Abstract Water-in-oil (W/O) emulsified fuel is a promising alternative fuel by inducing flash boiling of water at high temperature that can improve the atomization of fuel spray. The heating and evaporation process of emulsified fuel droplet is affected by the diffusion and coalescence of small dispersed water droplets in oil during the heating. In this study, a model is developed for the droplet heating and evaporation of W/O emulsified fuel with these key physics considered. The diffusivity of dispersed water droplets in oil is calculated using the Stokes-Einstein equation. The deactivation temperature of surfactant is selected as a criterion for the water coalescence since the water coalescence is due to the deactivation of surfactant. The process of water coalescence is simplified that the dispersed water droplets coalesce into one single water sub-droplet at the center of the oil droplet instantly as the droplet temperature reaches the deactivation temperature of surfactant. The model is validated against experimental data of single droplet under different heating temperatures, surfactant concentrations, and sizes of dispersed water droplets. Based on the proposed model, the effects of fuel properties and heating conditions on the droplet heating and evaporation are analyzed.

中文翻译：

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油包水型乳化燃料液滴加热蒸发模型

摘要 油包水（W/O）乳化燃料是一种有前景的替代燃料，它可以在高温下引起水的闪沸，从而改善燃料喷雾的雾化。乳化燃料液滴的加热蒸发过程受加热过程中油中分散的小水滴扩散和聚结的影响。在这项研究中，我们开发了一个模型，用于 W/O 乳化燃料的液滴加热和蒸发，并考虑了这些关键物理。使用 Stokes-Einstein 方程计算油中分散水滴的扩散率。选择表面活性剂的失活温度作为水聚结的标准，因为水聚结是由于表面活性剂的失活。水的聚结过程被简化为当液滴温度达到表面活性剂的失活温度时，分散的水滴在油滴中心立即聚结成单个水子滴。该模型针对不同加热温度、表面活性剂浓度和分散水滴尺寸下的单个液滴的实验数据进行了验证。基于所提出的模型，分析了燃料特性和加热条件对液滴加热和蒸发的影响。