One-dimensional imaging of H2 densities and of temperatures via rotational Raman scattering of narrow-band, 248 nm, laser light

Abstract

It is demonstrated that the well known rotational Raman spectrum of H2 can be used to find the relative densities of hydrogen and the gas temperature as a function of position. A line‐shaped beam from a tunable excimer laser intersects H2–air flames. Scattered light is acquired with an imaging spectrograph. This produces both Stokes and anti‐Stokes spectra. By adjusting the laser beam’s polarization, the interfering Rayleigh intensity is sufficiently reduced without the use of a filter. The temperature measurements can be from below room temperature to about 1200 K. The method also works at temperatures >1200 K, but the use of vibrational Raman spectroscopy is probably better there. Also shown is an image that has simultaneously acquired, spatially resolved spectra from rotational Raman, vibrational Raman and laser‐induced fluorescence. Such combined information might be used to diagnose a gaeous system in some detail. © 1997 John Wiley & Sons, Ltd.

Single-shot rotational Raman thermometry for turbulent flames using a low-resolution bandwidth technique

“…Figure 5 shows a comparison of the measured temperatures using the present ERB method to the temperatures obtained using other (conventional) techniques applied to the same Raman spectra (200-shot on-chip accumulated average). From figure 5, we can see that while the vibrational N 2 SAS method was applicable throughout the equivalence ratios, the rotational H 2 method (line intensity distribution) [22,28] was limited to fuel-rich (hydrogenrich) conditions as H 2 molecules were fully consumed in fuel-lean flames. The present ERB method was limited to hydrogen-lean flames since the rotational H 2 lines interfered significantly with the rotational N 2 spectrum in hydrogenrich conditions.…”

“…Despite the encouraging results, such previous studies with high-resolution spectroscopy often sacrifice temporal resolution, and are not typically performed simultaneously with vibrational spectroscopy due to the limits in spectrograph spectral range at high resolution. The purerotational scattering of hydrogen has also been used for measuring flame temperatures in H 2 -air flames using a ultraviolet laser with a polarization technique [22], although this technique is not as useful for fuel-lean combustion systems with hydrocarbon fuels, where the levels of combustionintermediate-formed hydrogen is often very low. In contrast to these population-distribution-based methods, our technique utilizes a wavelength-or frequency-domain approach that is independent of absolute signal amplitude.…”

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

“…N 2 Raman thermometry using the anti-Stokes/Stokes intensity ratio of the vibrational N 2 Qbranch (AS-S method) [35], or spectrally line-fitting to the shape of the N 2 Q-branch (N 2 line-fit method) [36] are well known. H 2 Raman thermometry [6,37,38] using the line intensity distribution of rot-H 2 is a good alternative in H 2rich flames since rot-H 2 has a relatively strong cross section and each rotational spectrum is discriminated very well due to relatively large rotational level spacing. Intensity-integration calculations can also be effectively implemented to increase the signal-to-noise ratio.…”

“…In particular, spontaneous Raman scattering (SRS) has been a popular method of probing flames because it is one of the few techniques that provides quantitative multi-species, point measurements in turbulent reacting flows [1,2]. Although spontaneous Raman signals are inherently very weak, one can expect high quality SRS data with good signal-to-noise ratio (SNR) using either UV laser excitation [3][4][5][6][7][8] or visible laser excitation in conjunction with a high-performance optical set-up that utilizes a pulse-stretcher, mechanical shutter and high-sensitivity detection methods [9][10][11]. Thus, even single-shot measurements with good SNR can be achieved in turbulent flames using SRS.…”

Spontaneous rotational Raman thermometry for air flow characterization in a turbomachine test rig

“…The accuracy of SR2S technique was shown to be very good at ambient temperature. For example, Drake et al have mentioned an accuracy of ±2 K at about 300 K using signal accumulation over 45 s and ~2.2% in single shot by Locke et al In the past, among various applications, SR2S has been used for temperature measurements in flames and in the atmosphere . In particular, this technique was applied to thermometry in a high‐velocity turbulent jet, in a gas turbine model combustor at elevated pressure, in a confined swirling natural gas/air flame, in high‐pressure fuel‐rich H 2 ‐air flames, and in the UV range for imaging of a JetA‐fueled aircraft combustor.…”