Planar laser-induced imaging of CH3 for high resolution single-shot reaction-zone visualization in premixed methane/air flames over broad stoichiometric ratios
(2022) In Combustion and Flame 243.- Abstract
We report a novel approach for single-shot planar imaging of CH3 radicals in premixed methane and air flames. A 213 nm beam from the 5th harmonic of an Nd:YAG laser was resonantly absorbed by the CH3 radicals, which were excited to the highly pre-dissociative upper level and dissociated to H2 and CH (X), as the main dissociation channel. The CH radicals were consequently excited by a 388 nm beam from an alexandrite laser, and the fluorescence from the excited CH radicals was collected off-resonant at 431 nm. Using this Photo-Fragmentation Planar Laser-Induced Fluorescence (PF-PLIF) technique, instantaneous flame front structures, represented by CH3 radicals, can be visualized with high spatial... (More)
We report a novel approach for single-shot planar imaging of CH3 radicals in premixed methane and air flames. A 213 nm beam from the 5th harmonic of an Nd:YAG laser was resonantly absorbed by the CH3 radicals, which were excited to the highly pre-dissociative upper level and dissociated to H2 and CH (X), as the main dissociation channel. The CH radicals were consequently excited by a 388 nm beam from an alexandrite laser, and the fluorescence from the excited CH radicals was collected off-resonant at 431 nm. Using this Photo-Fragmentation Planar Laser-Induced Fluorescence (PF-PLIF) technique, instantaneous flame front structures, represented by CH3 radicals, can be visualized with high spatial resolution over a broad range of stoichiometric ratios. Signal-to-noise ratios up to 50 were observed for premixed methane/air flame with stoichiometric ratio as low as 0.26. The CH radicals naturally presented in flame front are more than 400 times lower in concentration than the CH3 radicals in premixed methane/air flames even at the conditions close to stoichiometric or slightly fuel rich cases where the highest CH concentrations exist, and the CH3/CH concentration ratios increase dramatically moving towards fuel lean conditions. By adopting a structured illumination of the 213 nm pump beam, the naturally presented CH radicals were visualized simultaneously with CH3 at slightly fuel rich laminar flames, where the CH signal intensity was 5 times lower than that from CH3. The results indicate that the CH3 PF-PLIF technique can provide much stronger signal than the CH PLIF and presented a much promising potential for applications in fuel-lean flames. Finally, the CH3 PF-PLIF was performed in premixed turbulent flames to demonstrate the feasibility of this technique for flame front visualization in turbulent premixed flames.
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- author
- Gao, Jinlong LU ; Fan, Qingshuang LU ; Liu, Xin LU ; Li, Bo LU ; Kristinsson, Elias ; Aldén, Marcus LU and Li, Zhongshan LU
- organization
- publishing date
- 2022-09
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- CH, Methyl radical, PF-PLIF, Turbulent premixed flame
- in
- Combustion and Flame
- volume
- 243
- article number
- 112361
- pages
- 7 pages
- publisher
- Elsevier
- external identifiers
-
- scopus:85138190517
- ISSN
- 0010-2180
- DOI
- 10.1016/j.combustflame.2022.112361
- language
- English
- LU publication?
- yes
- additional info
- Publisher Copyright: © 2022
- id
- b6b4c9b2-ec0a-4101-9e88-3c25df9ab806
- date added to LUP
- 2022-10-14 08:57:09
- date last changed
- 2023-11-21 12:10:43
@article{b6b4c9b2-ec0a-4101-9e88-3c25df9ab806,
abstract = {{<p>We report a novel approach for single-shot planar imaging of CH<sub>3</sub> radicals in premixed methane and air flames. A 213 nm beam from the 5th harmonic of an Nd:YAG laser was resonantly absorbed by the CH<sub>3</sub> radicals, which were excited to the highly pre-dissociative upper level and dissociated to H<sub>2</sub> and CH (X), as the main dissociation channel. The CH radicals were consequently excited by a 388 nm beam from an alexandrite laser, and the fluorescence from the excited CH radicals was collected off-resonant at 431 nm. Using this Photo-Fragmentation Planar Laser-Induced Fluorescence (PF-PLIF) technique, instantaneous flame front structures, represented by CH<sub>3</sub> radicals, can be visualized with high spatial resolution over a broad range of stoichiometric ratios. Signal-to-noise ratios up to 50 were observed for premixed methane/air flame with stoichiometric ratio as low as 0.26. The CH radicals naturally presented in flame front are more than 400 times lower in concentration than the CH<sub>3</sub> radicals in premixed methane/air flames even at the conditions close to stoichiometric or slightly fuel rich cases where the highest CH concentrations exist, and the CH<sub>3</sub>/CH concentration ratios increase dramatically moving towards fuel lean conditions. By adopting a structured illumination of the 213 nm pump beam, the naturally presented CH radicals were visualized simultaneously with CH<sub>3</sub> at slightly fuel rich laminar flames, where the CH signal intensity was 5 times lower than that from CH<sub>3</sub>. The results indicate that the CH<sub>3</sub> PF-PLIF technique can provide much stronger signal than the CH PLIF and presented a much promising potential for applications in fuel-lean flames. Finally, the CH<sub>3</sub> PF-PLIF was performed in premixed turbulent flames to demonstrate the feasibility of this technique for flame front visualization in turbulent premixed flames.</p>}},
author = {{Gao, Jinlong and Fan, Qingshuang and Liu, Xin and Li, Bo and Kristinsson, Elias and Aldén, Marcus and Li, Zhongshan}},
issn = {{0010-2180}},
keywords = {{CH; Methyl radical; PF-PLIF; Turbulent premixed flame}},
language = {{eng}},
publisher = {{Elsevier}},
series = {{Combustion and Flame}},
title = {{Planar laser-induced imaging of CH<sub>3</sub> for high resolution single-shot reaction-zone visualization in premixed methane/air flames over broad stoichiometric ratios}},
url = {{http://dx.doi.org/10.1016/j.combustflame.2022.112361}},
doi = {{10.1016/j.combustflame.2022.112361}},
volume = {{243}},
year = {{2022}},
}