Development of an Optically Accessible Green Hypergolic Rocket Engine with Bi Swirl Injector

This work aims to investigate the flow and ignition dynamics of hypergolic propellants by designing, fabricating, and testing a bipropellant thruster that incorporates direct optical access throughout the entire system. Unlike conventional thrusters, the presented design integrates a transparent chamber, injector, and fluid components, enabling unobstructed visualization of the complex phenomena occurring during propellant injection, mixing, and combustion. Optical access provides a unique diagnostic capability, allowing researchers to employ high-speed imaging, laser-based techniques, and spectroscopy to capture transient ignition events, flame structure evolution, and flow-field interactions. These insights are critical for advancing the fundamental understanding of hypergolic ignition chemistry and fluid dynamics, ultimately informing the development of safer, more reliable, and more efficient propulsion systems. The thruster is engineered to meet stringent performance requirements, delivering up to 25 lbf of thrust over a minimum one-second firing duration, and features a perfectly expanded nozzle for atmospheric operation. The propellant combination consists of a triglyme and 8 wt.% sodium borohydride fuel solution paired with 90 wt.% hydrogen peroxide oxidizer, selected for its hypergolic behavior and relevance to green propulsion initiatives. By enabling direct visualization of internal processes, the presented approach bridges the gap between theoretical modeling and experimental validation, offering a powerful platform for diagnosing flow instabilities, ignition delays, and combustion efficiency. Such capabilities could not only accelerate design optimization but also enhance safety margins for future space missions and in-space maneuvering systems.