Experimental study of the morphology of two-phase flame instabilities in microgravity
Résumé
This paper reports experimental studies of cellular flames 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 behaviour, such as propagation speed and morphology. The main focus is to figure out on the interaction of the droplets with the propagating flame, and specifically on the possible correlation between the aerosol properties (i.e. droplets size and inter-distance) and the flame morphology. A high-speed shadowgraph technique is used along with a specific segmentation post-treatment to obtain a quantitative access to the flame propagation and morphology. In a second time, CH* chemiluminescence is used concurrently with high-speed ILIDS (Interferometric Laser Imaging for Droplet Sizing) or laser tomography 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. It is shown that it not only triggers the instability earlier, but that it also decreases the minimum size within the cell population. In addition to the minimum and maximum cell sizes, the distribution of cell size is provided, the extrema of which gives a reliable characteristic size of the cell population.