Measurement of Droplet Size, Velocity and Spatial Distribution of Mass Flux in Spray by Combining Focus and Defocus Imaging Technique

Abstract

The novel imaging technique combining Glare-Points technique (GPT) with interferometric laser imaging for droplet sizing (ILIDS) has been developed to measure droplet size, velocity and spatial distribution of mass flux in a spray. This technique enables to advance the droplet positioning error by ILIDS and expand the dynamic range of droplet sizing, because the large and small sized droplets were obtained by using GPT and ILIDS, respectively. The novel receiving optical system called as Double-planes Particle Imaging (DPI) was constructed in order to capture the focus plane (Glare-Points) and the defocus plane (interferometric fringe) with only one imaging sensor. Firstly, the captured image is processed for calculating of the droplet position, size and velocity by GPT and ILIDS, respectively. The droplet position by ILIDS is corrected by the mapping function which is obtained from the ray tracing simulation. Secondly, the same droplet image is matched with the aid of velocity information. In addition, the droplet position is defined as the one of GPT, the droplet size is employed the ILIDS' for smaller and the GPT's for larger than threshold value. Finally, the depthwise positions of droplet are estimated from the optical path difference between the focus and defocus images. From the result of validation experiment using a mono-disperse generator, the DPI enables to estimate the three-dimensional droplet position within the measurement error of 8.4% and expand the dynamic range of the accurate droplet sizing up to approximately 200 μm. Furthermore, this developed technique was applied to a spray flow, and the spatial distribution of mass flux was evaluated from the obtained droplet position, size and velocity information.