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Laser-Induced Photofragmentation Fluorescence Imaging of Alkali Compounds in Flames

Leffler, Tomas LU ; Brackmann, Christian LU ; Aldén, Marcus LU and Li, Zhongshan LU (2017) In Applied Spectroscopy 71(6). p.1289-1299
Abstract

Laser-induced photofragmentation fluorescence has been investigated for the imaging of alkali compounds in premixed laminar methane–air flames. An ArF excimer laser, providing pulses of wavelength 193 nm, was used to photodissociate KCl, KOH, and NaCl molecules in the post-flame region and fluorescence from the excited atomic alkali fragment was detected. Fluorescence emission spectra showed distinct lines of the alkali atoms allowing for efficient background filtering. Temperature data from Rayleigh scattering measurements together with simulations of potassium chemistry presented in literature allowed for conclusions on the relative contributions of potassium species KOH and KCl to the detected signal. Experimental approaches for... (More)

Laser-induced photofragmentation fluorescence has been investigated for the imaging of alkali compounds in premixed laminar methane–air flames. An ArF excimer laser, providing pulses of wavelength 193 nm, was used to photodissociate KCl, KOH, and NaCl molecules in the post-flame region and fluorescence from the excited atomic alkali fragment was detected. Fluorescence emission spectra showed distinct lines of the alkali atoms allowing for efficient background filtering. Temperature data from Rayleigh scattering measurements together with simulations of potassium chemistry presented in literature allowed for conclusions on the relative contributions of potassium species KOH and KCl to the detected signal. Experimental approaches for separate measurements of these components are discussed. Signal power dependence and calculated fractions of dissociated molecules indicate the saturation of the photolysis process, independent on absorption cross-section, under the experimental conditions. Quantitative KCl concentrations up to 30 parts per million (ppm) were evaluated from the fluorescence data and showed good agreement with results from ultraviolet absorption measurements. Detection limits for KCl photofragmentation fluorescence imaging of 0.5 and 1.0 ppm were determined for averaged and single-shot data, respectively. Moreover, simultaneous imaging of KCl and NaCl was demonstrated using a stereoscope with filters. The results indicate that the photofragmentation method can be employed for detailed studies of alkali chemistry in laboratory flames for validation of chemical kinetic mechanisms crucial for efficient biomass fuel utilization.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
alkali, chlorides, Combustion, fluorescence, hydroxides, imaging, photofragmentation
in
Applied Spectroscopy
volume
71
issue
6
pages
11 pages
publisher
Society for Applied Spectroscopy
external identifiers
  • scopus:85019630216
  • wos:000402001600021
ISSN
0003-7028
DOI
10.1177/0003702816681010
language
English
LU publication?
yes
id
8e949017-c5aa-4279-9002-1a393a58b236
date added to LUP
2017-06-08 13:00:16
date last changed
2018-03-04 05:02:30
@article{8e949017-c5aa-4279-9002-1a393a58b236,
  abstract     = {<p>Laser-induced photofragmentation fluorescence has been investigated for the imaging of alkali compounds in premixed laminar methane–air flames. An ArF excimer laser, providing pulses of wavelength 193 nm, was used to photodissociate KCl, KOH, and NaCl molecules in the post-flame region and fluorescence from the excited atomic alkali fragment was detected. Fluorescence emission spectra showed distinct lines of the alkali atoms allowing for efficient background filtering. Temperature data from Rayleigh scattering measurements together with simulations of potassium chemistry presented in literature allowed for conclusions on the relative contributions of potassium species KOH and KCl to the detected signal. Experimental approaches for separate measurements of these components are discussed. Signal power dependence and calculated fractions of dissociated molecules indicate the saturation of the photolysis process, independent on absorption cross-section, under the experimental conditions. Quantitative KCl concentrations up to 30 parts per million (ppm) were evaluated from the fluorescence data and showed good agreement with results from ultraviolet absorption measurements. Detection limits for KCl photofragmentation fluorescence imaging of 0.5 and 1.0 ppm were determined for averaged and single-shot data, respectively. Moreover, simultaneous imaging of KCl and NaCl was demonstrated using a stereoscope with filters. The results indicate that the photofragmentation method can be employed for detailed studies of alkali chemistry in laboratory flames for validation of chemical kinetic mechanisms crucial for efficient biomass fuel utilization.</p>},
  author       = {Leffler, Tomas and Brackmann, Christian and Aldén, Marcus and Li, Zhongshan},
  issn         = {0003-7028},
  keyword      = {alkali,chlorides,Combustion,fluorescence,hydroxides,imaging,photofragmentation},
  language     = {eng},
  month        = {06},
  number       = {6},
  pages        = {1289--1299},
  publisher    = {Society for Applied Spectroscopy},
  series       = {Applied Spectroscopy},
  title        = {Laser-Induced Photofragmentation Fluorescence Imaging of Alkali Compounds in Flames},
  url          = {http://dx.doi.org/10.1177/0003702816681010},
  volume       = {71},
  year         = {2017},
}