Heidelberg 1999 – scientific programme
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Q: Quantenoptik
Q 26: Poster: Laserspektroskopie
Q 26.9: Poster
Tuesday, March 16, 1999, 16:30–18:30, PH
Laser spectroscopy in sooty flames: Polarisation spectroscopy versus laser-induced fluorescence — •J. Walewski1, A. Dreizler2, K. Nyholm3,1, and M. Aldén1 — 1Lund Institue of Technology — 2Universität Stuttgart — 3Helsinki University of Technology
The presence of soot in combustion processes leads to intense scattering of laser radiation when detecting flame species with laser spectroscopic methods. This may induce a significant background radiation on the signal from the excited species, which can make it impossible to interpret the signal quantitatively. Coherent techniques offer the possibility of filtering the emitted radiation spatially without any significant loss to the signal from theexcited species. Therefore there should be a high potential of using coherent laser-spectroscopic techniques for the diagnostic in sooty flames. In this work the signals from polarisation spectroscopy (PS) and LIF in partial premixed and diffusion flames for a propane/oxygen mixture are compared. For different fuel to oxygen ratios, φ, and different heights over the burner head, PS and LIF signals from OH radicals were recorded for sooty and non-sooty conditions. The measurements show a much lower sensitivity of the PS signals to non-resonant scattering of the soot particles. The origin of the faint scattering signal in PS is identified as Rayleigh scattering of the intense pump beam. It is demonstrated how spatial filtering can be used to suppress the background radiation by orders of magnitude.