Comparison of like on like doublet and triplet impinging jet injectors

A comparison of three types of like-on-like impinging jet injectors under ambient conditions is conducted. The three atomizers are a doublet, a linear triplet and a 3D (or circular) triplet injector. The spray characterization is carried out with a Malvern Spraytech, an instrument based on laser diffraction, for measuring the spray droplets size and with the shadowgraph technique which allows the visualization of the spray shape and patterns. The tests on the three injectors are performed with four Newtonian liquids: water, ethanol, 30% and 87% glycerine -water mixtures so that the physical properties (density, cinematic viscosity, surface tension) of the tested liquids can be varied in a broad range. The range of injection velocities is between 10 and 60 m/s. The Sauter Mean Diameter of the spray centerline, the difference of the SMD between the spray centerline and the spray edges and the droplets concentration into the spray are measured with the Malvern Spraytech, while the cone angles are determined from the shadowgraph images. The results are presented as function of the injection velocity and feeding pressure. The most significant result of the present work is that the triplet injectors produce larger droplets than doublet; in particular the 3D triplet develops larger droplets than the linear triplet and the doublet injectors, but it allows for a conical shape spray, more uniform and homogeneous.