Liquid-Fuel Behavior in an Aeronautical Injector Submitted to Thermoacoustic Instabilities

The 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/s

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