Investigation of local flame structures and statistics in partially premixed turbulent jet flames using simultaneous single-shot CH and OH planar laser-induced fluorescence imaging

Johannes Kiefer, Z. S. Li, J. Zetterberg, X. S. Bai, M. Alden

Research output: Contribution to journalArticle

73 Citations (Scopus)

Abstract

We report on the application of simultaneous single-shot imaging of CH and OH radicals using planar laser-induced fluorescence (PLIF) to investigate partially permixed turbulent jet flames. Various flames have been stabilized on a coaxial jet flame burner consisting of an outer and an inner tube of diameter 22 and 2.2 mm, respectively. From the outer tube a rich methane/air mixture was supplied at a relatively low flow velocity, while a jet of pure air was introduced from the inner one, resulting in a turbulent jet flame on top of a laminar pilot flame. The turbulence intensity was controlled by varying the inner jet flow speed from 0 up to 120 m/s, corresponding to a maximal Reynolds number of the inner jet airflow of 13,200. The CH/OH PLIF imaging clearly revealed the local structure of the studied flames. In the proximity of the burner, a two-layer reaction zone structure was identified where an inner zone characterized by strong CH signals has a typical structure of rich premixed flames. An outer reaction zone characterized by strong OH signals has a typical structure of a diffusion flame that oxidizes the intermediate fuels formed in the inner rich premixed flame. In the moderate-turbulence flow, the CH layers were very thin closed surfaces in the entire flame, whereas the OH layers were much thicker. In the high-intensity-turbulence flame, the CH layer remained thin until it vanished in the upper part of the flame, showing local extinction and reignition behavior of the flame. The single-shot PLIF images have been utilized to determine the flame surface density (FSD). In low and moderate turbulence intensity cases the FSDs determined from CH and OH agreed with each other, while in the highly turbulent case a locally broken CH layer was observed, leading to a significant difference in the FSD results determined via the OH and CH radicals. Furthermore, the means and the standard deviations of CH and OH radicals were obtained to provide statistical information about the flames that may be used for validation of numerical calculations. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Original languageEnglish
Pages (from-to)802-818
Number of pages17
JournalCombustion and Flame
Volume154
Issue number4
Early online date23 Apr 2008
DOIs
Publication statusPublished - 1 Sep 2008

Fingerprint

turbulent jets
turbulent flames
laser induced fluorescence
shot
flames
Fluorescence
Statistics
statistics
methylidyne
Imaging techniques
Lasers
Turbulence
Fuel burners
turbulence
premixed flames
burners
Methane
Air
Flow velocity
low turbulence

Keywords

  • partially premixed combustion
  • turbulent combustion
  • jet flame
  • planar laser-induced fluorescence
  • flame surfaqce density
  • CH
  • OH
  • Stokes-Raman scattering
  • dual-pump cars
  • reaction zone structure
  • Rayleigh scattering
  • Alexandrite laser
  • diffusion flames
  • PIV measurements
  • pressure flames
  • surface density
  • reacting flows

Cite this

Investigation of local flame structures and statistics in partially premixed turbulent jet flames using simultaneous single-shot CH and OH planar laser-induced fluorescence imaging. / Kiefer, Johannes; Li, Z. S.; Zetterberg, J.; Bai, X. S.; Alden, M.

In: Combustion and Flame, Vol. 154, No. 4, 01.09.2008, p. 802-818.

Research output: Contribution to journalArticle

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abstract = "We report on the application of simultaneous single-shot imaging of CH and OH radicals using planar laser-induced fluorescence (PLIF) to investigate partially permixed turbulent jet flames. Various flames have been stabilized on a coaxial jet flame burner consisting of an outer and an inner tube of diameter 22 and 2.2 mm, respectively. From the outer tube a rich methane/air mixture was supplied at a relatively low flow velocity, while a jet of pure air was introduced from the inner one, resulting in a turbulent jet flame on top of a laminar pilot flame. The turbulence intensity was controlled by varying the inner jet flow speed from 0 up to 120 m/s, corresponding to a maximal Reynolds number of the inner jet airflow of 13,200. The CH/OH PLIF imaging clearly revealed the local structure of the studied flames. In the proximity of the burner, a two-layer reaction zone structure was identified where an inner zone characterized by strong CH signals has a typical structure of rich premixed flames. An outer reaction zone characterized by strong OH signals has a typical structure of a diffusion flame that oxidizes the intermediate fuels formed in the inner rich premixed flame. In the moderate-turbulence flow, the CH layers were very thin closed surfaces in the entire flame, whereas the OH layers were much thicker. In the high-intensity-turbulence flame, the CH layer remained thin until it vanished in the upper part of the flame, showing local extinction and reignition behavior of the flame. The single-shot PLIF images have been utilized to determine the flame surface density (FSD). In low and moderate turbulence intensity cases the FSDs determined from CH and OH agreed with each other, while in the highly turbulent case a locally broken CH layer was observed, leading to a significant difference in the FSD results determined via the OH and CH radicals. Furthermore, the means and the standard deviations of CH and OH radicals were obtained to provide statistical information about the flames that may be used for validation of numerical calculations. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.",
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T1 - Investigation of local flame structures and statistics in partially premixed turbulent jet flames using simultaneous single-shot CH and OH planar laser-induced fluorescence imaging

AU - Kiefer, Johannes

AU - Li, Z. S.

AU - Zetterberg, J.

AU - Bai, X. S.

AU - Alden, M.

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N2 - We report on the application of simultaneous single-shot imaging of CH and OH radicals using planar laser-induced fluorescence (PLIF) to investigate partially permixed turbulent jet flames. Various flames have been stabilized on a coaxial jet flame burner consisting of an outer and an inner tube of diameter 22 and 2.2 mm, respectively. From the outer tube a rich methane/air mixture was supplied at a relatively low flow velocity, while a jet of pure air was introduced from the inner one, resulting in a turbulent jet flame on top of a laminar pilot flame. The turbulence intensity was controlled by varying the inner jet flow speed from 0 up to 120 m/s, corresponding to a maximal Reynolds number of the inner jet airflow of 13,200. The CH/OH PLIF imaging clearly revealed the local structure of the studied flames. In the proximity of the burner, a two-layer reaction zone structure was identified where an inner zone characterized by strong CH signals has a typical structure of rich premixed flames. An outer reaction zone characterized by strong OH signals has a typical structure of a diffusion flame that oxidizes the intermediate fuels formed in the inner rich premixed flame. In the moderate-turbulence flow, the CH layers were very thin closed surfaces in the entire flame, whereas the OH layers were much thicker. In the high-intensity-turbulence flame, the CH layer remained thin until it vanished in the upper part of the flame, showing local extinction and reignition behavior of the flame. The single-shot PLIF images have been utilized to determine the flame surface density (FSD). In low and moderate turbulence intensity cases the FSDs determined from CH and OH agreed with each other, while in the highly turbulent case a locally broken CH layer was observed, leading to a significant difference in the FSD results determined via the OH and CH radicals. Furthermore, the means and the standard deviations of CH and OH radicals were obtained to provide statistical information about the flames that may be used for validation of numerical calculations. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

AB - We report on the application of simultaneous single-shot imaging of CH and OH radicals using planar laser-induced fluorescence (PLIF) to investigate partially permixed turbulent jet flames. Various flames have been stabilized on a coaxial jet flame burner consisting of an outer and an inner tube of diameter 22 and 2.2 mm, respectively. From the outer tube a rich methane/air mixture was supplied at a relatively low flow velocity, while a jet of pure air was introduced from the inner one, resulting in a turbulent jet flame on top of a laminar pilot flame. The turbulence intensity was controlled by varying the inner jet flow speed from 0 up to 120 m/s, corresponding to a maximal Reynolds number of the inner jet airflow of 13,200. The CH/OH PLIF imaging clearly revealed the local structure of the studied flames. In the proximity of the burner, a two-layer reaction zone structure was identified where an inner zone characterized by strong CH signals has a typical structure of rich premixed flames. An outer reaction zone characterized by strong OH signals has a typical structure of a diffusion flame that oxidizes the intermediate fuels formed in the inner rich premixed flame. In the moderate-turbulence flow, the CH layers were very thin closed surfaces in the entire flame, whereas the OH layers were much thicker. In the high-intensity-turbulence flame, the CH layer remained thin until it vanished in the upper part of the flame, showing local extinction and reignition behavior of the flame. The single-shot PLIF images have been utilized to determine the flame surface density (FSD). In low and moderate turbulence intensity cases the FSDs determined from CH and OH agreed with each other, while in the highly turbulent case a locally broken CH layer was observed, leading to a significant difference in the FSD results determined via the OH and CH radicals. Furthermore, the means and the standard deviations of CH and OH radicals were obtained to provide statistical information about the flames that may be used for validation of numerical calculations. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

KW - partially premixed combustion

KW - turbulent combustion

KW - jet flame

KW - planar laser-induced fluorescence

KW - flame surfaqce density

KW - CH

KW - OH

KW - Stokes-Raman scattering

KW - dual-pump cars

KW - reaction zone structure

KW - Rayleigh scattering

KW - Alexandrite laser

KW - diffusion flames

KW - PIV measurements

KW - pressure flames

KW - surface density

KW - reacting flows

U2 - 10.1016/j.combustflame.2008.04.002

DO - 10.1016/j.combustflame.2008.04.002

M3 - Article

VL - 154

SP - 802

EP - 818

JO - Combustion and Flame

JF - Combustion and Flame

SN - 0010-2180

IS - 4

ER -