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Show Paper No. 8 Coherent Anti-Stokes Raman Spectroscopy (CARS) Measurements In a Laminar Flame Coal Combustor * Robert D. Hancock, Kevin W. Boyack, and PaulO. Hedman Advanced Combustion Engineering Research Center, Brigham Young University Provo, Utah 84604 ABSTRACT Coherent Anti-Stokes Raman Spectroscopy (CARS) temperature measurements have been demonstrated in a coal-seeded natural gas flame. An incoherent addition of nonresonant background caused by particle induced gas breakdown was observed in the coal-seeded gas flame spectra. By properly accounting for this nonresonant addition, consistent temperature measurements can be obtained for coal-seeded flames. Corrected fit temperatures were found to be independent of the level of background in the individual spectra. No particle breakdown was observed in the spectra obtained for this study, but given higher coal feed rates and different laser energies such breakdown might be observed. Single shot temperature measurements were obtained in the coal-seeded gas flame. These single shot spectra were fit successfully for temperature when the background level was less than about 20% of the nitrogen peak. Error in fitting without background subtraction demonstrated a linear relationship to background level. With proper calibration, temperatures in coal-seeded flames can be determined by fitting without background subtraction. INTRODUCTION Coherent Anti-Stokes Raman Spectroscopy (CARS) is an optical technique that can provide in situ temperature and species concentration information in harsh corrbustion environments. CARS has been shown by many investigators to be an effective means of determining the temperature and species concentrations in clean gas flames, however, relatively few investigators (Alden and Wallin 1985, Beiting 1985, Greenhalgh 1983, Lucht 1988) have attempted to make extensive CARS measurements in particle laden environments such as those encountered in coal combustors. In coal flames, the temperature and species concentration information becomes more difficult to interpret due to an incoherent addition of nonresonant background caused by particle induced gas breakdown which follows the spectral prOfile of • This work was supported by the National Science Foundation through the Brigham Young University Advanced Combustion Engineering Research Center (ACERC). 1 |
