Abstract

Imaging detection of methyl radicals has been performed in laminar premixed methane-air flames at atmospheric pressure. A nanosecond Q-switched neodymium-doped yttrium aluminum garnet (Nd : YAG) laser was employed to provide the fifth-harmonic-generated 212.8 nm laser beam. The intense ultraviolet (UV) laser pulse was sent through the flame front to photodissociate the methyl (CH₃) radicals in the reaction zone of the flames stabilized on a piloted jet flame burner. The emission spectra from the photodissociated fragments were collected using an imaging spectrometer with the flame-front structure spatially resolved. Combining the spatial and spectral information, we recognized that the emission from the (A-X) methine (CH) transitions located at 431 nm was generated from the CH₃ photolysis and could be used to visualize the distribution of CH₃ radicals. With proper filtering, the high-power UV laser (around 15 mJ/pulse) provided by the compact Nd : YAG laser makes it possible to visualize CH₃ distribution naturally generated in the reaction zone of laminar methane-air premixed flames.

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