Pump-probe strategy for instantaneous 2D detection of CH in flames using a single laser.

Visualization of the reaction zone of flames using CH radicals as markers is restricted by the low concentration of CH in fuel-lean conditions. To address this, methyl radicals () are employed as a substitution of CH in premixed methane/air flames. A pump-probe method was adopted with the pump laser photolyzing and the probe laser detecting the photolyzed CH () fragments. Laser excitation scans were performed to ensure that the fluorescence detected was from CH only. Visualization of the reaction zone of flames was accomplished by a photofragmentation laser-induced fluorescence technique in fuel-lean conditions (the equivalence ratio of 0.4), where CH planar laser-induced fluorescence did not work in both laminar and turbulent jet flames. The proposed pump-probe method of can be used to visualize the reaction zone of hydrocarbon combustion under both fuel-lean and fuel-rich conditions with a superior signal-to-noise ratio.