Streamwise interaction of burning drops

The spatial distribution of drops and their interactions are influential parameters in spray combustion. Most available researches on this subject were about lateral spacing or were performed in micro-gravity. Studies about upstream/downstream convective interaction of burning drops are scarce. In this study, drop strings of different spacing were investigated in a high-temperature oxidizing environment for their flame transition, flame width variation and drop evaporation rate. The flame transition showed that along the flow direction, the drop flame initially located ahead of the drop, became a spherical envelope flame, then moved behind the drop, and finally burned as a wake flame. It was found that a drop string with an initial drop spacing (Si) of 2.5 or 5 was surrounded by a bulk flame tube, exhibited local group burning and soot layer. In addition, for Si = 2.5, spacing instability and collision merging of the burning drops occurred; the wake flame stretched away from the drop could attach to and stabilize on the rear drop. In the experiment, for all cases, most of drops in the string were not surrounded by the flame. For Si < 30, the drop evaporation rate was lower than that of a single drop. For 30 < Si < 75, the drop evaporation rate was higher than that of a single drop. The interaction of drops diminished if Si was more than 75.