Simultaneous droplet and vapour-phase measurements in an evaporative spray by combined ILIDS and PLIF techniques

This paper presents a novel optical technique for simultaneous planar measurement of droplet and vapour phases in an evaporative spray. The technique combines the out-of-focus imaging technique 'Interferometric Laser Imaging for Droplet Sizing' (ILIDS) for planar simultaneous measurements of droplet size, velocity, and number density with the in-focus technique 'planar laser-induced fluorescence' (PLIF) for measurements of vapour concentration around individual droplets. As with the combined ILIDS and PIV technique (Hardalupas et al. in Exp Fluids 49:417-434, 2010), a discrepancy occurs in the location of the same droplet while imaging through both techniques. The centre discrepancy is experimentally estimated, and so, the position of the droplet centres in the ILIDS image can be corrected, which is essential for the measurement of the correlation of the local vapour concentration with its corresponding droplet size and velocity. The combined technique is first applied to mono-sized acetone droplet stream for two droplet sizes, which have different inter-droplet distances. A new method is proposed for the correction of the 'halation' effect around droplets on vapour fluorescence intensity around the mono-sized droplets in the PLIF image. A phase discrimination method to separate droplet and vapour fluorescence in PLIF images of evaporative sprays is explained. It is shown that the combined ILIDS and PLIF technique is an effective tool for studying group evaporation of droplets and interaction between the two phases in an evaporative spray © Springer-Verlag Berlin Heidelberg 2014.