Visual characterization of atomization in additively manufactured impingement injectors

A digital image processing technique was newly developed by integrating multiple processing routines to analyze and evaluate the impingement and atomization performance of like-on-like, additively manufactured liquid bipropellant injectors for thruster applications. This study represents the first systematic evaluation of atomization characteristics in additively manufactured impinging jet injectors. Injector samples were fabricated from Inconel 718 using two different additive manufacturing systems. Water was employed as a substitute propellant to simulate atomization, and experiments were conducted at three injection pressure levels. Shadowgraph images were captured using a high-speed camera with a custom telecentric optical setup and processed with algorithms developed within the program, enabling quantitative characterization of impinging jet angles, droplet size and distribution, and ligament formation and morphology. The results revealed that differences between the additive manufacturing systems affected both the flow resistance within the orifice and the accuracy of jet impingement. Scanning electron microscopy analysis showed that these effects arose from variations in orifice diameter and surface finish. While atomization performance was also influenced, it was primarily governed by jet momentum. The findings demonstrate the capability of the developed image processing algorithm to comprehensively evaluate additively manufactured injector performance. The results provide critical insights into the influence of additive manufacturing on flow behavior and atomization, offering guidance for the design and development of cost-effective thruster injectors with optimized performance.