Boyack, KW
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.
1990
Multiple Species Coherent Anti-Stokes Raman Spectroscopy (CARS) in Turbulent Jet Flames
Boyack, K.W.
Ninth International Congress on Applications of Lasers and Electro-Optics: Symposium on Optical Methods in Flow and Particle Diagnostics, Boston, Massachusetts, 1990. Funded by Kevin Boyack and ACERC.
Several multi-color CARS approaches have been recently demonstrated. One of these approaches, dual-Stokes CARS, is a straight-forward addition of two single-color CARS processes. This approach has been used to take simultaneous single-pulse measurements of temperature and mass fractions of N2, CO, O2 and CO2 in turbulent nonpremixed jet flames of CO/N2. The simultaneous measurement of all major species allows the nonresonant susceptibility of the mixture to be calculated directly rather than assumed, thus eliminating a potential source of error in the measurements. The measurement of all major species also allows calculation of the mixture fraction, defined as the local mass fraction of fluid originating from the primary stream. Direct measurement of the mixture fraction is very useful as it is necessary for the accurate modeling of turbulent reacting flows.
The accuracy of the Brigham Young University dual-Stokes CARS instrument has been determined by performing calibration measurements over flat flames of CO/N2 of known composition. This has shown that measurement of four species using CARS is possible and sufficiently accurate to justify use of the technique in the characterization of turbulent flames. Measurements were then taken in turbulent nonpremixed jet flames of the same fuel, which directly demonstrate the applicability of the instrument to turbulent reacting flows. A sample of data from more extensive measurements in turbulent nonpremixed jet flames is also given to show the extent to which multiple species CARS has been employed.
Dual-Stokes CARS System for Simultaneous Measurement of Temperature and Multiple Species in Turbulent Flames
Boyack, K.W. and Hedman, P.O.
Twenty-third Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 1990. Funded by ACERC.
A dual-Stokes coherent anti-Stokes Raman scattering (CARS) instrument has been used to make simultaneous time- and space-resolved measurements of temperature and the mass fractions of N2, CO, O2, and CO2. Calculation of the mixture fraction, a conserved scalar, is possible for each data point, making the technique useful in turbulent combustion environments. The viability of this instrumental approach has been demonstrated by calibrations in laminar CO/N2 flat flames of many different stoichiometries. Maximum single-shot rms values due to instrument fluctuations are attained in near stoichiometric mixtures and are ±45 K for temperature, ±0.042 for YN2 and YCO2, ±0.015 for YO2 and YCO, and ±0.036 for mixture fraction.
Measurements have been made using this instrument in turbulent nonpremixed jet flames of CO/N2 with small amounts of H2. These measurements demonstrated that for turbulent systems, limitations are imposed on the CARS technique due to insufficient dynamic range and image persistence problems with the intensified photodiode array (IPDA) detector. These limitations are minimized with proper experimental parameters and data correction methods.
1989
Measurements of Instantaneous Flame Properties in Turbulent Non-Premixed Jet Flames of CO/N2 Using Coherent Anti-Stokes Raman Spectroscopy (CARS)
Boyack, K.W. and Hedman, P.O.
Western States Section, The Combustion Institute, Livermore, California, 1989. (Also presented as a poster at the 1989 Gordon Conference on the Physics and Chemistry of Laser Diagnostics in Combustion, Plymouth, New Hampshire). Funded by ACERC (National Science Foundation and Associates and Affiliates).
The Coherent anti-Stokes Raman Scattering (CARS) technique has been used to make simultaneous time- and space-resolved measurements of temperature and the mass fractions of N2, CO, O2, and CO2. Calculation of the mixture fraction, x, conserved scalar, is possible for each data point, making the technique useful in turbulent combustion environments. The viability of this instrumental approach was demonstrated by calibrations in CO/N2 flat flames of many different stoichiometries. Maximum single-shot rms of fluctuations are attained in near stoichiometric mixtures and are estimated to be ±45 K for temperature, ±0.042 for YN2 and YCO2, ±0.015 for YO2 and YCO, and ±0.036 for mixture fraction.
Measurements have been made using this instrument in turbulent nonpremixed jet flames of ~70% CO / 30% N2 with various amounts of H2 ranging from zero to 2.8%. Local extinction has been seen to occur as the H2 content is reduced, until the entire flame is extinguished. This extinction is thought to be due to insufficient radical concentrations, thus inhibiting chain-branching steps in the wet CO oxidation mechanism.
Boyack, KW
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.
1990
Multiple Species Coherent Anti-Stokes Raman Spectroscopy (CARS) in Turbulent Jet Flames
Boyack, K.W.
Ninth International Congress on Applications of Lasers and Electro-Optics: Symposium on Optical Methods in Flow and Particle Diagnostics, Boston, Massachusetts, 1990. Funded by Kevin Boyack and ACERC.
Several multi-color CARS approaches have been recently demonstrated. One of these approaches, dual-Stokes CARS, is a straight-forward addition of two single-color CARS processes. This approach has been used to take simultaneous single-pulse measurements of temperature and mass fractions of N2, CO, O2 and CO2 in turbulent nonpremixed jet flames of CO/N2. The simultaneous measurement of all major species allows the nonresonant susceptibility of the mixture to be calculated directly rather than assumed, thus eliminating a potential source of error in the measurements. The measurement of all major species also allows calculation of the mixture fraction, defined as the local mass fraction of fluid originating from the primary stream. Direct measurement of the mixture fraction is very useful as it is necessary for the accurate modeling of turbulent reacting flows.
The accuracy of the Brigham Young University dual-Stokes CARS instrument has been determined by performing calibration measurements over flat flames of CO/N2 of known composition. This has shown that measurement of four species using CARS is possible and sufficiently accurate to justify use of the technique in the characterization of turbulent flames. Measurements were then taken in turbulent nonpremixed jet flames of the same fuel, which directly demonstrate the applicability of the instrument to turbulent reacting flows. A sample of data from more extensive measurements in turbulent nonpremixed jet flames is also given to show the extent to which multiple species CARS has been employed.
Dual-Stokes CARS System for Simultaneous Measurement of Temperature and Multiple Species in Turbulent Flames
Boyack, K.W. and Hedman, P.O.
Twenty-third Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 1990. Funded by ACERC.
A dual-Stokes coherent anti-Stokes Raman scattering (CARS) instrument has been used to make simultaneous time- and space-resolved measurements of temperature and the mass fractions of N2, CO, O2, and CO2. Calculation of the mixture fraction, a conserved scalar, is possible for each data point, making the technique useful in turbulent combustion environments. The viability of this instrumental approach has been demonstrated by calibrations in laminar CO/N2 flat flames of many different stoichiometries. Maximum single-shot rms values due to instrument fluctuations are attained in near stoichiometric mixtures and are ±45 K for temperature, ±0.042 for YN2 and YCO2, ±0.015 for YO2 and YCO, and ±0.036 for mixture fraction.
Measurements have been made using this instrument in turbulent nonpremixed jet flames of CO/N2 with small amounts of H2. These measurements demonstrated that for turbulent systems, limitations are imposed on the CARS technique due to insufficient dynamic range and image persistence problems with the intensified photodiode array (IPDA) detector. These limitations are minimized with proper experimental parameters and data correction methods.
1989
Measurements of Instantaneous Flame Properties in Turbulent Non-Premixed Jet Flames of CO/N2 Using Coherent Anti-Stokes Raman Spectroscopy (CARS)
Boyack, K.W. and Hedman, P.O.
Western States Section, The Combustion Institute, Livermore, California, 1989. (Also presented as a poster at the 1989 Gordon Conference on the Physics and Chemistry of Laser Diagnostics in Combustion, Plymouth, New Hampshire). Funded by ACERC (National Science Foundation and Associates and Affiliates).
The Coherent anti-Stokes Raman Scattering (CARS) technique has been used to make simultaneous time- and space-resolved measurements of temperature and the mass fractions of N2, CO, O2, and CO2. Calculation of the mixture fraction, x, conserved scalar, is possible for each data point, making the technique useful in turbulent combustion environments. The viability of this instrumental approach was demonstrated by calibrations in CO/N2 flat flames of many different stoichiometries. Maximum single-shot rms of fluctuations are attained in near stoichiometric mixtures and are estimated to be ±45 K for temperature, ±0.042 for YN2 and YCO2, ±0.015 for YO2 and YCO, and ±0.036 for mixture fraction.
Measurements have been made using this instrument in turbulent nonpremixed jet flames of ~70% CO / 30% N2 with various amounts of H2 ranging from zero to 2.8%. Local extinction has been seen to occur as the H2 content is reduced, until the entire flame is extinguished. This extinction is thought to be due to insufficient radical concentrations, thus inhibiting chain-branching steps in the wet CO oxidation mechanism.