Quantitative laser-induced fluorescence of CH in atmospheric pressure flames

J Luque, RJH Klein-Douwel, JB Jeffries, P Smith*, DR Crosley

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

3 Citations (Scopus)

Abstract

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 quasilinear laser-induced fluorescence scheme. The peak number density was (1.0 +/- 0.4) x 10(13) cm(-3) or 2.4 +/-1 ppm at 1900 K, with a flame-front width of 250 mum (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
Number of pages12
JournalApplied Physics B: Lasers and Optics
Volume75
Issue number6-7
DOIs
Publication statusPublished - Nov-2002
Externally publishedYes

Keywords

  • ABSOLUTE CONCENTRATION MEASUREMENTS
  • ROTATIONAL ENERGY-TRANSFER
  • INDUCED PREDISSOCIATIVE FLUORESCENCE
  • INDUCED SATURATED FLUORESCENCE
  • CAVITY RINGDOWN SPECTROSCOPY
  • DEPOSITING DC-ARCJET
  • ABSORPTION-SPECTROSCOPY
  • RAYLEIGH-SCATTERING
  • TEMPERATURE-MEASUREMENTS
  • CONCENTRATION PROFILES

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