Simultaneous sensing of temperature, CO, and CO2 in a scramjet combustor using quantum cascade laser absorption spectroscopy
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A mid-infrared laser absorption sensor was developed for gas temperature and carbon oxide (CO, CO2) concentrations in high-enthalpy, hydrocarbon combustion flows. This diagnostic enables non-intrusive, in situ measurements in harsh environments produced by hypersonic propulsion ground test facilities. The sensing system utilizes tunable quantum cascade lasers capable of probing the fundamental mid-infrared absorption bands of CO and CO2 in the 4–5 µm wavelength domain. A scanned-wavelength direct absorption technique was employed with two lasers, one dedicated to each species, free-space fiber-coupled using a bifurcated hollow-core fiber for remote light delivery on a single line of sight. Scanned-wavelength modulation spectroscopy with second-harmonic detection was utilized to extend the dynamic range of the CO measurement. The diagnostic was field-tested on a direct-connect scramjet combustor for ethylene–air combustion. Simultaneous, laser-based measurements of carbon monoxide and carbon dioxide provide a basis for evaluating combustion completion or efficiency with temporal and spatial resolution in practical hydrocarbon-fueled engines.
KeywordsCarbon Oxide Quantum Cascade Laser Wavelength Modulation Spectroscopy Scramjet Combustor Combustion Progress
This work was sponsored by the National Center for Hypersonic Combined Cycle Propulsion (NCHCCP), Grant FA 9550-09-1-0611, with technical monitors Chiping Li (AFOSR) and Rick Gaffney (NASA). The authors would also like to thank Bob Rockwell, Brian Rice, and Roger Reynolds of the University of Virginia for their assistance in operating the UVaSCF facility.
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