Simultaneous planar laser-induced fluorescence of nitric oxide and hydroxyl radical with a single dye laser in hydrogen flames

Simultaneous, planar laser-induced fluorescence (PLIF) of nitric oxide (NO) and hydroxyl radical (OH) is evidenced with a single dye laser and two intensified CCD (ICCD) cameras. The technique is demonstrated on three premixed turbulent hydrogen-air flames, at atmospheric conditions, with several laser excitation wavelengths within the A²Σ⁺ − X²Π (0,0) and A²Σ⁺ − X²Π (1,0) vibrational bands of NO and OH, respectively. Via adjustments of the grating angle of the dye laser, the output wavelengths can be optimized so that both LIF signals are obtained simultaneously, or it can be tuned to reach the most common excitation wavelengths for OH-PLIF (i.e., near 283 or 284 nm) or NO-PLIF (i.e., 225 and 226 nm) alternatively. The flame visualization results, obtained with the different excitation strategies, are consistent for the three flame conditions and enable to characterize both the reaction zones and the nitric oxide formation. With appropriate selection of the wavelength pair, the technique shows its great potential to enhance the ability of existing lasers to simultaneously visualize and quantify distributions of two key species in reacting flows with only a single laser.