Partially premixed flame structure and stability of twin droplets in flows

A study on the flame structure and stability, as well as the vaporization rates of twin 100 μm-dia n-octane droplets exposed to a high-temperature, partially premixed flow, was carried out. Two critical parameters of the Reynolds number and ambient equivalence ratio were accounted for to consider the influence of fuel vapor in the upstream far field on those of burning mechanisms around the twin droplets. When increasing the ambient equivalence ratio, chemical reactivity in the upstream could be classified into three kinds, i.e., weakly, moderately, and obviously reactive flows, according to the distribution of the vaporization rate of the leading droplet vs the Reynolds number. In moderately reactive flow, a double-peak profile was observed in the vaporization rate of the leading droplet. It showed that by increasing the Reynolds number the vaporization was sequentially dominated by the envelope flame, reactive flow, and convective flow. With regard to the trailing droplet, the impact of the ambient equivalence ratio on the vaporization rate distribution was comparable due to the multiple effects stemming from the leading droplet. The twin droplets behaved as a single droplet in the purely oxidizing environment. Partially premixed flow was conducive to promoting the vaporization and aided the flame stability in a twin-droplet system, while some burning properties in a counterflow system could also be realized in front of the leading droplet.