Year: 2025
Type: conference-paper
Abstract: This paper aims to provide a detailed report of the various processes used to design, hot fire, and analyze Serenity, the Buckeye Space Launch Initiative (BSLI)'s first liquid rocket engine. It uses a propellant combination of kerosene and liquid oxygen. Testing shows that it is capable of producing approximately 500lbs of thrust with a specific impulse of 210s. The engine validated various new technologies for the club, as well as allowed us to gain valuable experience while laying a solid foundation for our next engine. The engine was designed to leverage the school's additive manufacturing capabilities. As a result, several geometrically complicated but higher performance design techniques were implemented. The engine uses a monolithic design that is fully additively manufactured. It has a fully regeneratively-cooled nozzle and a 17-unit internal mixing coaxial swirl injector plate to maximize the engine's lifespan, reusability and combustion efficiency while also lowering the overall chamber length. The engine used several advanced Design for Additive Manufacturing (DFAM) techniques and eliminated any overhangs over 45 degrees, which allowed the team to completely manufacture the engine in one print with only minor post processing. The engine was made using NASA’s GRCop-42 alloy which provided the engine with excellent thermal conductivity. This allowed the team to utilize regenerative cooling as the only method of chamber and nozzle temperature management eliminating the performance reduction caused by film and ablative cooling methods. The monolithic design also eliminated any need for inter-component seals enhancing manufacturing speed and reliability. However, later operation of the engine shows a critical lack of maintainability as the engine does not have any means to disassemble. The team’s next engine design, Prometheus, will not be monolithic. A simple e-match solid motor ignition system was used to ensure reliability during ignition, but had a failure rate of approximately 50%. Finally, due to print volume limitations the engine was forced to use a low characteristic length chamber which, during testing, showed signs of combustion instability as the chamber pressure decrease due to the nature of the blow-down system. This issue is addressed on the next engine by printing on a bigger printer and the usage of a pump-fed system which allows the engine to operate under a same chamber pressure throughout the entire burn. The GSE system used in the hot fire test was also the first system that the club had designed. It uses two blow-down tanks to pressurize the system, with each tank pressurized by their own nitrogen tank. The propellant mass in both tanks were directly measured by load cells. Any sideway forces were cancelled out by a linear rail system. The test stand mainly uses pneumatic valves to ensure actuation and reactiveness under cryogenic conditions. These valves are powered by small solenoid pilot valves. The actuation of the valves were directly controlled using a manual control box. Extensive FEA was performed to ensure the structure was sound during engine firing. The team also laid down a concrete pad to ensure stability of the ground and anchorage of the stand during firing while maintaining accuracy on the load cells. The electronic system mainly consisted of data acquisition and system control. The data acquisition system is based on a LabJack which monitors all vital data, and feeds it over ethernet to laptop. The laptop runs a custom Python script to graph and calibrate the sensors. This data is used for control, operation and analysis of the engine’s performance. The control system consists of a control box directly linked to our test stand, which allows the team to remotely control the valves at a safe distance and operate the test stand. Overall, three fire attempts were conducted and two successful fires were accomplished. The engine fired for 5 and 10 seconds in quick succession, and all systems functioned nominally during the fire. No damage to the engine or surrounding equipment was seen. The engine is currently intact; no signs of overheating was seen on the chamber and nozzle, validating the regenerative cooling system design. A significant combustion instability was seen towards the last half of the burn as the chamber pressure degrades. The frequencies have been extracted and analyzed, and the issue is addressed in future designs. The injector saw some back flow of hot gas due to the combustion instability as soot was found in the feed manifold of the injector plate. Otherwise, the performance met the expectations, and the injector design is passed to the next engine with various improvements.
Language: English
Subfield: Aerospace Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W4413191086