Hancock, RD
1992
Coherent Anti-Stokes Raman Spectroscopy (CARS) in Pulverized Coal Flames
Hancock, R.D.; Boyack, K.W. and Hedman, P.O.
Chapter 15, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium for Fossil Fuel Liquefaction, US Department of Energy and ACERC.
Coherent anti-Stokes Raman spectroscopy (CARS) is a diagnostic technique involving the use of high powered lasers to determine the temperature and concentration of the various major species found in combustion processes. This laser diagnostic technique allows in situ temperature and species concentration measurements to be obtained without disturbing the flame, as would most traditional thermocouples and sampling devices. Furthermore, there is no temperature limit associated with CARS because it is purely an optical technique.
CARS was first introduced by Taran and his co-workers at ONERA in France and was quickly recognized by other researchers throughout the world as a valuable diagnostic technique. Soon, numerous theoretical discussions, innovations, and practical applications of the CARS technique were introduced to the scientific community. CARS research has been implemented by various laboratories in the United States, Canada, England, France, Germany, Japan, and the Soviet Union.
Initially, CARS was applied to clean gas flames. However, as the instrument evolved, its diagnostic strengths were used to probe increasingly complex combustion environments. One such complex environment is that created by the introduction of particles into gas flames. Several researchers have studied such particle-laden flames and found them more difficult to probe, with the resulting CARS spectra more complex to analyze. These researchers have demonstrated that CARS measurements are possible in particle-laden flames.
Particle-laden flames are more difficult to probe because the particles attenuate the laser beams and can induce breakdown. Attenuation of the laser beams results in a loss of beam and signal strength. Breakdown alters the shape and intensity of the experimental spectra. The focus of this study was to develop methods by which consistent CARS measurements could be made on a regular basis in laboratory-scale particle-laden flames with coal loadings similar to those encountered in industrial burners.
This study extended the existing CARS instrument capability at Brigham Young University to a new laminar flame reactor that was designed to study flame speeds in pulverized coal flames. The facility modifications required the CARS laser beams to be transmitted over a 23-meter path length from the optical table to the reactor. The CARS signal was returned from the test chamber to the spectrometer with a fiber optic cable. The CARS signals were analyzed employing a modified version of the fitting code FTCARS from Sandia National Laboratories, using temperature and concentration libraries calculated with the CARS spectra code developed at Mississippi State University.
1991
Coherent Anti-Stokes Raman Spectroscopy (CARS) Measurements in Coal-Seeded Flames
Hancock, R.D.; Hedman, P.O. and Kramer, S.K.
Combustion and Flame, 87:77-88, 1991. Funded by ACERC.
Coherent anti-Stokes Raman spectroscopy (CARS) is a laser diagnostic technique that can be used to determine temperature and major species concentrations in harsh combustion environments. CARS has been successfully applied to clean gas flames, but much less attention has been given to particle-laden flames like those encountered in industrial coal burners. Typically, experimental CARS spectra are obtained from a flame and then compared with theoretical CARS spectra to determine temperature and species concentration information. This information is more difficult to acquire in coal flames due to background and nonresonant interferences. These interferences alter the shape and intensity of the CARS signal, thus making analysis with unmodified version of standard CARS fitting codes impractical. Nitrogen temperature measurements were obtained in heavily coal-seeded natural gas/air flames. Two different coals and several coal feed rates and stoichiometries were investigated in order to determine possible limits associated with making CARS measurements in coal flames. Carbon monoxide signals were observed in some of the fuel-rich coal-seed flames but the signals were weak and of poor quality, therefore, quantitative results are not reported. Temperature measurements were obtained with nonresonant background levels caused by particle-induced breakdown as high as 100% of the peak N2 resonant signal. CARS N2 temperatures generally agreed with equilibrium code calculations.
1989
Coherent Anti-Stokes Raman Spectroscopy (CARS) Temperature and Species Concentration Measurements in Coal-Seeded Flames
Hancock, R.D.; Hedman, P.O. and Kramer, S.K.
AIChE Annual Meeting, San Francisco, California, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Coherent anti-Stokes Raman Spectroscopy (CARS) is a laser diagnostic technique that can be used to determine temperature and major species concentrations in harsh combustion environments. CARS has been applied to clean gas flames with great success, but very little research has been conducted in particle-laden flames like those encountered in industrial coal burners. Typically, experimental CARS spectra are obtained from a flame and then compared to theoretical CARS spectra to determine temperature and species concentration information. This information is more difficult to acquire in coal flames due to the increased luminosity and enhanced background caused by particle and gas breakdown. The increased luminosity and breakdown alter the shape and intensity of the CARS signal, thus making analysis with unmodified versions of standard CARS fitting codes more complex.
CARS temperature and CO concentration measurements were obtained in heavily coal-seeded natural gas/air flames. Two different coals and several coal feed rates and stoichiometries were investigated in order to determine possible limits associated with making CARS measurements in coal flames. Temperature measurements were obtained with nonresonant background levels caused by particle-induced breakdown as high as 100% of the peak N2 resonant signal. CO concentration measurements deduced from the CO CARS spectra were less precise due to the difficulties of interpreting the CO CARS spectra in the presence of the enhanced background. Results generally agreed with thermochemical equilibrium combustion code calculations.
Hancock, RD
1992
Coherent Anti-Stokes Raman Spectroscopy (CARS) in Pulverized Coal Flames
Hancock, R.D.; Boyack, K.W. and Hedman, P.O.
Chapter 15, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium for Fossil Fuel Liquefaction, US Department of Energy and ACERC.
Coherent anti-Stokes Raman spectroscopy (CARS) is a diagnostic technique involving the use of high powered lasers to determine the temperature and concentration of the various major species found in combustion processes. This laser diagnostic technique allows in situ temperature and species concentration measurements to be obtained without disturbing the flame, as would most traditional thermocouples and sampling devices. Furthermore, there is no temperature limit associated with CARS because it is purely an optical technique.
CARS was first introduced by Taran and his co-workers at ONERA in France and was quickly recognized by other researchers throughout the world as a valuable diagnostic technique. Soon, numerous theoretical discussions, innovations, and practical applications of the CARS technique were introduced to the scientific community. CARS research has been implemented by various laboratories in the United States, Canada, England, France, Germany, Japan, and the Soviet Union.
Initially, CARS was applied to clean gas flames. However, as the instrument evolved, its diagnostic strengths were used to probe increasingly complex combustion environments. One such complex environment is that created by the introduction of particles into gas flames. Several researchers have studied such particle-laden flames and found them more difficult to probe, with the resulting CARS spectra more complex to analyze. These researchers have demonstrated that CARS measurements are possible in particle-laden flames.
Particle-laden flames are more difficult to probe because the particles attenuate the laser beams and can induce breakdown. Attenuation of the laser beams results in a loss of beam and signal strength. Breakdown alters the shape and intensity of the experimental spectra. The focus of this study was to develop methods by which consistent CARS measurements could be made on a regular basis in laboratory-scale particle-laden flames with coal loadings similar to those encountered in industrial burners.
This study extended the existing CARS instrument capability at Brigham Young University to a new laminar flame reactor that was designed to study flame speeds in pulverized coal flames. The facility modifications required the CARS laser beams to be transmitted over a 23-meter path length from the optical table to the reactor. The CARS signal was returned from the test chamber to the spectrometer with a fiber optic cable. The CARS signals were analyzed employing a modified version of the fitting code FTCARS from Sandia National Laboratories, using temperature and concentration libraries calculated with the CARS spectra code developed at Mississippi State University.
1991
Coherent Anti-Stokes Raman Spectroscopy (CARS) Measurements in Coal-Seeded Flames
Hancock, R.D.; Hedman, P.O. and Kramer, S.K.
Combustion and Flame, 87:77-88, 1991. Funded by ACERC.
Coherent anti-Stokes Raman spectroscopy (CARS) is a laser diagnostic technique that can be used to determine temperature and major species concentrations in harsh combustion environments. CARS has been successfully applied to clean gas flames, but much less attention has been given to particle-laden flames like those encountered in industrial coal burners. Typically, experimental CARS spectra are obtained from a flame and then compared with theoretical CARS spectra to determine temperature and species concentration information. This information is more difficult to acquire in coal flames due to background and nonresonant interferences. These interferences alter the shape and intensity of the CARS signal, thus making analysis with unmodified version of standard CARS fitting codes impractical. Nitrogen temperature measurements were obtained in heavily coal-seeded natural gas/air flames. Two different coals and several coal feed rates and stoichiometries were investigated in order to determine possible limits associated with making CARS measurements in coal flames. Carbon monoxide signals were observed in some of the fuel-rich coal-seed flames but the signals were weak and of poor quality, therefore, quantitative results are not reported. Temperature measurements were obtained with nonresonant background levels caused by particle-induced breakdown as high as 100% of the peak N2 resonant signal. CARS N2 temperatures generally agreed with equilibrium code calculations.
1989
Coherent Anti-Stokes Raman Spectroscopy (CARS) Temperature and Species Concentration Measurements in Coal-Seeded Flames
Hancock, R.D.; Hedman, P.O. and Kramer, S.K.
AIChE Annual Meeting, San Francisco, California, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Coherent anti-Stokes Raman Spectroscopy (CARS) is a laser diagnostic technique that can be used to determine temperature and major species concentrations in harsh combustion environments. CARS has been applied to clean gas flames with great success, but very little research has been conducted in particle-laden flames like those encountered in industrial coal burners. Typically, experimental CARS spectra are obtained from a flame and then compared to theoretical CARS spectra to determine temperature and species concentration information. This information is more difficult to acquire in coal flames due to the increased luminosity and enhanced background caused by particle and gas breakdown. The increased luminosity and breakdown alter the shape and intensity of the CARS signal, thus making analysis with unmodified versions of standard CARS fitting codes more complex.
CARS temperature and CO concentration measurements were obtained in heavily coal-seeded natural gas/air flames. Two different coals and several coal feed rates and stoichiometries were investigated in order to determine possible limits associated with making CARS measurements in coal flames. Temperature measurements were obtained with nonresonant background levels caused by particle-induced breakdown as high as 100% of the peak N2 resonant signal. CO concentration measurements deduced from the CO CARS spectra were less precise due to the difficulties of interpreting the CO CARS spectra in the presence of the enhanced background. Results generally agreed with thermochemical equilibrium combustion code calculations.