Simultaneous Burst Imaging of Dual Species Using Planar Laser-Induced Fluorescence at 50 kHz in Turbulent Premixed Flames.

Spatially and temporally resolved measurements are of great importance in turbulent premixed flame studies, especially when investigating rapid processes such as when flame local extinction, re-ignition, or flashback occur in a reacting flow. Here, an experimental approach for simultaneously probing two different species at high frame rates (50 kHz) is presented by employing a multi-YAG laser system. The laser radiation at 355 nm generated by a multi-YAG laser system was split into two beam paths: one beam for exciting formaldehyde and the other for pumping an optical parametric oscillator (OPO). To be able to capture the resulting fluorescence at such a high frame rate without significant loss in spatial resolution, two framing cameras, containing a total of 16 intensified charge-coupled devices (CCDs), were employed. In principle, the proposed setup provides the possibility of probing formaldehyde and simultaneously accessing the distribution of one other relevant species at this high frame rate. In this demonstration, the laser wavelength was tuned to 283 nm and, in conjunction with the 355 nm beam path, simultaneously high speed two-dimensional (2D) visualization of OH-radicals and formaldehyde was achieved. A modified flat flame, McKenna-type burner was used to provide a turbulent premixed jet-flame supported by a surrounding pilot flame. Local flame extinction and re-ignition processes were recorded for fuel/air jet speeds of 120 m/s.