Direct-injection spark-ignition (DISI) engines, which have a better fuel economy than conventional gasoline engines, have been widely introduced in the market. However, in these engines, the rich air−fuel mixtures associated with fuel films during cold starts, caused by spray impingement, produce particulate matter. To predict soot formation, it is important to predict the mixture field precisely; thus, accurate spray and film models are prerequisites for creating a soot model. Previous wall impingement models were well matched with low Weber number collision conditions, such as those of diesel engines, which have relatively high ambient pressures and small Sauter mean diameters. In this study, the outliers of the previous model were observed to decrease as the collision distance increased and when a strong droplet dissipation occurred owing to a high ambient pressure. However, the kinetic energy in DISI engines is considerably larger than the dissipation energy calculated using the Weber number and surface tension; thus, the amount of dissipation energy should be determined within a realistic range. To analyze the two-dimensional (2D) spray-wall impingement phenomenon more accurately, a 2D child droplet generation was considered. Finally, the film and spray behaviors were measured to validate the SNU model. The Mie scattering images of the gasoline spray near the wall were captured to measure the rebound spray radius. Then, a laser-induced fluorescence with a total internal reflection was used to determine the film shape and thickness. Compared with existing models, the SNU model exhibits better agreement with the Mie experimental results without requiring case-dependent changes to the model constant. However, the film simulation part needs improvement in future work.

中文翻译：

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汽油直喷条件下喷雾壁冲击和燃料膜形成的建模

与传统汽油发动机相比，燃油经济性更好的直喷式火花点火（DISI）发动机已被广泛引入市场。然而，在这些发动机中，在冷启动期间与燃料膜相关的浓空气燃料混合物（由喷雾冲击引起）会产生颗粒物质。为了预测烟炱形成，准确预测混合场很重要；因此，准确的喷雾和薄膜模型是创建烟灰模型的先决条件。以前的壁面碰撞模型与低韦伯数碰撞条件非常匹配，例如柴油发动机，其具有相对较高的环境压力和较小的 Sauter 平均直径。在这项研究中，随着碰撞距离的增加以及由于高环境压力而发生强烈的液滴消散，观察到先前模型的异常值减少。然而，DISI 发动机的动能远大于使用韦伯数和表面张力计算的耗散能；因此，耗散能量的大小应在实际范围内确定。为了更准确地分析二维 (2D) 喷雾壁撞击现象，考虑了二维子液滴生成。最后，测量薄膜和喷雾行为以验证 SNU 模型。捕获靠近墙壁的汽油喷雾的 Mie 散射图像以测量回弹喷雾半径。然后，使用具有全内反射的激光诱导荧光来确定薄膜的形状和厚度。与现有模型相比，SNU 模型与 Mie 实验结果表现出更好的一致性，而无需对模型常数进行依赖于案例的更改。但是，电影模拟部分在未来的工作中需要改进。