International audienceThe aim of this work is to study the role of the liquid phase in the thermo-acoustic coupling which subsequently leads to combustion instabilities. Experimental investigations were performed on an actual multipoint spray injector geometry used in real aeronautical combustors. A test bench was specifically designed with continuously changeable acoustics conditions; which allows obtaining a stable or an unstable flame for identical flow conditions. Different laser-based visualization techniques were used to analyze the kerosene spray (both liquid and vapor phases) and the heat released from the flame. A phase-averaged data processing of the Planar Laser-Induced Fluorescence (PLIF) images reveals the complex unsteady behavior of the liquid phase and its coupling with pressure fluctuations in the chamber and the heat released from the flame. The origins of the spray fluctuations are also analyzed. Nomenclature = surface of the control system boundary, m 2 = volume of the control system, m 3 = heat capacity ratio = characteristic time, s dA = surface integration variable, 1 m 2 dt = time integration variable, 1 s dV = volume integration variable, 1 m 3 D REF = reference diameter F = Flame Describing Function FSP = Fuel Split Parameter GER = Global Equivalent Ratio I = light intensity over camera dynamics, # counts IEL = Inner Exhaust Length, mm J = momentum ratio air m  = air mass flow rate, g/s P f m ,  = fuel mass flow rate on the pilot system, g/s MP f m ,  = fuel mass flow rate on the multipoint system, g/s p' = acoustic pressure, Pa p = averaged pressure, Pa q' = unsteady heat release, W/m 3 Ra = local Rayleigh index T = instability cycle period, s T air = air inlet temperature, K u' = acoustic velocity, m/

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On the request of CNES, ESA/ESTEC has led a study on the disposal of the hydrazine reservoirs of the Ariane 5 Attitude Control System (SCA). ESTEC has asked ONERA to propose an experimental assessment of risks of icing in piping and of generation of large debris in space during the process. After an examination of test conditions that would be representative of the reality, some campaigns have been realized at ONERA-Center of the Fauga-Mauzac. The objectives were the validation of the disposal system conceived for the SCA, also the general understanding of phenomena and consecutively a definition of the general trends to observe for ejection of liquids in space, and the constitution of a validation database for the modeling of hydrazine venting Validation tests of the flight ejector performed with hydrazine have demonstrated that the passivation process could be done without obstructing the piping. Further tests proved that this kind of phenomenon could be simulated without hazards by using water as similarity fluid. An effervescent type injector could be appropriate in order to guarantee a fine pulverization of a liquid ejected in a vacuum.