Journal
PROCEEDINGS OF THE COMBUSTION INSTITUTE
Volume 35, Issue -, Pages 2155-2162Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.proci.2014.07.043
Keywords
Scramjet; Cavity flameholder; Supersonic combustion; Laser-induced breakdown
Funding
- American Society for Engineering Education (ASEE, through the Summer Faculty Fellowship Program)
- Air Force Research Laboratory (AFRL)
- Air Force Office of Scientific Research (AFOSR) [FA9550-12-1-0161]
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Laser-induced breakdown is used for quantitative gas property measurements (gas density and ethylene fuel concentration) in a cavity flameholder in a supersonic crossflow. A plasma is produced by a focused laser beam (Nd: YAG, 532 nm) in the cavity to measure gas properties at the location of the plasma and to ignite cavity flames. Plasma energy (PE), defined by the laser pulse energy absorbed/scattered in the plasma, and plasma emission spectra are recorded for estimating gas density and species concentration, respectively. To obtain correlations of PE vs. gas density and emission spectra vs. fuel concentration, calibration experiments are conducted using a variable-pressure (0-900 mbar)/temperature (300-900 K) chamber and a Hencken burner installed in a variable-pressure (50-900 mbar) combustion chamber. Total measurement time is sufficiently short, similar to 80 ns after laser arrival at the plasma region, to capture the high intensity portion of the emission and to minimize effects of plasma displacement (in the high-speed flow). Specifically, the laser pulse energy incident and transmitted (through the plasma) are measured, and the plasma emission spectra are captured during a 50-ns gate, after an approximate 30-ns time delay (relative to onset of emission from the plasma volume) to avoid strong background emission from the plasma. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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