Brachial burning and gasification split of a convecting two-droplet system

Brachial burning and gasification-split characteristics of two droplets situated in a forced convection are analyzed by means of numerical method. For the given droplet size ratios of 1.5 and 0.25, it is found that a tri-brachial burning in the former and a penta-brachial burning in the latter are exhibited, where the brachial burning and gasification split are defined according to the envelope flame formation and destruction. When the droplet size ratio is large, the two droplets are always enclosed together in a flame for low Reynolds numbers. As Reynolds numbers are higher, the flame is destroyed and brought to the position behind the two droplets. Two or three gasification-split points are induced in accordance with the Reynolds number undergoing, thereby producing the tri-brachial burning. On the other hand, for a lower droplet size ratio such as 0.25, under certain conditions the flame surrounds only the trailing droplet, yielding a semienvelope flame. As a result, two extra brachial burning based on the variation of the semienvelope flame are defined, and the penta-brachial burning is obtained. Accordingly, the multiple burning states around two interactive droplets, including pure vaporization, wake flame, transition flame, envelope flame, and semienvelope flame, are established, except for the low Reynolds numbers in which only envelope flame develops. The new findings presented in the present article provide comprehensive insight for the development of droplet model in spray combustion, by intrinsically considering the variations of the Reynolds number around droplets.