2D Methyl Radical Measurement in a Methane/Air Flame at Atmospheric Pressure

摘要

2D measurements of methyl radicals (CH_3) in CH_4/air flames at atmospheric pressure have been achieved using coherent microwave Rayleigh scattering from Resonance Enhanced Multi-Photon Ionization, Radar REMPI. Relative direct measurements of the methyl radicals were conducted by Radar REMPI via the two-photon resonance of the intermediate state and subsequent one-photon ionization. Because of the proximity of the argon resonance state of 2s~22p~54f [7/2, J=4] (4+1 REMPI by 332.5nm) with the CH_3 state (2+1 REMPI by 333.6nm), in situ calibration with argon was performed to quantify the absolute concentration of CH_3. The REMPI cross sections of CH3 and argon were calculated based on time-dependent quantum perturbation theory. The Radar REMPI method has shown great flexibility for spatial scanning, large signal to noise ratio for measurements at atmospheric pressures, and significant potential to be generalized in a straightforward manner for quantitative measurements of other radicals and intermediate species in practical and relevant combustion environments.