Coherent anti-stokes raman spectroscopy (CARS) measurements in coal-seeded flames

Abstract

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 measurementw 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 N 2 resonant signal. CARS N 2 temperatures generally agreed with equilibrium code calculations.