Group Combustion Excitation in Randomly Distributed Droplet Clouds Based on Flame-spread Characteristics with Two-droplet Interaction in Microgravity

Experiments of flame-spread of fuel droplets have been performed in microgravity actively. However, the experiment has limitation in the number of droplets due to relatively short microgravity durations in the ground based facilities. It is difficult to conduct flame spread experiments of large scale droplet clouds in microgravity. This study conducted simulation of flame-spread behavior in randomly distributed large-scale droplet clouds by using a percolation approach, in order to make a theoretical link the gap between droplet combustion experiments and spray combustion phenomenon with considering two-droplet interaction. Droplets are arranged at lattice points in 2D lattice. The occurrence probability of group combustion (OPGC) is calculated as a function of the mean droplet spacing (S/d₀)_m. The (S/d₀)_m for 0.5 OPGC is defined as the critical mean droplet spacing (S/d₀)_critical, which separates the droplet cloud into two groups if the lattice size becomes infinity; relatively dense droplet clouds in which the group combustion is excited through flame spread and dilute droplet clouds in which the group combustion in is never excited. The results show that in 2D droplet arrangements, the (S/d₀)_critical considering two-droplet interaction is higher than that without considering two-droplets interaction.