We have recorded laser-induced grating signals from mixtures of NO2 and air over a pressure range extending from less that 100 kPa (1 atm) to 10 MPa (100 atm). Signals generated from concentrations of NO2 at the part-per-million level have been successfully detected with high signal-to-noise rations. The measurements were made using the technique of laser-induced thermal acoustics (LITA). Analysis of the acquired data was made using a comprehensive theory which includes the hydrodynamic response of the fluid and finite beam-size effects. The observed pressure dependence of the peak amplitude signals is consistent with the theory. Additionally, least squares fits between the theory and the temporally resolved signal yield accurate values of the local sound speed and thermal diffusivity. Determination of the local sound speed provides a measurement of the local temperature.
High-temperature water vapor imaging based on Raman scattering for hypersonic exhaust diagnostics has been developed. A temperature-independent UV Raman line imaging instrument that is calibrated with room air and readily scaled to large combustion facilities has been tested in a laboratory H2/air combustor. The H2O concentration measurements exhibit a single-shot standard deviation of approximately 8%. In this paper we investigate practical issues concerning the application of UV Raman line imaging for quantitative water vapor measurements.
High temperature water vapor detection in hypersonic exhaust has been the subject of ongoing research in a collaboration between MetroLaser and Vanderbilt University's Department of Mechanical Engineering. In this paper we examine some of the temperature sensitivity issues surrounding water vapor diagnostics based on two-photon fluorescence measurements. We present work which shows a large temperature sensitivity for the two-photon excited fluorescence features for H2O in a hydrogen and air flat flame burner. The spectra are modeled for various temperatures, results are experimentally verified, and recommendations are made.
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