LUMEN: Putting into Operation a Flexible Test Bed for Next-Generation Rocket Engine Technologies

Abstract

In 2024, the German Aerospace Centre (DLR) successfully completed the hot-fire testing of the Liquid Upper Stage Demonstrator Engine (LUMEN), marking the final milestone in developing DLR's first rocket engine. LUMEN is an experimental expander-bleed cycle rocket engine that uses liquid oxygen (LOX) and liquefied natural gas (LNG) as propellants, generating 25 kN of thrust. With this achievement, LUMEN is now fully operational and available as a test bed for advanced technology development, such as intelligent engine control. LUMEN’s open research platform, free from external intellectual property restrictions, enables DLR to offer it as a testing platform to interested partners both domestically and internationally. Its modular design allows for component evaluations in a realistic environment, and the engine as a whole can support the development of engine-related technologies that would otherwise be challenging to test. After the initial tests of LUMEN, a subsequent test campaign was conducted with a focus on operating the engine as a research test bed. LUMEN was also used to demonstrate the intelligent control with a neural network controller. To establish a baseline design for the next step in intelligent control, some improvements are implemented. A new LOX impeller in the Oxygen Turbopump (OTP) provides a higher efficiency, while the cycle is optimized by reducing pressure losses throughout the system by removing two valves and introducing a newly optimized injector head. The new injector head uses shear coaxial elements in the outer row and swirl elements in the inner row, which not only reduce pressure losses but also enhance flame anchoring and heat transfer. Furthermore, the chilldown time was shortened to reduce the amount of propellant necessary for engine cooling while simultaneously deepening the understanding of chilldown prediction. Both, the operation time and the overall system efficiency were significantly improved during this campaign. The results of these tests will be presented in this paper.