Dynamical motion of Bunsen flame tip with flow rotation

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The dynamic motion of Bunsen flame tip with flow rotation has been investigated experimentally. The premixed mixture (methane/air mixture or propane/air mixture) is injected upwards from a tube burner with inner diameter 12 mm. The burner is rotated with arbitrary rotation speed. Since the honeycomb is installed in the burner, the flow rotation obtained can be assumed as a rigid body rotation. When the burner is not rotated (the Swirl number S=0), well known conical Bunsen flame is formed. When the Lewis number of the premixed mixture is more than unity, the cone shape flame shifts to the oscillating flame at around S=1.04 with increasing S. With further increase in S, the flame shifts to the plateau flame. The frequency of the flame tip motion decreases with increasing S. This is due to a decrease in the axial velocity with increasing the effect of centrifugal force by a flow rotation. The amplitude of the flame tip motion of the conical flame and plateau flame is as small as that of the conical flame without flame rotation, while that of the oscillating flame increases by a factor of five compared to the conical flame without flow rotation. This significant increase in the amplitude of the flame tip oscillation is due to the combined effect of the buoyancy force and the variation in flame intensity under the influence of the Lewis number. When the injection velocity from the burner and the rotating speed of the burner are increased, keeping S=1.04, the oscillating flame shifts to a quesi-oscillating flame. The quesi-oscillating flame shifts to a complex oscillating flame with further increase in the injection velocity and the burner rotating speed. The complex oscillating flame shows chaotic characteristics. These results elucidated that the time series chaotic analysis is useful to quantify characteristics of complex flame motion.