V. Nagali

Tunable diode-laser absorption measurements of methane at elevated temperatures

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.

Design of a diode-laser sensor to monitor water vapor in high-pressure combustion gases.

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.

Diode-laser measurements of temperature-dependent half-widths of H2O transitions in the 1.4 μm region

Abstract Two distributed-feedback InGaAsP diode lasers have been used to perform spectrally resolved measurements of H2O transitions near 1.4 μm. Line-shape analyses of the recorded absorption spectra yielded the temperature-dependent self-, N2-, and CO2-broadened half-widths. Room-temperature (296 K) half-widths for eight rovibrational transitions in the v1 + v3 and 2v1 vibrational bands were determined from measurements recorded in a variable pathlength (0.4–10 m) multi-pass cell. The temperature dependence of the half-widths for four of the transitions were determined from measurements conducted in a heated static cell over a temperature range of 400–1000 K. The room-temperature half-widths and temperature exponents were determined to an average accuracy of +8% − 6% and ± 9% , respectively, and are in good agreement with theoretical calculations and published half-widths for transitions with the same rotational quantum numbers.

Shock-tube study of high-pressure H 2 O spectroscopy

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 H2O in N2 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 N2 and Ar shift parameters for H2O 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.

Measurements of temperature-dependent argon-broadened half-widths of H2O transitions in the 7117 cm−1 region

Abstract A distributed-feedback InGaAsP diode laser has been used to perform spectrally resolved measurements of H2O transitions near 7117cm−1. Line shape analyses of the recorded absorption spectra yielded the temperature-dependent Ar-broadened half-widths. Room-temperature (296K) half-widths for four transitions were determined with an uncertainty of +7%/−5%. Temperature exponents for three of these transitions were determined over the range of 296–473 K with an uncertainty of ±7%.