Towards Quantitative Flame Species Concentration Measurements Using Radar REMPI
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This paper details recent efforts aimed at the development of the Radar REMPI technique as a combustion diagnostic. Radar REMPI, which combines the benefits of coherent microwave scattering and the selective ionization capabilities of resonance enhanced multiphoton ionization (REMPI), has been largely successful when used to measure stable species concentrations under room temperature conditions. As an initial step to extending this diagnostic to a combustion system, a well studied methane/air flame over a Hencken burner under atmospheric conditions is seeded with varying trace amounts of an inert gas, Xenon. Our results show that under calibrated conditions, decent signal linearity with target species concentration down to 310 ppm is achievable. To account for the presence of multiple species expected in a flame, complementary experiments are conducted in a cell at room temperature to establish and isolate the effect of different buffer gases on the signal. The cell experiments suggest the existence of electron loss processes which take place on timescales that are not adequately captured by our detection system. These processes occur even at buffer species concentrations which are typical of that found in flames, and if neglected, can impact the accuracy of the measurement. Overall, these experiments augur well for the development of Radar REMPI as a combustion tool, and in particular the use of an inert gas as a calibration approach. However, significant efforts should continue to be directed at both identifying key flame species that may have a large influence on the electron loss rates as well as characterizing and improving the resolution of the detection system. 2013 by Princeton University.
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51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition
