Absolute concentration measurements of atomic oxygen in a flame using radar REMPI
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abstract
This paper presents an extension of previous work aimed at developing radar REMPI as a combustion diagnostic. The absolute atomic oxygen concentration in a methane/air flame is measured via the use of a noble gas, xenon as a vehicle for calibration. The atomic oxygen concentration is varied by changing the equivalence ratio of the flame. Insight gained from a previous study has established xenon as a viable candidate for calibration. Xenon possesses a two-photon intermediate resonance which lies in close proximity to that of atomic oxygen and furthermore, good signal linearity with concentration in a flame has also been demonstrated. Implementation of this calibration scheme finds decent agreement with the expected equilibrium values under stoichiometric conditions but exceeds these numbers in the fuel rich and fuel lean regimes when the atomic oxygen concentration is an order of magnitude lower. Laser photolysis is examined as a possible reason for this disagreement and initial experiments suggest that molecular oxygen and carbon dioxide are two main photolytic precursors.
