Temperature and water concentration measurements in combustion gases using a DFB diode laser at 1.4 μm

A sensor using a single DFB diode laser at 1.4 μm based on wavelength modulation spectroscopy for the measurements of the gas temperature and the H2O concentration in combustion gases is developed. A line pair of H2O absorption transitions located at 7085.251 and 7085.876 cm−1 is selected based on some design rules. The 1f normalized 2f method is used to remove the need for the calibration and to correct for the transmission variation due to beam steering, mechanical misalignments, soot, and window fouling. The precision for the temperature and H2O concentration measurements are 1.05 and 2.10% in a controlled static cell, respectively. Burner experiments demonstrate the ability of the system for in situ measurements.