Droplet size and concentration mapping in sprays using SLIPI based techniques

Abstract:
Laser diagnostics have become state of the art tools for locally measuring droplet size, velocity and temperature in atomizing sprays. However, when applied in optically dense situations, these techniques suffer from measurement errors induced by unwanted effects such as laser intensity reduction along the path of propagation (light extinction), attenuation in signal intensity collected by the detector (signal attenuation) and multiple light scattering emerging from non-illuminated sections. It has been recently demonstrated that such issues can be addressed by means of imaging techniques based on structured illumination. Therefore, in this article, Structured Laser Illumination Planar Imaging (SLIPI) is applied in combination with the LIF/Mie ratio method and with the dual configuration (Dual-SLIPI) to extract a reliable 2D map of the Sauter Mean Diameter (SMD) and of the extinction coefficient (µe), respectively. This has been applied for the characterization of a hollow-cone water spray at injection pressures ranging between 20 and 50 bars. The SLIPI-LIF/Mie ratio is calibrated with measurement data from Phase-Doppler Interferometry (PDI). Furthermore, the measured droplet size distributions have been used to deduce the corresponding averaged droplet extinction cross-section (σe) using the Lorenz-Mie theory. Consequently, by dividing the 2D images of µe by σe a mapping of the droplet concentration could also be obtained. The changes of droplets size and concentration as a function of injection pressure are shown in this article