ILASS-Americas 29th Annual Conference on Liquid Atomization and Spray Systems, Atlanta, GA, May 2017 The Effect of Doublet Injector Orifice Geometry on Spray Characteristics S. B. Leask and V. G. McDonell * UCI Combustion Laboratory University of California, Irvine Irvine, CA 92697 USA Abstract Doublet injectors have been studied parametrically in past work focusing on, for example, orifice length to diameter ratio, impingement angle, and injection velocity. The effect of orifice geometry has been comparatively under-studied although it has a significant impact on the impinging jet stream dynamics. Few works have been presented since the inception of orifice geometry studies for doublet injectors, yet the findings on the effectiveness of non-circular orifices have been acknowledged since the 1970’s. Of particular promise is the use of rectangular orifices. Many initial draw- backs of non-circular orifices have since been remedied, for example, the precise design and manufacture of the orifice shapes. Yet little work has been done recently to affirm the benefits of rectangular geometries. As a result, the present study examines the effect of changing orifice geometry of doublet injectors on the resulting spray characteristics. Circular geometries are compared to rectangular orifices of varying aspect ratio. The effect of the orifice geometries on Sauter mean diameter, span, fuel and oxidizer mixing, and spray velocity vector fields are characterized for various test conditions. Injection velocity and impingement angle were varied to provide results for different cases. Data were collected at four downstream locations using multiple laser diagnostic systems to provide spray-averaged results. The results indicate affirms that improved mixing efficiency can be achieved through using rectangular orifices over cir- cular orifices. Finer atomization can also be produced through the use of rectangular orifices, but greater droplet size non-uniformities can be present. The rectangular jet streams show greater stream instability compared to circular jet streams, possibly due to the axis-switching phenomenon, which can lead to increased mis-impingement for rectangular orifices depending on the conditions and impingement distance. * Corresponding author: mcdonell@apep.uci.edu