On development of green storable liquid rocket engine with thrust variation

The Throttleable Liquid Propulsion Demonstrator is a liquid rocket engine demonstrator designed to enable deep throttling using green propellants: High-Test Peroxide at 98% concentration and ethanol at 96% concentration. Throttling is achieved through two independently-actuated cavitating mass flow regulation valves. No additional ignition device is utilized, as the catalytic decomposition of the oxidizer provides sufficient heat to ignite the mixture smoothly. Combustion performance and stability are improved through a variable-geometry fuel pintle injector, while the oxidizer injector remains fixed at this development stage. The technology enables thrust modulation down to 10% and up to 110% of the nominal operating point (5 kN at sea level). A major milestone in the project was the hot-fire test campaign of the engine, which was split in two phases. The first phase focused on static testing without active throttling, to evaluate the engine’s performance envelope and acquire input for control laws for targeted throttling, while the second phase tested dynamic thrust variations, incorporating closed-loop control to ensure operational stability and accuracy. This paper presents the results of the first phase of the engine’s development with emphasis on hot-fire test results, where engine managed to achieve 10% of thrust with high combustion efficiency, encountering efficiency decrease for high thrust region. Thrust up to 100% was demonstrated. Despite of efficiency decrease for the high level of thrust, good agreement between system’s modelling and test was achieved, with proper controller action for combustion pressure stabilization during firings. The technologies developed within the activity are considered potential building blocks for green storable propulsion applications, such as recoverable boosters, planetary or lunar landers, and kick-stages. The TLPD project is part of the Future Launchers Preparatory Programme of the European Space Agency. • There is limited experience regarding green deep-throttleable rocket engines • A new throttleable engine using 98% hydrogen peroxide and 96% ethanol is described • Cavitating venturi valves and a variable geometry pintle injector are used • Deep throttling down to 10% of nominal thrust has been demonstrated • Promising high-efficiency and performance demonstrated for low thrust