Scanned-wavelength-modulation spectroscopy near 2.5 μm for H2O and temperature in a hydrocarbon-fueled scramjet combustor
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- Goldenstein, C.S., Schultz, I.A., Spearrin, R.M. et al. Appl. Phys. B (2014) 116: 717. doi:10.1007/s00340-013-5755-0
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The design and demonstration of a two-color tunable diode laser sensor for measurements of temperature and H2O in an ethylene-fueled model scramjet combustor are presented. This sensor probes multiple H2O transitions in the fundamental vibration bands near 2.5 μm that are up to 20 times stronger than those used by previous near-infrared H2O sensors. In addition, two design measures enabled high-fidelity measurements in the nonuniform flow field. (1) A recently developed calibration-free scanned-wavelength-modulation spectroscopy spectral-fitting strategy was used to infer the integrated absorbance of each transition without a priori knowledge of the absorption lineshape and (2) transitions with strengths that scale near-linearly with temperature were used to accurately determine the H2O column density and the H2O-weighted path-averaged temperature from the integrated absorbance of two transitions.