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Investigation of OH and CH2O distributions at ultra-high repetition rates by planar laser induced fluorescence imaging in highly turbulent jet flames

Wang, Zhenkan LU ; Stamatoglou, Panagiota LU ; Zhou, Bo LU ; Aldén, Marcus LU ; Bai, Xue Song LU and Richter, Mattias LU (2018) In Fuel 234. p.1528-1540
Abstract

For better understanding of the transient behavior of the flow/flame interaction in highly turbulent premixed flames, measurement techniques with sufficient temporal resolution are required. Using a burst-mode laser pumped optical parametric oscillator system, the present work demonstrated an ultra-high-speed diagnostic, for the first time, capable of visualizing hydroxyl radicals (OH) and formaldehyde (CH2O) distributions in a highly turbulent flame at repetition rates up to 140 kHz (i.e. with a temporal resolution of 7.1 μs) to access the Kolmogorov time scales of flames in the distributed/broken reaction zone regime (Ka ≥ 100). More than 100 consecutive images were recorded in the present work for OH planar laser induced... (More)

For better understanding of the transient behavior of the flow/flame interaction in highly turbulent premixed flames, measurement techniques with sufficient temporal resolution are required. Using a burst-mode laser pumped optical parametric oscillator system, the present work demonstrated an ultra-high-speed diagnostic, for the first time, capable of visualizing hydroxyl radicals (OH) and formaldehyde (CH2O) distributions in a highly turbulent flame at repetition rates up to 140 kHz (i.e. with a temporal resolution of 7.1 μs) to access the Kolmogorov time scales of flames in the distributed/broken reaction zone regime (Ka ≥ 100). More than 100 consecutive images were recorded in the present work for OH planar laser induced fluorescence (PLIF) measurement at 100 kHz. Systematic temporal and spatial evolution of the flame structure is clearly resolved over long sequences, e.g. 1.2 ms for OH PLIF and 10 ms for CH2O PLIF respectively. The Kolmogorov time scale for all the cases at x/d = 10 and x/d = 30 are estimated with the minimum Kolmogorov time scale of 7.5 μs, indicating that nearly all time-scales of the flow are resolved with the present experimental setup. The axial velocity of the CH2O structure at its outer layer at different flame height positions, UCH2O, is obtained. The velocity UCH2O is compared with the LDV results, which shows a good agreement with the mean flow velocity. By comparing UCH2O with the local axial velocity, different mechanisms responsible for the large-scale wrinkle structures in the reaction zone and the propagation of CH2O structure along the flame height are discussed. Power spectral density and autocorrelation function based on the CH2O outer layer fluctuation in the radial direction are illustrated. Quantitative analysis of the ultra-high-speed diagnostics data further augments the understanding of turbulent combustion down to Kolmogorov scale experimentally.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Burst-mode laser, CHO, OH, Planar laser induced fluorescence, Turbulent jet flame, Ultra-high-speed diagnostics
in
Fuel
volume
234
pages
13 pages
publisher
Elsevier
external identifiers
  • scopus:85053140959
ISSN
0016-2361
DOI
10.1016/j.fuel.2018.07.012
language
English
LU publication?
yes
id
dc3ef7c1-34c7-4a66-bd79-39c2be243b76
date added to LUP
2018-10-08 10:44:13
date last changed
2019-02-20 11:29:51
@article{dc3ef7c1-34c7-4a66-bd79-39c2be243b76,
  abstract     = {<p>For better understanding of the transient behavior of the flow/flame interaction in highly turbulent premixed flames, measurement techniques with sufficient temporal resolution are required. Using a burst-mode laser pumped optical parametric oscillator system, the present work demonstrated an ultra-high-speed diagnostic, for the first time, capable of visualizing hydroxyl radicals (OH) and formaldehyde (CH<sub>2</sub>O) distributions in a highly turbulent flame at repetition rates up to 140 kHz (i.e. with a temporal resolution of 7.1 μs) to access the Kolmogorov time scales of flames in the distributed/broken reaction zone regime (Ka ≥ 100). More than 100 consecutive images were recorded in the present work for OH planar laser induced fluorescence (PLIF) measurement at 100 kHz. Systematic temporal and spatial evolution of the flame structure is clearly resolved over long sequences, e.g. 1.2 ms for OH PLIF and 10 ms for CH<sub>2</sub>O PLIF respectively. The Kolmogorov time scale for all the cases at x/d = 10 and x/d = 30 are estimated with the minimum Kolmogorov time scale of 7.5 μs, indicating that nearly all time-scales of the flow are resolved with the present experimental setup. The axial velocity of the CH<sub>2</sub>O structure at its outer layer at different flame height positions, U<sub>CH2O</sub>, is obtained. The velocity U<sub>CH2O</sub> is compared with the LDV results, which shows a good agreement with the mean flow velocity. By comparing U<sub>CH2O</sub> with the local axial velocity, different mechanisms responsible for the large-scale wrinkle structures in the reaction zone and the propagation of CH<sub>2</sub>O structure along the flame height are discussed. Power spectral density and autocorrelation function based on the CH<sub>2</sub>O outer layer fluctuation in the radial direction are illustrated. Quantitative analysis of the ultra-high-speed diagnostics data further augments the understanding of turbulent combustion down to Kolmogorov scale experimentally.</p>},
  author       = {Wang, Zhenkan and Stamatoglou, Panagiota and Zhou, Bo and Aldén, Marcus and Bai, Xue Song and Richter, Mattias},
  issn         = {0016-2361},
  keyword      = {Burst-mode laser,CHO,OH,Planar laser induced fluorescence,Turbulent jet flame,Ultra-high-speed diagnostics},
  language     = {eng},
  month        = {12},
  pages        = {1528--1540},
  publisher    = {Elsevier},
  series       = {Fuel},
  title        = {Investigation of OH and CH<sub>2</sub>O distributions at ultra-high repetition rates by planar laser induced fluorescence imaging in highly turbulent jet flames},
  url          = {http://dx.doi.org/10.1016/j.fuel.2018.07.012},
  volume       = {234},
  year         = {2018},
}