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A series of studies on laminar flame propagation in off-stoichiometric dilute sprays of monodispersed inert or fuel drops had been investigated by large activation energy asymptotics. The present study extends previous theoretical model to consider water/octane core/shell structured drops instead of single-phase drops. The core/shell structured drops are composed of core fluid (water) encased by a layer of shell fluid (n-octane). In this study, we only deal with the case that core/shell structured drops are vaporized completely just at flame location. Namely, the discussions of this paper are restricted to the completely prevaporized mode. By varying parameters of core water radius, core-to-shell ratio, the amount of liquid loading, and the stoichiometric ratio (lean or rich burning), we examine the gasification of core water and shell fuel of core/shell structured drops upstream of the bulk flame and its relation to the internal heat transfer. The effects of drop radius, core-to-shell ratio, liquid loading, and overall heat loss or gain on flame propagation flux are reported and discussed.

An experimental system for observing the drop vaporization and microexplosion characteristics of emulsified droplets in high-temperature environments was conducted to analyze the effects of environmental temperature, droplet size, and water content on droplet behavior. In addition, emulsified low-sulfur heavy fuel oil (HFO) with a 20 vol% water content and pure low-sulfur HFO were used as fuels for burning in an industrial boiler under normal operating conditions. The results showed that by using an emulsified HFO with a 20 vol% water content, the boiler efficiency can be improved by 2%, and that a reduction of 35 ppm in NO x emissions (corresponding to a NO x reduction rate of 18%) can be achieved. These advantages are due to the occurrence of a microexplosion during the combustion of the emulsified droplets. It was observed that when emulsified HFO with a 20 vol% water content was used, the fuel (HFO) consumption rate was 252 l/h. On the other hand, the fuel consumption rate was 271 l/h when pure low-sulfur HFO was used. Therefore, a reduction of 19 l/h in the fuel (HFO) consumption rate was achieved when using the water-in-oil emulsion, corresponding to fuel savings of 7%.