High-speed CH2O PLIF imaging in turbulent flames using a pulse-burst laser system
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.
Acknowledgment is made to the Air Force Office of Scientific Research (Julian Tishkoff/Chiping Li—Technical Monitors) and to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. The authors acknowledge previous financial support from NASA (Paul Danehy—Technical Monitor), the U.S. Air Force Research Laboratory—Propulsion Directorate (James Gord—Technical Monitor), the Air Force Office of Scientific Research (J. Schmisseur—Technical Monitor), and the National Science Foundation Major Research Instrumentation program for the development of the pulse-burst laser system. KNG acknowledges support from the Department of Energy (DOE) Office of Science Graduate Fellowship Program administered by the Oak Ridge Institute for Science and Education for the DOE.
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