Experimental characterization of a liquid-liquid co-axial swirl rocket injector using non-invasive optical and X-ray techniques

Thermo-acoustic combustion instability is a problem that has been researched for decades as it is a precursor to sudden catastrophic failure. Meanwhile, the demand for rocket engines that are able to maintain stable combustion over a wider range of thrust levels is increasing. One injector design utilized in Russia and Asia that has demonstrated stable throttling ability is the liquid-liquid co-axial swirl injector. Simultaneously, interest in alternative hydrocarbon rocket fuels has led to research on a wide range of fuel compositions that deviate from conventional kerosene-based rocket fuel. Hence, it is also necessary to determine how fuel properties will affect the performance of particular injector designs. The goal of the current work is to characterize the atomization and spray properties of a liquid-liquid co-axial swirl injector to evaluate feasibility for potential use in rocket engines. This work was accomplished through the use of non-invasive optical and X-ray techniques including high-speed imaging, phase doppler interferometry, X-ray radiography, and three-dimensional computed tomography. These techniques provided information about break-up mechanisms, break-up lengths, droplet size distributions, and time-averaged liquid mass distributions. An injector with five different nozzle exit geometries was designed, constructed, and implemented for these experiments. The current work was able to demonstrate that geometrical factors such as design of the recessed nozzle exit segments can be optimized to increase breakup and promote more uniform particle distributions. Additionally, the study quantified flow characteristics of the injector over a large number flow parameters, including injection pressure and liquid properties, allowing for better