Abstract
Experiments on ignition of droplet matrix are conducted by use of the drop shaft in the Microgravity Laboratory of Japan (MGLAB), whose test duration is about 5 seconds. When ignition time is very short, the change of droplet diameter is quite small and so quasi-droplets which are made of porous ceramics soaked with decane or hexadecane are available. Here we used quasi-droplets instead of real droplets, because making many droplets with an equal small size is quite difficult. At the commencement of the drop, the droplet matrix is moved into a chamber heated electrically in advance. The matrix is suddenly exposed to strong radiation and its ignition is induced. Ignition time depended on the droplet size and the spacing. When the size was large, ignition time decreased monotonously as the spacing became large, because the larger the spacing the less the thermal interaction between droplets . As the droplet size was small, however, ignition time took a minimum at a certain spacing and after that ignition time approached the ignition time of single droplet, in similar to the case of droplet array in the previous paper. The tendency of ignition time in normal gravity was very complex because of natural convection. OH emission images taken by CCD camera with an imageintensifier showed a group ignition in microgravity rather than ignition of an individual droplet in normal gravity.
