Quantitative laser-induced fluorescence of CH in atmospheric pressure flames

J. Luque, R.J.H. Klein-Douwel, J.B. Jeffries, G.P. Smith, D.R. Crosley

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    3 Citations (Scopus)


    Absolute number densities of the CH radical were determined in a partially premixed methane/air flame (equivalence ratio was 1.36) at atmospheric pressure by exciting a predissociating level via the CH B–X(1,0) transition using a quasi-linear laser-induced fluorescence scheme. The peak number density was (1.0±0.4)×1013 cm-3 or 2.4±1 ppm at 1900 K, with a flame-front width of 250 µm (FWHM). Rotational energy transfer must be considered for correct laser-induced fluorescence signal interpretation. Competition between optical pumping and rotational relaxation in both excited and ground states produces a signal that varies almost linearly with laser pulse energy even for large pumping rates. For these conditions, the population of the initial ground-state rotational level is depleted by optical pumping, and rotational energy transfer collisions rapidly repopulate the level during the laser pulse. Deviations from linear behavior are less than 20%. The effects of spatial resolution and polarization of the fluorescence on the absolute measurements are also discussed.
    Original languageEnglish
    Pages (from-to)779-790
    JournalApplied Physics B: Lasers and Optics
    Issue number6-7
    Publication statusPublished - 2002


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