2D-Mapping of the Droplets Sauter Mean Diameter in a Hollow-cone Spray Using SLIPI-LIF/MIE

Abstract:
In this work, we report an original experimental approach for mapping the droplets Sauter Mean Diameter (SMD) of a hollow-cone water spray using the SLIPI-LIF/MIE technique. Water mixed with a non-toxic fluorescing dye is continuously injected at 20 bars injection pressure and the formed hollow-cone spray is illuminated using a continuous wave laser. The illumination wavelength is carefully chosen (here, 447 nm) to excite the injected dye/water mixture, which generates a significant Laser Induced Fluorescence (LIF) signal peaking at 514 nm. The LIF and Mie signals are recorded using a CCD camera and their intensity ratio is used to extract a two-dimensional distribution of the droplets SMD. In this article, we show that even for the case of a dilute hollow-cone spray, where single scattering events are in majority (OD~1), the LIF/Mie measurement of droplets SMD still remains strongly affected by multiple light scattering. We demonstrate, then, that the use of SLIPI is of fundamental importance to obtain trustable SMD measurements based on the LIF/Mie ratio, even for optically dilute sprays.