Flame temperature measurements by radar resonance-enhanced multiphoton ionization of molecular oxygen

摘要

Here we report nonintrusive local rotational temperature measurements of molecular oxygen, based on coherent microwave scattering (radar) from resonance-enhanced multiphoton ionization (REMPI) in room air and hydrogen/air flames. Analyses of the rotational line strengths of the two-photon molecular oxygen C~3Π(v = 2) ← X~3Σ(v' = 0) transition have been used to determine the hyperfine rotational state distribution of the ground X~3Σ(v' = 0) state. Rotationally resolved 2 + 1 REMPI spectra of the molecular oxygen C~3Π(v = 2) ← X~3Σ(v' = 0) transition at different temperatures were obtained experimentally by radar REMPI. Rotational temperatures have been determined from the resulting Boltzmann plots. The measurements in general had an accuracy of ～ ±60 K in the hydrogen/air flames at various equivalence ratios. Discussions about the decreased accuracy for the temperature measurement at elevated temperatures have been presented.