Three-dimensional mass fraction distribution of a spray measured by X-ray computed tomography

In order to design a spraying system with the desired characteristics, the atomization process has to be understood in detail, including the primary break-up oj the liquid core. Accurate prediction of primary break-up is a major barrier to computer-based analysis of spray combustion. The development of models is hindered by the lack of validation data in a region where the fluid is dense, and optical access is therefore limited. The present experimental study is aimed at probing the spray structure by means of X-ray computed tomography (CT). A full-cone atomizer (0.79 mm orifice diameter) spraying in air at ambient pressure is investigated as a proof of concept. A mixture of water and iodine is used as the working fluid, providing elevated X-ray absorption and therefore improved signal-to-noise ratio. Several hundreds of X-ray projections are acquired as the spraying atomizer is rotated in front of the detector. Standard software for medical imaging is used to reconstruct the three-dimensional time-averaged distribution of liquid mass fraction in the full field of view, from the intact liquid core to the dilute spray region. A spatial resolution of 0.6 mm is obtained along the spraying direction, while the resolution is 0.3 mm in the other two directions. Significant asymmetries in the structure of the spray are revealed.