ABSTRACT
Water-vapor absorption features near 7117, 7185, and 7462 cm(-1) were probed at pressures to 65 atm (1 atm = 760 Torr) and temperatures to 1800 K in shock-heated mixtures of H(2)O in N(2) and Ar with a diode-laser source. Calculated absorbances based on Voigt line shapes and measured line parameters were in good agreement, within 10%, with measured absorbances at 7185.4 and 7117.4 cm(-1). We obtained temperature-dependent N(2) and Ar shift parameters for H(2)O absorption features by shifting the calculated spectra to match the recorded absorption scan. Absorbance simulations based on line parameters from HITRAN and HITEMP were found to be similar over the range of temperatures 600-1800 K and were within 25% of the measurements. The combined use of Toth's [Appl. Opt. 36, 4851 (1994)] line positions and strengths and HITRAN broadening parameters resulted in calculated absorption coefficients that were within 15% of the measurements at all three probed wavelengths.
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 H(2)O 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.
ABSTRACT
A diode-laser sensor system based on absorption spectroscopy techniques has been developed to monitor CH(4) nonintrusively in high-temperature environments. Fundamental spectroscopic parameters, including the line strengths of the transitions in the R(6) manifold of the 2ν(3) band near 1.646 µm, havebeen determined from high-resolution absorption measurements in a heated static cell. In addition, acorrected expression for the CH(4) partition function has been validated experimentally over thetemperature range from 400 to 915 K. Potential applications of the diode-laser sensor system includeprocess control, combustion measurements, and atmospheric monitoring.
