Consolidating soot optical diagnostics in laminar coflow axisymmetrical flames
Résumé
The detailed study of soot particle formation in academic flames (laminar, stationary) is still necessary to improve the kinetic models of soot particle formation. The information is more accessible and parametric studies are possible (effect of ventilation, fuel, pressure...). The optical techniques allowing the extraction of information concerning soot particles are numerous and rely on different mechanisms. Among these techniques, light extinction, scattering and laser induced incandescence are the most used. The collected signals are interpreted in terms of volume fraction and size by using light-particle interaction models such as RDG-FA. The results thus obtained can suffer from the inaccuracy or the unsuitability of these models and work is to be carried out in this direction. However, the results can also suffer from strong assumptions (for example the complex index of soot considered uniform) or from experimental constraints that can limit, for example, the spatial resolution.
In this presentation, we present two recent advances in optical diagnostics that have been developed and applied to a laminar diffusion flame (Gülder burner fed with ethylene). The first one consists in exploiting the spectral dependence of the attenuation imaging (Line Of Sight Attenuation) in order to remove the uncertainty of the optical index variation driven by the evolution of its maturity. The second one consists in proposing an original experimental configuration of angular scattering (Horizontal Planar Angular Light Scattering) in order to access size information with an improved spatial resolution. Finally, we show the benefit of coupling these two techniques in order to access all the following quantities: temperature, volume fraction, maturity, absorption function, numerical concentration of particles, diameter of primary spherules.