High-speed CH2O PLIF imaging in turbulent flames using a pulse-burst laser system
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In this manuscript, we demonstrate high-speed (10-kHz-acquisition rate) planar laser-induced fluorescence (PLIF) imaging of formaldehyde (CH2O) in turbulent non-premixed flames. Using the unique pulse-burst laser system (PBLS) at Ohio State University, high-energy laser pulses (∼100 mJ/pulse) at 355 nm with 100 μs pulse separation are generated and used to measure the time-varying CH2O distributions in attached and lifted methane-based turbulent flames. By taking advantage of the tunable, narrow spectral linewidth of the PBLS at 355 nm, the laser output can be frequency-tuned and adjusted to overlap with absorption “peaks” within the tail of the A–X transition of CH2O near 355 nm, thus increasing the acquired signal by as much as a factor of three. The reported signal-to-noise ratio (SNR) exceeds 55, which represents one of the highest SNR reported to date for kilohertz-rate imaging of scalars for comparable spatial resolution. Potential applications and pairings with other diagnostic approaches for high-speed reaction rate and multi-scalar imaging also are discussed.