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Laser-Based Techniques for Combustion Diagnostics

Georgiev, Nikola LU (1997)
Abstract
Two-photon-induced Degenerate Four-Wave Mixing, DFWM, was applied for the first time to the detection of CO, and NH3 molecules. Measurements were performed in a cell, and in atmospheric-pressure flames. In the cell measurements, the signal dependence on the pressure and on the laser beam intensity was studied. The possibility of simultaneous detection of NH3 and OH was investigated. Carbon monoxide and ammonia were also detected employing two-photon-induced Polarization Spectroscopy, PS. In the measurements performed in a cold gas flow, the signal strength dependence on the laser intensity, and on the polarization of the pump beam, was investigated. In the case of CO, the signal dependence on the number density of CO in the presence of He... (More)
Two-photon-induced Degenerate Four-Wave Mixing, DFWM, was applied for the first time to the detection of CO, and NH3 molecules. Measurements were performed in a cell, and in atmospheric-pressure flames. In the cell measurements, the signal dependence on the pressure and on the laser beam intensity was studied. The possibility of simultaneous detection of NH3 and OH was investigated. Carbon monoxide and ammonia were also detected employing two-photon-induced Polarization Spectroscopy, PS. In the measurements performed in a cold gas flow, the signal strength dependence on the laser intensity, and on the polarization of the pump beam, was investigated. In the case of CO, the signal dependence on the number density of CO in the presence of He and N2, was studied. In stable-flame investigations, one dimensional images of the studied species, collected at different heights above the burner, were combined in order to produce two dimensional maps of the species distributions in the flame. Signals from one-, and two-photon polarisation spectroscopy from OH and NH3, were detected simultaneously. The spectrum of the CO molecule was measured at different temperatures. An approach to improve the spatial resolution of the Amplified Stimulated Emission, ASE, was developed. In this approach, two laser beams at different frequencies were crossed in the sample. If the sum of the frequencies of the two laser beams matches a two-photon resonance of the investigated species, only the molecules in the intersection volume will be excited. NH3 molecules and C atoms were studied. The potential of using two-photon LIF for two-dimensional imaging of combustion species was investigated. Applying this technique, NH3, CO, and H, and O atoms were detected spatially resolved. In the case of CO imaging, efforts were made to separate the CO emission from the emission originating from unresonantly excited C2. Detection limits for some of the species are discussed. Although LIF is species specific, several species can be detected simultaneously by utilizing spectral coincidences. Combining one-, and two-photon process, OH, NO, and O were detected simultaneously, as well as OH, NO, and NH3. The temperature dependencies of the involved transitions are discussed. Collisional quenching is the major source of uncertainty in quantitative applications of LIF. A technique for two-dimensional, absolute species concentration measurements, circumventing the problems associated with collisional quenching, was developed. By applying simple mathematics to the ratio of two LIF signals generated from two counterpropagating laser beams, the absolute species concentration could be obtained. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Dr Ewart, Paul
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Physics, LIF, Laser-based diagnostic techniques, PS, DFWM, Fysik, Fysicumarkivet A:1997:Georgiev
pages
160 pages
publisher
Division of Combustion Physics, Department of Physics, Lund University
defense location
Sal B, Fysiska Institutionen
defense date
1997-05-21 10:15
external identifiers
  • Other:ISRN: LUTFD2/TFCP- -28- -SE
language
English
LU publication?
yes
id
7b0788cb-24b8-490e-9e67-c6087ea2d6f0 (old id 29250)
date added to LUP
2007-06-14 10:33:21
date last changed
2016-09-19 08:45:13
@misc{7b0788cb-24b8-490e-9e67-c6087ea2d6f0,
  abstract     = {Two-photon-induced Degenerate Four-Wave Mixing, DFWM, was applied for the first time to the detection of CO, and NH3 molecules. Measurements were performed in a cell, and in atmospheric-pressure flames. In the cell measurements, the signal dependence on the pressure and on the laser beam intensity was studied. The possibility of simultaneous detection of NH3 and OH was investigated. Carbon monoxide and ammonia were also detected employing two-photon-induced Polarization Spectroscopy, PS. In the measurements performed in a cold gas flow, the signal strength dependence on the laser intensity, and on the polarization of the pump beam, was investigated. In the case of CO, the signal dependence on the number density of CO in the presence of He and N2, was studied. In stable-flame investigations, one dimensional images of the studied species, collected at different heights above the burner, were combined in order to produce two dimensional maps of the species distributions in the flame. Signals from one-, and two-photon polarisation spectroscopy from OH and NH3, were detected simultaneously. The spectrum of the CO molecule was measured at different temperatures. An approach to improve the spatial resolution of the Amplified Stimulated Emission, ASE, was developed. In this approach, two laser beams at different frequencies were crossed in the sample. If the sum of the frequencies of the two laser beams matches a two-photon resonance of the investigated species, only the molecules in the intersection volume will be excited. NH3 molecules and C atoms were studied. The potential of using two-photon LIF for two-dimensional imaging of combustion species was investigated. Applying this technique, NH3, CO, and H, and O atoms were detected spatially resolved. In the case of CO imaging, efforts were made to separate the CO emission from the emission originating from unresonantly excited C2. Detection limits for some of the species are discussed. Although LIF is species specific, several species can be detected simultaneously by utilizing spectral coincidences. Combining one-, and two-photon process, OH, NO, and O were detected simultaneously, as well as OH, NO, and NH3. The temperature dependencies of the involved transitions are discussed. Collisional quenching is the major source of uncertainty in quantitative applications of LIF. A technique for two-dimensional, absolute species concentration measurements, circumventing the problems associated with collisional quenching, was developed. By applying simple mathematics to the ratio of two LIF signals generated from two counterpropagating laser beams, the absolute species concentration could be obtained.},
  author       = {Georgiev, Nikola},
  keyword      = {Physics,LIF,Laser-based diagnostic techniques,PS,DFWM,Fysik,Fysicumarkivet A:1997:Georgiev},
  language     = {eng},
  pages        = {160},
  publisher    = {ARRAY(0x8d2e080)},
  title        = {Laser-Based Techniques for Combustion Diagnostics},
  year         = {1997},
}