Abstract

The design of a diode-laser sensor to monitor water vapor in high-pressure combustion gases is described. The sensor, which employs a multiple-fixed-wavelength absorption strategy, has the potential to simultaneously monitor the water mole fraction and the temperature and pressure in high-pressure and high-temperature environments. The conventional scanned-wavelength strategy, employed in previous diode-laser sensors, is shown to be ill-suited for high-pressure applications. The application of impact and additive approximations in the modeling of H₂O absorption features at high pressures is validated experimentally for number densities as high as 18 amagats. Criteria to select optimum wavelength combinations for the fixed-wavelengths strategy are discussed. Optimum wavelength combinations that meet these criteria are identified for different temperature and pressure ranges of interest to combustion applications. The proposed sensor configuration and a strategy to obtain the baseline (zero absorption intensity) in high-pressure environments are also described. Line-shape models that are appropriate for different temperature and pressure regimes are identified.

© 1997 Optical Society of America

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