Optimization of SLIPI-polarization ratio imaging for droplet sizing characterization of dense sprays

Abstract

Abstract In this paper, the combination of structured illumination method and polarization ratio technique is successfully applied to the particle sizing of an industrial dense water spray. The polarization ratio technique is based on the acquisition of the perpendicular and parallel polarized components of Lorenz-Mie scattered light, which ratio is proportional to the surface mean diameter, D21. One of the main advantages of this technique, compared to some other laser imaging techniques for particle sizing, is that no fluorescent dye is required. This makes the technique suitable for the characterization of sprays under evaporating conditions, such as combustion applications. The aim of this work is to study the experimental parameters that influence the reliability of the technique, such as the orientation of the incident light polarization, the complex refractive index or even the scattering angle. The results show that the intensity oscillations are strongly attenuated when the incident signal is predominantly in parallel polarization. Furthermore, it is shown that the technique is applicable for refractive indices larger than 1.4, by choosing carefully the scattering angle. Additionally, in order to attenuate the strong Mie ripples, which appear in the scattered light intensity, measurements are carried out in a polydisperse spray. Finally, a 3D reconstruction of D21 is performed on a dense industrial spray, using a calibration by the phase Doppler anemometer technique. This quantitative result shows the robustness and efficiency of the technique.