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Rotational Coherent Anti-Stokes Raman Spectroscopy: Experimental and Theoretical Developments in Gas-phase Thermometry

Afzelius, Mikael LU (2004)
Abstract
Dual-broadband pure rotational coherent anti-Stokes Raman spectroscopy was investigated in terms of thermometry and species concentration measurement for studies of combustion.



The modelling of rotational CARS spectra under conditions of high pressure at room temperature was investigated. Resonant terms of the Stokes (CSRS) type were found to have a significant effect on the intensity of the anti-Stokes (CARS) branch, the effect increasing in strength with an increase in pressure. Taking account of this inter-branch interference effect improved the accuracy of temperature measurement under conditions of high pressure.



An experimental study of the statistical precision of temperature measurements showed... (More)
Dual-broadband pure rotational coherent anti-Stokes Raman spectroscopy was investigated in terms of thermometry and species concentration measurement for studies of combustion.



The modelling of rotational CARS spectra under conditions of high pressure at room temperature was investigated. Resonant terms of the Stokes (CSRS) type were found to have a significant effect on the intensity of the anti-Stokes (CARS) branch, the effect increasing in strength with an increase in pressure. Taking account of this inter-branch interference effect improved the accuracy of temperature measurement under conditions of high pressure.



An experimental study of the statistical precision of temperature measurements showed the precision to improve with use of a single-mode rather than a multi-mode Nd:YAG laser, a decrease in standard deviation by a factor of two or more being observed. Further investigation linked the measurement precision to the intensity noise observed in the CARS spectra.



Temperature measurements in the post-flame zone of ethylene/air flames were conducted with the aim of studying the impact on temperature measurements of the collisional line widths employed in the model. Taking account of the line broadening of the species CO, CO<sub>2</sub> and H<sub>2</sub>O was found to increase the evaluated temperature by 20-47 K. Spectra recorded in ethylene/air flames revealed the spectral signatures of N<sub>2</sub>, O<sub>2</sub>, CO and CO<sub>2</sub>, the spectrum of nitrogen always being strongest. The potential of rotational CARS for species concentration measurements under such conditions was also investigated. A model for binary mixtures of N<sub>2</sub> and CO that was developed was tested for concentration measurements in these flames. The measured CO concentrations agreed closely with theoretical calculations.



The collisional line broadening of Raman spectral lines in mixtures of N<sub>2</sub> and CO was studied theoretically by means of semiclassical Robert-Bonamy calculations. The self-broadening of nitrogen (N<sub>2</sub>-N<sub>2</sub>) in particular was investigated, employing the ab initio intermolecular potential PES8. The major objective was to calculate CO-N<sub>2</sub> and N<sub>2</sub>-CO line broadening. Use of the line widths obtained resulted in more accurate CO concentration measurements in binary mixtures of CO and N<sub>2</sub> by use of rotational CARS. (Less)
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author
opponent
  • Professor Ewart, Paul, University of Oxford, United Kingdom
organization
publishing date
type
Thesis
publication status
published
subject
keywords
collision line-broadening calculations, combustion laser diagnostics, Laserteknik, Laser technology, CARS, coherent laser spectroscopy, Fysicumarkivet A:2004:Afzelius
pages
230 pages
publisher
Division of Combustion Physics, Department of Physics, Lund University
defense location
Fysiska Institutionen, Professorsgatan 1, Hörsal B, Lunds Tekniska Högskola.
defense date
2004-09-03 10:15
external identifiers
  • other:ISRN:LUTFD2/TFCP--94--SE
ISSN
1102-8718
ISBN
91-628-6179-4
language
English
LU publication?
yes
id
353e16b1-bf43-4782-ae1f-fd3f2ffd3213 (old id 467224)
date added to LUP
2007-09-25 19:42:29
date last changed
2016-09-19 08:44:58
@phdthesis{353e16b1-bf43-4782-ae1f-fd3f2ffd3213,
  abstract     = {Dual-broadband pure rotational coherent anti-Stokes Raman spectroscopy was investigated in terms of thermometry and species concentration measurement for studies of combustion.<br/><br>
<br/><br>
The modelling of rotational CARS spectra under conditions of high pressure at room temperature was investigated. Resonant terms of the Stokes (CSRS) type were found to have a significant effect on the intensity of the anti-Stokes (CARS) branch, the effect increasing in strength with an increase in pressure. Taking account of this inter-branch interference effect improved the accuracy of temperature measurement under conditions of high pressure.<br/><br>
<br/><br>
An experimental study of the statistical precision of temperature measurements showed the precision to improve with use of a single-mode rather than a multi-mode Nd:YAG laser, a decrease in standard deviation by a factor of two or more being observed. Further investigation linked the measurement precision to the intensity noise observed in the CARS spectra.<br/><br>
<br/><br>
Temperature measurements in the post-flame zone of ethylene/air flames were conducted with the aim of studying the impact on temperature measurements of the collisional line widths employed in the model. Taking account of the line broadening of the species CO, CO&lt;sub&gt;2&lt;/sub&gt; and H&lt;sub&gt;2&lt;/sub&gt;O was found to increase the evaluated temperature by 20-47 K. Spectra recorded in ethylene/air flames revealed the spectral signatures of N&lt;sub&gt;2&lt;/sub&gt;, O&lt;sub&gt;2&lt;/sub&gt;, CO and CO&lt;sub&gt;2&lt;/sub&gt;, the spectrum of nitrogen always being strongest. The potential of rotational CARS for species concentration measurements under such conditions was also investigated. A model for binary mixtures of N&lt;sub&gt;2&lt;/sub&gt; and CO that was developed was tested for concentration measurements in these flames. The measured CO concentrations agreed closely with theoretical calculations.<br/><br>
<br/><br>
The collisional line broadening of Raman spectral lines in mixtures of N&lt;sub&gt;2&lt;/sub&gt; and CO was studied theoretically by means of semiclassical Robert-Bonamy calculations. The self-broadening of nitrogen (N&lt;sub&gt;2&lt;/sub&gt;-N&lt;sub&gt;2&lt;/sub&gt;) in particular was investigated, employing the ab initio intermolecular potential PES8. The major objective was to calculate CO-N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;-CO line broadening. Use of the line widths obtained resulted in more accurate CO concentration measurements in binary mixtures of CO and N&lt;sub&gt;2&lt;/sub&gt; by use of rotational CARS.},
  author       = {Afzelius, Mikael},
  isbn         = {91-628-6179-4},
  issn         = {1102-8718},
  keyword      = {collision line-broadening calculations,combustion laser diagnostics,Laserteknik,Laser technology,CARS,coherent laser spectroscopy,Fysicumarkivet A:2004:Afzelius},
  language     = {eng},
  pages        = {230},
  publisher    = {Division of Combustion Physics, Department of Physics, Lund University},
  school       = {Lund University},
  title        = {Rotational Coherent Anti-Stokes Raman Spectroscopy: Experimental and Theoretical Developments in Gas-phase Thermometry},
  year         = {2004},
}