Since 2008, Institute of Aeronautics and Space (IAE) has made efforts into L75 Liquid Rocket Engine and a cooperation agreement was signed in 2011 with the Deutsches Zentrum für Luft—und Raumfahrt, the German Aerospace Center (DLR), aiming the L75 engine development. The achievement of adequate combustion stability was a major task, since the beginning. A novel methodology in stability studies regarding combustion stability of Lox/Ethanol propellant combination is proposed in this work. Basic studies and design investigations were performed, adopting a stability assessment strategy in two phases: First phase: L75 combustion chamber acoustics (frequencies and mode shapes) were obtained at room and hot temperatures by theoretical/experimental approaches. Second phase: two hot test campaigns were conducted at P8 test facility-DLR, with 21 hot tests. In 7 run-in tests, a Stainless Steel Capacitive cooled Thrust Chamber (SCTC) was used allowing burning up to 2 s. Instability phenomena were observed during pressure build up. Afterward, 14 tests were performed using Copper Cooled Thrust Chamber (CCTC) and no instability phenomena were observed, even at lower mass-flow then expected in test envelop (load point E6*) combined with low O/F ratios. CCTC allowed longer burning, increased up to 6 s. It is important to highlight that the burning times were calculated by using heat flux estimations at the SCTC/CCTC chamber throats to avoid damages in this critical region by steel/cooper melting. As the CCTC has better heat conductivity, longer burning times were established for this chamber. The measured data showed good agreement regarding the natural frequencies (and respective mode shapes), estimated in the first phase, indicating that the acoustic dynamics of the chamber was appropriately characterized.
