Development of a High-Pressure Gaseous Burner for Calibrating Optical Diagnostic Techniques

Source: NTRS


In this work-in-progress report, we show the development of a unique high-pressure burner facility (up to 60 atm) that provides steady, reproducible premixed flames with high precision, while having the capability to use multiple fuel/oxidizer combinations. The highpressure facility has four optical access ports for applying different laser diagnostic techniques and will provide a standard reference flame for the development of a spectroscopic database in high-pressure/temperature conditions. Spontaneous Raman scattering (SRS) was the first diagnostic applied, and was used to successfully probe premixed hydrogen-air flames generated in the facility using a novel multi-jet micro-premixed array burner element. The SRS spectral data include contributions from H2, N2, O2, and H2O and were collected over a wide range of equivalence ratios ranging from 0.16 to 4.9 at an initial pressure of 10-atm via a spatially resolved point SRS measurement with a high-performance optical system. Temperatures in fuel-lean to stoichiometric conditions were determined from the ratio of the Stokes to anti-Stokes scattering of the Q-branch of N2, and those in fuel-rich conditions via the rotational temperature of H2. The SRS derived temperatures using both techniques were consistent and indicated that the flame temperature was approximately 500 K below that predicted by adiabatic equilibrium, indicating a large amount of heat-loss at the measurement zone. The integrated vibrational SRS signals show that SRS provides quantitative number density data in high-pressure H2-air flames.

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    • "This involves the need to acquire a comprehensive set of data in the same facility, including wall heat fluxes along with inflow measurements over a broad range of pressures [2]. The experimental data for CFD validation acquired to date were obtained from a range of facilities of different sizes, various internal geometry or fuel composition, and injection configurations [3] [4] [5] [6] [7] [8] [9]; therefore, wall heat fluxes were considerably different among these studies. The strength, the life cycle, and the cooling system effectiveness are highly dependent on heat transfer into and out of the system [10], and the number of studies addressing the heat transfer into the chamber walls are still inadequate. "

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    ABSTRACT: We present a theoretical study of the spectral interferences in the spontaneous Raman scattering spectra of major combustion products in 30-atm fuel-rich H2–air flames. An effective methodology is introduced to choose an appropriate line-shape model for simulating Raman spectra in high-pressure combustion environments. The Voigt profile with the additive approximation assumption was found to provide a reasonable model of the spectral line shape for the present analysis. The rotational/vibrational Raman spectra of H2, N2, and H2O were calculated using an anharmonic-oscillator model using the latest collisional broadening coefficients. The calculated spectra were validated with data obtained in a 10-atm fuel-rich H2–air flame and showed excellent agreement. Our quantitative spectral analysis for equivalence ratios ranging from 1.5 to 5.0 revealed substantial amounts of spectral cross-talk between the rotational H2 lines and the N2O-/Q-branch; and between the vibrational H2O(0,3) line and the vibrational H2O spectrum. We also address the temperature dependence of the spectral cross-talk and extend our analysis to include a cross-talk compensation technique that removes the interference arising from the H2 Raman spectra onto the N2, or H2O spectra.
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    ABSTRACT: The objectives of experimental research in turbulent, combusting flows are to quantify the extent of fuel-oxidizer mixing, evaluate combustion efficiencies and study finite rate chemistry effects. Optical light scattering techniques such as Rayleigh, Raman scattering and Laser Induced Fluorescence provide non intrusive diagnostics for chemically reacting flows. The experimental setup has to be calibrated at standard conditions to evaluate calibration constants and calibration functions that account for optics and instruments efficiencies. Optical diagnostic techniques depend on the amount of light collected from the probe volume. The intensity of collected light is a function of temperature and number density of molecules in the sample volume. In turbulent flows, the collected light intensity signifies the effect of turbulence which creates heat transfer and random mixing. Hence, calibration has to be performed at laminar flow and adiabatic conditions to evaluate optics and instruments efficiencies with minimum or no effect of turbulence. In pursuit of this goal, this paper describes the design of a calibration burner which produces laminar adiabatic flames. Temperature measurements were made in the post flame zone (chemical equilibrium) of the burner using spontaneous (linear) Raman scattering from fuel lean to fuel rich mixtures. The measurements along with computed uncertainties in temperature were compared with theoretical (adiabatic) flame temperatures. These results including uncertainties are compared with results from other calibration sources to highlight the unique and novel design aspect of this burner. Further improvements in design are suggested to reduce uncertainties in measurements and establish this burner as an ideal calibration source to be used for supersonic and hypersonic reacting flow experiments.
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