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3027997 
Journal Article 
In situ H2O and temperature detection close to burning biomass pellets using calibration-free wavelength modulation spectroscopy 
Qu, Z; Schmidt, FM 
2015 
Yes 
Applied Physics B
ISSN: 0946-2171
EISSN: 1432-0649 
119 
1 
45-53 
WOS:000352292500007 
The design and application of an H2O/temperature sensor based on scanned calibration-free wavelength modulation spectroscopy (CF-WMS) and a single tunable diode laser at 1.4 A mu m is presented. The sensor probes two H2O absorption peaks in a single scan and simultaneously retrieves H2O concentration and temperature by least-squares fitting simulated 1f-normalized 2f-WMS spectra to measured 2f/1f-WMS signals, with temperature, concentration and nonlinear modulation amplitude as fitting parameters. Given a minimum detectable absorbance of 1.7 x 10(-5) cm(-1) Hz(-1/2), the system is applicable down to an H2O concentration of 0.1 % at 1,000 K and 20 cm path length (200 ppm center dot m). The temperature in a water-seeded laboratory-scale reactor (670-1220 K at 4 % H2O) was determined within an accuracy of 1 % by comparison with the reactor thermocouple. The CF-WMS sensor was applied to real time in situ measurements of H2O concentration and temperature time histories (0.25-s time resolution) in the hot gases 2-11 mm above biomass pellets during atmospheric combustion in the reactor. Temperatures between 1,200 and 1,600 K and H2O concentrations up to 40 % were detected above the biofuels.