Partially Premixed Flame Structure and Stability of Twin Droplets in Flows

Abstract

The flame structure and stability, as well as the vaporization rates of twin droplets exposed to a high-temperature, partially premixed flow are investigated in the present study. Two important parameters of the Reynolds number and ambient equivalence ratio are taken into consideration to account for 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, the chemical reactivity in the upstream can be classified into three types; weakly, moderately, and obviously reactive flows, according to the distribution of the vaporization rate of the leading droplet versus the Reynolds number. In particular, if the flow is moderately reactive, say, ϕ=0.2, a double-peak profile is observed in the vaporization rate of the leading droplet, and it clearly depicts that by increasing the Reynolds number the vaporization is sequentially dominated by the envelope flame, reactive flow, and convective flow. With regard to the trailing droplet, because of the multiple effects stemming from the leading droplet, the impact of the ambient equivalence ratio on the vaporization rate distribution is similar, except for in the purely oxidizing environment in which the twin droplets behave as a single droplet. As a whole, the evaluated results illustrate that the partially premixed flow is conducive to promoting the vaporization and aides the flame stability in a twin-droplet system, while some burning characteristics in a counterflow system can also be obtained in front of the leading droplet. [S0022-1481(00)01504-8]