Flame Temperatures from Vibrational Raman Scattering

  • Marshall Lapp


Raman scattering signatures are functionally dependent upon temperature, and are therefore useful as diagnostic probes. Various Raman scattering techniques for the measurement of temperature are outlined here. Those methods based upon rotational molecular structure are then briefly discussed in order to compare and contrast them with the ones based upon vibrational structure. For flame gases, the elevated temperatures and the multicomponent, variable composition make the vibrational scattering techniques appear to be more useful than those based upon pure rotational scattering. Temperature measurements based upon vibrational Raman scattering are described next, with an emphasis on the vibrational techniques developed in this laboratory. These techniques are based upon the spectral structure of the fundamental Stokes vibrational band series, which consists of the ground state band (initial → final molecular vibrational levels: v = 0 → v = 1) and the upper state or “hot” bands (1 → 2, 2 → 3, etc.).


Vibrational Level State Band Rotational Level Band Peak Ground State Band 
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    A possible exception to our conclusion that rotational Raman scattering is unsuitable for flame work is the interferonstric “comb” method of Dr. Barrett discussed earlier in these Proceedings. Here, a technique based upon use of a Fabry-Perot interferometer is described that has the capability of distinguishing rotational Raman signatures for dissimilar species. Utilization of this method on a high-temperature multi-component gas mixture for diagnostics of many species with roughly similar rotational constants (i.e., roughly similar rotational line spacings) will, no doubt, be difficult, but hopefully, will be possible. (See also “note added in proof” at the end of Section III, C.)Google Scholar
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    For nitrogen data, the steady stoichiometric hydrogen-air flame utilized flow rates of 37.5 cc/sec H2 and 88.8 cc/sec air, for which 65% of the product gases was nitrogen. Since the image of the monochromator entrance slits at the flame scattering position was about 5 mm high, an estimate was made of the temperature variation along this zone. This was found to be about 16°K. The reproducibility of the thermocouple data was about ± 1/2°K.Google Scholar
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    For hydrogen data, a somewhat unsteady fuel-rich (four-times-stoichiometric) hydrogen-air flame was used (79.3 cc/sec H2 and 47.0 cc/sec air) for which about 51% of the product gases was hydrogen. The variation of temperature with position along the slit image was much more severe than was the case for the stoichiometric flame, being roughly 110°K over a 5 mm vertical zone. Furthermore, the reproducibility was significantly poorer, being roughly ± 3°K. This flame, colored red from the emission of water vapor vibration-rotation bands [See A. G. Gaydon, Spectroscopy of Flames (Chapman and Hall, London, 1957), pp. 79, 90, and 241.] was subject to significantly more diffusion by the ambient atmosphere than the stoichiometric flame, which undoubtedly contributed to its less reproducible characteristics. It had, however, the virtue of a high hydrogen content.Google Scholar

Copyright information

© Springer Science+Business Media New York 1974

Authors and Affiliations

  • Marshall Lapp
    • 1
  1. 1.General Electric Corporate Research and DevelopmentSchenectadyUSA

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