An experimental investigation of the heating behaviors of droplets of emulsified fuels at high temperature

Abstract

The secondary breakup of droplets of emulsified fuels induced by flashing boiling of its volatile component plays a vital role in improving fuel efficiency as well as reducing harmful emissions. In this study, the secondary breakup of heated water-in-oil emulsion droplets is investigated experimentally with a particular interest in the details inside the droplets. It is found that the breakup mode and strength are strongly correlated with the amount of water vaporized during the micro-explosion that is affected by the initial water content, the heating temperature and the size of the dispersed water droplet. The vaporized water was estimated from the temperature reduction during the micro-explosion based on mass and energy conservation. It is found that 20 vol% initial water content is optimum for the atomization of emulsified fuel under the heating temperature between 350 °C and 500 °C. The reason is that most of the left water in the droplet can vaporize explosively during the breakup that can induce a catastrophic micro-explosion with the most violent breakup strength. The breakup strength cannot be further increased at higher water contents, and it is inversely weakened at higher heating temperatures due to a large temperature gradient inside the droplet. In addition, it is also found that the effect of size of dispersed water droplet on the breakup mode and strength is not obvious compared with that of heating temperature and water content.