Validation of laser‐induced thermal acoustics for chemically reacting H₂/air free jets

Abstract

The scramjet engine is a promising propulsion concept for future space transportation systems. To enhance the engine efficiency, a strong understanding of combustion mechanisms is essential. Laser‐induced thermal acoustics (LITA) – a seedless, non‐intrusive measurement technique – is an auspicious technique for the investigation of supersonic combustion. Here, we present two validation cases and first LITA measurements in a chemically reacting hydrogen/air free jet. The first validation case is the investigation of premixed methane/air and hydrogen/air flames, produced with a commercially available flat flame burner. The comparison with coherent anti‐Stokes Raman spectroscopy measurements resulted in a deviation between the two measurement techniques smaller than the uncertainty of the techniques. The second validation case is the investigation of hot, supersonic air/air free jets at total temperatures of Tt = 1050 K and Tt = 1300 K. The comparison with computational fluid dynamics predictions shows a reasonable agreement with a maximum deviation of 13.9% for the free jet with a temperature of Tt = 1300 K and a good agreement with a maximum deviation of 4.4% for the free jet with a temperature of Tt = 1050 K. The LITA measurements in a chemically reacting hydrogen/air free jet showed a good reproduction of the flame position determined from an OH∗ image. For the presented investigations, we used a homodyne, resonant LITA setup with a pulsed interrogation beam. Copyright © 2016 John Wiley & Sons, Ltd.

Remote-sensing gas measurements with coherent Rayleigh-Brillouin scattering

“…To date, the main efforts to provide such a pressure measurement tool have concentrated on the application of laserinduced thermal-acoustics (LITA) and laser-induced thermal grating spectroscopy (LITGS). [14][15][16][17][18][19] Although these methods have successfully demonstrated their applicability in pressure and temperature measurement, they do have some limitations. More specifically, because they are dependent on the laser radiation absorption and subsequent acoustic wave generation, they work well at high pressures (typically above 2 atm) while only one such method has demonstrated its applicability at a pressure below 100 Torr.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Hell and co‐workers carried out a study of the validation of laser‐induced thermal acoustics (LITA) for chemically reacting H2/air free jets. They presented two validation cases and first LITA measurements in a chemically reacting hydrogen/air free jet . Hu et al used a spatial heterodyne spectrometer for the Raman spectroscopic detection of liquid and solid targets.…”

“…They presented two validation cases and first LITA measurements in a chemically reacting hydrogen/air free jet. [184] Hu et al used a spatial heterodyne spectrometer for the Raman spectroscopic detection of liquid and solid targets. Spatial heterodyne Raman spectroscopy (SHRS) is a new type of effective method for the analysis of structure and composition of liquid and solid targets with the characteristics of no moving parts, high spectral resolution, high optical throughput, and large field of view.…”

Advanced Laser-Based Techniques for Gas-Phase Diagnostics in Combustion and Aerospace Engineering

“…Fourkas et al employed two picosecond lasers to resonantly pump and probe sodium atoms seeded into hydrogen and methane flames. 181 Hell et al 182 utilized the absorption band of water around 1 mm to obtain laserinduced thermal gratings in a H 2 /air flame. Methane/air flames were studied by Hart et al, 183 Hemmerling et al, 184 and Stampanoni-Panariello et al 185 All these works employed pump laser sources in the UV, visible, or near-infrared (NIR) spectral range.…”