures of turbulent premixed methane/air jet flames in order to reveal details about turbulence and flame interaction. The targeted turbulent flames were generated on a specially designed coaxial jet burner, in which low speed stoichiometric gas mixture was fed through the outer large tube to provide a laminar pilot flame for stabilization of the high speed jet flame issued through the small inner tube. By varying the inner tube flow speed and keeping the mixture composition as that of the outer tube, different flames were obtained covering both the laminar and turbulent flame regimes with different turbulent intensities. Simultaneous CH/CH2O, and also OH PLIF images were recorded to characterize the influence of turbulence eddies on the reaction zone structure, with a spatial resolution of about 40 mu m and temporal resolution of around 10 ns. Under all experimental conditions, the CH radicals were found to exist only in a thin layer; the CH2O were found in the inner flame whereas the OH radicals were seen in the outer flame with the thin CH layer separating the OH and CH2O layers. The outer OH layer is thick and it corresponds to the oxidation zone and post-flame zone; the CH2O layer is thin in laminar flows; it becomes broad at high speed turbulent flow conditions. This phenomenon was analyzed using chemical kinetic calculations and eddy/flame interaction theory. It appears that under high turbulence intensity conditions, the small eddies in the preheat zone can transport species such as CH2O from the reaction zones to the preheat zone. The CH2O species are not consumed in the preheat zone due to the absence of H, O, and OH radicals by which CH2O is to be oxidized. The CH radicals cannot exist in the preheat zone due to the rapid reactions of this species with O-2 and CO2 in the inner-layer of the reaction zones. The local PLIF intensities were evaluated using an area integrated PLIF signal. Substantial increase of the CH2O signal and decrease of CH signal was observed as the jet velocity increases. These observations raise new challenges to the current flamelet type models. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
broadening, Flame, Jet flame, Turbulence flame interaction, CH2O, PLIF, CH
in
Combustion and Flame
volume
157
issue
6
pages
1087 - 1096
publisher
Elsevier
external identifiers
  • wos:000276599600005
  • scopus:77950341098
ISSN
0010-2180
DOI
10.1016/j.combustflame.2010.02.017
language
English
LU publication?
yes
id
1a158597-f7aa-454f-bab1-c5c3941d49d6 (old id 1603189)
date added to LUP
2010-05-17 15:23:00
date last changed
2018-07-08 03:43:53
@article{1a158597-f7aa-454f-bab1-c5c3941d49d6,
  abstract     = {High resolution planar laser-induced fluorescence (PLIF) was applied to investigate the local flame front structures of turbulent premixed methane/air jet flames in order to reveal details about turbulence and flame interaction. The targeted turbulent flames were generated on a specially designed coaxial jet burner, in which low speed stoichiometric gas mixture was fed through the outer large tube to provide a laminar pilot flame for stabilization of the high speed jet flame issued through the small inner tube. By varying the inner tube flow speed and keeping the mixture composition as that of the outer tube, different flames were obtained covering both the laminar and turbulent flame regimes with different turbulent intensities. Simultaneous CH/CH2O, and also OH PLIF images were recorded to characterize the influence of turbulence eddies on the reaction zone structure, with a spatial resolution of about 40 mu m and temporal resolution of around 10 ns. Under all experimental conditions, the CH radicals were found to exist only in a thin layer; the CH2O were found in the inner flame whereas the OH radicals were seen in the outer flame with the thin CH layer separating the OH and CH2O layers. The outer OH layer is thick and it corresponds to the oxidation zone and post-flame zone; the CH2O layer is thin in laminar flows; it becomes broad at high speed turbulent flow conditions. This phenomenon was analyzed using chemical kinetic calculations and eddy/flame interaction theory. It appears that under high turbulence intensity conditions, the small eddies in the preheat zone can transport species such as CH2O from the reaction zones to the preheat zone. The CH2O species are not consumed in the preheat zone due to the absence of H, O, and OH radicals by which CH2O is to be oxidized. The CH radicals cannot exist in the preheat zone due to the rapid reactions of this species with O-2 and CO2 in the inner-layer of the reaction zones. The local PLIF intensities were evaluated using an area integrated PLIF signal. Substantial increase of the CH2O signal and decrease of CH signal was observed as the jet velocity increases. These observations raise new challenges to the current flamelet type models. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.},
  author       = {Li, Zhongshan and Li, Bo and Sun, Zhiwei and Bai, Xue-Song and Aldén, Marcus},
  issn         = {0010-2180},
  keyword      = {broadening,Flame,Jet flame,Turbulence flame interaction,CH2O,PLIF,CH},
  language     = {eng},
  number       = {6},
  pages        = {1087--1096},
  publisher    = {Elsevier},
  series       = {Combustion and Flame},
  title        = {Turbulence and combustion interaction: High resolution local flame front structure visualization using simultaneous single-shot PLIF imaging of CH, OH, and CH2O in a piloted premixed jet flame},
  url          = {http://dx.doi.org/10.1016/j.combustflame.2010.02.017},
  volume       = {157},
  year         = {2010},
}