Abstract
Spatially resolved quantitative measurements of methyl radicals (CH3) in CH4/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 \( 3p^{2} A_{2}^{\prime \prime } 0_{0}^{0} \) state and subsequent one-photon ionization. Due to the proximity of the argon resonance state of 2s 22p 54f [7/2, J = 4](4+1 REMPI by 332.5 nm) with the CH3 state of \( 3p^{2} A_{2}^{\prime \prime } 0_{0}^{0} \) (2+1 REMPI by 333.6 nm), in situ calibration with argon was performed to quantify the absolute concentration of CH3. The REMPI cross sections of CH3 and argon were calculated based on time-dependent quantum perturbation theory. The measured CH3 concentration in CH4/air flames was in good agreement with numerical simulations performed using detailed chemical kinetics. 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 straightforwardly generalized for the quantitative measurements of other radicals and intermediate species in practical and relevant combustion environments.
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Acknowledgments
The work at the University of Tennessee Knoxville was supported by NSF CBET-1032523. We also thank Dr. James R. Gord, Dr. Sukesh Roy and Dr. Hans Stauffer at the Air Force Research Laboratory for insightful discussions with regard to multiphoton ionization.
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Wu, Y., Zhang, Z., Ombrello, T.M. et al. Quantitative Radar REMPI measurements of methyl radicals in flames at atmospheric pressure. Appl. Phys. B 111, 391–397 (2013). https://doi.org/10.1007/s00340-013-5345-1
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DOI: https://doi.org/10.1007/s00340-013-5345-1
Keywords
- Flame Front
- Burner Surface
- Liftoff Height
- Fuel Tube
- Detailed Chemical Kinetic