EXPERIMENTAL STUDY OF THE MORPHOLOGY OF TWO-PHASE FLAME INSTABILITIES IN MICROGRAVITY

This paper reports experimental studies of cellular flame instabilities in the case of an expanding two-phase spherical flame under microgravity conditions. The presence of liquid fuel droplets leads to the triggering of those instabilities on the flame surface (cracks or cellular) which have an extensive impact on flame behavior, such as propagation speed and morphology. The main focus is to figure out the interaction of the droplets with the propagating flame. A high-speed shadowgraphy technique is used along with a specific segmentation posttreatment to obtain quantitative access to the flame propagation and morphology. In a second time, CH* chemiluminescence is used concurrently with high-speed interferometric laser imaging for droplet sizing or planar Mie scattering for a simultaneous characterization of the flame structure and aerosol properties. By a comparison with equivalent gaseous flames, the impact of the two-phase configuration is assessed. In addition, this study proposes a quantitative analysis of the cell size distribution over the flame propagation. It is finally shown that the size of the cells is not directly correlated with the droplet interdistance, which indicates that the droplets only act as a trigger for the development of the instabilities.