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Development of efficient and safe energy systems for space objects includes ensuring fire safety. This problem requires a deep understanding of influence of gravitational forces on combustion processes, which explains the importance of studying this issue. The paper analyzes the dynamics of inverted conical methane-air flame under conditions of normal and reverse gravitational force with external acoustic excitation. Applied frequencies of acoustic excitation could be parasitic or be produced during proper work of different technical systems of aircraft. High speed recording of flame chemiluminescence and PIV analysis were conducted. Decomposition of flow vector pictures into the modes was calculated using POD method. Energy contribution into the flow was analyzed for its separate elements at the different frequencies of excitation. At the high excitation frequencies vortex generation intensity in the shear layer with reverse gravity is about the same as it was observed in the experiments with normal gravity direction, that could indicate dominance of acoustic mechanism of the vortexes stimulation over the mechanism of shear instability. At external excitation frequency equals 240 Hz significant growth of shear vortex diameters and increasing of perpendicular oscillations amplitude of flame branches were obtained. Thereby in such experiment with 240 Hz external acoustic excitation the most intensive large scale instability of flow was observed. • The smallest vortices sizes are observed at 0 and 60 Hz excitation frequencies. • At excitation of 160, 240 and 420 Hz the vortices are non-affected by the gravity. • Vortice sizes and transverse oscillation range approach maximum at 240 Hz excitation. [ABSTRACT FROM AUTHOR]

Ensuring fire safety is one of the most important problems in the creation of habitable spacecraft. It is necessary to thoroughly study the issues of the reliability of the functioning of space systems, including those using chemical fuel. The paper studies experimentally the dynamics of an M-shaped premixed methane-air flame under normal and reversed gravity at various external acoustic excitation. The stable M-shaped flame is studied experimentally by means of high-speed video recording of flame chemoluminescence and PIV-methods. The paper shows that at low frequencies of acoustic excitation, the flame front remains practically undisturbed. At a 160 Hz frequency, the oscillatory motion is energetically more saturated than the main gas flow. With a further frequency increase, the main flow again becomes dominant in terms of energy, and the effect on the flame structure decreases. • Intense oscillations of the M-shaped flame occur when excited by acoustic oscillations of 160 Hz. • The intensity of forced oscillations rapidly decreases with an excitation frequency increase. • An external acoustics leads to a less regular flame front structure under reverse gravity. • The flame responds less intensely to external acoustic excitation under reverse gravity. [ABSTRACT FROM AUTHOR]