Effects of varying forced convection on single and twin droplets combustion in microgravity

The objective of this study is to investigate the elementally process of turbulent spray combustion. We focused on the interaction between droplet flames in spray combustion and vortex tubes which compose turbulent flows, and simulated the interaction when varying forced convection to a standstill droplet was provided based on the model we proposed previously. To perform the experiments, varying flow which is received by the droplet moving through vortex tube was estimated using numerical calculation. Moreover, three non-dimensional numbers were used and characterization of varying relative flow and extension of scales keeping the analogy were made. The experiments were performed under microgravity. Observations of burning droplets were conducted using back-lit images recorded by a high-speed video camera. Using all of these images, histories of the instantaneous burning rate constant, K_i, were measured. Combustion experiments of single and an array of two droplets were performed. In single droplet experiments, it has been succeeded to measure the change of K_i caused by varying flow velocity. In the combustion experiments of an arrayed two droplets, it was found that the K_i of downstream droplet was decreased by the existence of upstream droplet. Moreover, the reduction effect of upstream droplet toward downstream droplet is depressed by varying flow direction, indicating that varying flow direction is effective to increase the K_i of downstream droplet.