| Measurements of water vapor are relevant to combustion, since water vapor concentration can be related to performance parameters such as combustion and propulsion efficiencies, and heat release. The development of a diode-laser based diagnostic to monitor water vapor and temperature in high-pressure and -temperature environments relevant to combustion by probing near-IR H 2O absorption features near 7117 and 7185 cm−1 is described.; A comprehensive review of line-shape modeling that highlights spectroscopic phenomena that become important at high pressures, such as the breakdown of the impact approximation in the wings and line mixing due to inelastic collisions, is presented. A decision tree and a road map to choose an appropriate line-shape model are introduced. Spectrally resolved measurements of H2O transitions near 7117 and 7185 cm−1 were performed at sub-atmospheric pressures and over a temperature range of 296–1000 K. Line-shape analyses of the recorded spectra yielded the temperature-dependent self-, N2-, CO2- and Ar broadened half-widths. The room-temperature (296K) half-widths and temperature exponents were determined to an average uncertainty of ±7% and ±9%, respectively.; Good agreement was obtained between static-cell data recorded near 7117 cm−1 and simulations, based on measured line parameters and simple addition of Voigt line shapes, leading to the conclusions that: (1) effects due to line mixing are negligible for number densities up to at least 18 amagat, and (2) line shapes based on the impact and the additive approximations can be used in the development of spectroscopic diagnostics to monitor H2O in high-pressure combustion gases. Super-Lorentzian behavior was observed near 7185 cm−1 and is attributed to finite duration of collision effects neglected by impact line shapes. Water-vapor absorption features near 7117, 7185 and 7462 cm−1 were probed at pressures and temperatures to 65 atm. and 1800 K, in shock-heated mixtures of H2O in N2 and Ar. Temperature-dependent N2- and Ar-shift parameters for H2O absorption features were obtained by shifting the calculated spectra to match the recorded absorption data. The measured absorbance at the probed wavelengths was used to ascertain the accuracy of simulations based on current spectroscopic databases. The design of a sensor using diode lasers fixed at 7185.4 and 7117.4 cm −1 to monitor water vapor and temperature in high-pressure combustion gases is discussed. |
