On the use of planar laser-induced fluorescence of polycyclic aromatic hydrocarbons (PAHs) in an ethylene/air laminar co-flow diffusion flame

The paper presents an experimental study of planar laser-induced fluorescence (LIF) of polycyclic aromatic hydrocarbons (PAHs) in an ethylene/air diffusion sooting flame stabilized on a Santoro-type burner. Laser-induced signals under 266 nm excitation were recorded at three spectral bands centered at 340 nm, 390 nm and 450 nm with different integration time of 3 ns, 10 ns and 50 ns, respectively. The distribution of PAHs within the sooting region and the dark zone between PAHs and soot were imaged with high spatial resolution. The results and detailed assessment are valuable for the use of LIF technique for PAH detection in sooting flames. It is found that different integration time used in the measurement can lead to significantly different results of the derived formation and consumption rates of PAHs. In addition, the images at 340 nm show an unexpected structure at the base of the flame, which might not be LIF signals from small PAHs. All results reveal that even though planar LIF is a simple and robust technique for PAH detection, it is necessary to carefully choose suitable detection spectral channel and integration time for signal collection.