Flame front visualization in highly turbulent jet flames using CH3 photofragmentation laser-induced fluorescence

Flame front visualization using methyl photofragmentation laser-induced fluorescence (CH3-PF-LIF) was demonstrated in turbulent premixed methane/air flames. A pump–probe method was used to detect CH3, where CH3 was first photolyzed to CH (X2П) fragments using a pump laser (212.8 nm), and the fragments were subsequently excited to CH in the C2Σ+ state by a probe laser at 314.4 nm. By detecting fluorescence from CH (C-X), instantaneous two-dimensional flame front imaging with a high signal-to-noise (SNR) ratio was achieved in fuel-lean and turbulent flames. A laser excitation scan was conducted to ensure that the detection of CH3 did not interfere with the other emissions. Visualization using CH3-PF-LIF was compared with visualization with conventional CH planar laser-induced fluorescence (CH-PLIF). The SNR of CH3-PF-LIF imaging is almost ten times higher than those of CH-PLIF, and flame front visualization using CH3-PF-LIF shows more topological structures than CH-PLIF in fuel-lean and highly turbulent flames