Line-of-sight absorption of water vapor: Gas temperature sensing in uniform and nonuniform flows

Line-of-sight (LOS) laser absorption spectroscopy provides a non-intrusive, fast, sensitive and reliable solution for quantitative gas temperature sensing. This thesis investigates gas temperature sensing in uniform and non-uniform flows based on LOS absorption of H2O vapor.; The optimized design of tunable diode laser temperature sensors based on H2O vapor absorption first requires a complete catalog of the H2O absorption transitions with accurate spectroscopic parameters. Therefore, extensive experimental studies of H2O spectroscopy were performed over the 1.3-1.5 mum near-infrared region for transitions within the 2nu1, 2nu3, and nu1+nu3 bands. These new spectroscopy measurements provide systematic examination of the sensor design capability of the HITRAN spectroscopy database for combustion and other applications at elevated temperatures. We found HITRAN2004 is sufficiently accurate for sensor design but quantitative sensor calibration requires additional spectroscopic data of better accuracy.; Two-line thermometry provides a simple but efficient solution for LOS absorption gas temperature sensing. This thesis provides two examples. One example is temperature sensing for gas turbine exhaust, which has relatively uniform temperature. A scanned-wavelength direct absorption spectroscopy two-line thermometry was designed and demonstrated for this application. The other example is in-cylinder temperature sensing for the compression stroke of internal-combustion engines, which has limited optical access with a very short sample path. Two-line thermometry based on the fixed-wavelength scheme and wavelength modulation spectroscopy with 2f detection was designed to address the challenges associated with the weak absorption signals and the fast changing temperatures and pressures of this example application.; A novel multi-line thermometry strategy based on H2O vapor absorptions is developed for temperature sensing in non-uniform flows. The sensor concept is to measure the LOS absorptions for multiple H2O, vapor transitions with; different temperature dependences, from which the non-uniform temperature distribution along the LOS can be inferred. The detailed mathematic models were established and the sensor design rules were investigated to generate systematic line selection criteria. Both simulation calculations and laboratory experiments were performed to provide proof-of-concept demonstrations and investigate sensor performance. The extensive theoretical, simulation and experimental studies provide the basis for future applications of multi-line thermometry to practical combustion diagnostics.