Measurement and simulation of spontaneous Raman scattering in high-pressure fuel-rich H₂–air flames

Abstract

Rotational and vibrational spontaneous Raman scattering (SRS) spectra of H 2 , N 2 and H 2 O have been measured in H 2 -air flames at pressures up to 30.4 bar as a first step towards establishing a comprehensive Raman spectral database for temperatures and species in high-pressure combustion. We have obtained an initial set of measurements that indicate the spectra are of sufficient quality in terms of spectral resolution, wavelength coverage and signal-to-noise ratio for use in the development of transferable standards for the cross-talk calibration matrix. The fully resolved Stokes and anti-Stokes shifted spectra were collected in the visible wavelength range (400-700 nm) using pulse-stretched 532 nm excitation and a spectrograph fitted with a non-intensified CCD detector and a high-speed shutter. Temperatures were determined via the intensity distribution of rotational H 2 lines at stoichiometric and fuel-rich conditions. A discussion of the temperature measurement accuracy in terms of the number of laser shots, including a single-shot measurement, is presented. Theoretical Raman spectra of hydrogen were calculated using a semi-classical anharmonic-oscillator model with recent pressure broadening data and were compared with experimental data. The data and simulation showed good agreement at different equivalence ratios and pressures and indicate that high-J rotational lines of H 2 may interfere with the N 2 vibrational Q-branch lines, which could lead to errors in N 2 -Raman thermometry based on the line-fitting method. In addition, the relative intensities of the O-and S-branches to the Q-branch were determined theoretically and the result indicates that further studies of spectral interferences including contributions from O-and S-branches should be pursued. Finally, from a comparison of N 2 Q-branch spectra in lean H 2 -air flames at nearly atmospheric (1.2 bar) and high pressure (30.4 bar), we found no significant line-narrowing or -broadening effects at a spectral resolution of 0.04 nm.

Concentration‐Dependent Hydrogen‐Bonding Effects on the Dimethyl Sulfoxide Vibrational Structure in the Presence of Water, Methanol, and Ethanol

“…It is nowadays a well-established method in both engineering (e.g. for the measurement of temperature [27,28] and concentration [29][30][31] ) and science (e.g. for the analysis of molecular structure).…”

PIV, 2D-LIF and 1D-Raman measurements of flow field, composition and temperature in premixed gas turbine flames

“…In some research groups, high-pressure test rigs have been equipped with optical access in order to apply these techniques to GT combustion processes under realistic conditions, i.e. preheated air, high thermal loads, high turbulence levels and relevant combustor geometries, see for example [15][16][17][18][19][20][21][22][23][24].…”

Miniaturized Combustor for Supersonic Methane–Air Flames

“…The presence of windows would be detrimental to a low signal scattering technique, such as the incoherent Raman scattering that we employ [12]. Despite that, incoherent Raman techniques have been used in isobaric environments using windows [13,14]. Optically accessible supersonic flames have been developed in the past that do not hinder techniques such as incoherent Raman [15,16].…”