Spray impingement wall film breakup by wave entrainment
Spray impingement wall film breakup by wave entrainment
复制标题
波夹带导致喷雾冲击壁膜破裂
DOI：
10.1016/j.proci.2018.07.101
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发表时间：
2019
影响因子：
3.4
通讯作者：
Xu Min
中科院分区：
文献类型：
--
作者：
Li Xuesong;Pan Hujie;Dong Xue;Hung David;Xu Min
火花点火直喷（SIDI）工况下，燃油喷雾对发动机壁面和活塞的撞击是影响发动机排放和燃烧效率的主要因素。过多的壁膜将导致发动机摩擦的恶化、不完全燃烧和相当大的循环间变化。这些影响在发动机冷起动过程中更为明显。因此，研究发动机壁面/活塞壁面油膜的形成过程以及油膜与撞击喷雾和喷雾诱导气流相互作用的动力学过程，对减少壁面油膜质量具有重要意义。然而，现有文献对壁膜的动态过程研究不够深入。这项工作将提出一个高速，同时测量的单孔喷雾结构，以及壁膜的几何形状和厚度，通过米氏散射和体积激光诱导荧光，分别。通过用已知的楔形液膜装置进行荧光强度信号校准来实现定量膜厚度测量。在测量中发现了液膜波前缘处的显著壁膜液滴夹带，这在现有的喷雾撞击研究中还没有得到充分的描述或分析。大量的液滴通过液膜指进脱离液膜，在此过程中，壁面上的液体质量减少。对这种现象进行了定量分析，我们估计，相当于30-40%的残留液膜质量的液体质量通过波夹带从液膜分离。此外，通过对喷雾与液膜碰撞后的侧视图进行对比研究，发现喷雾结构的不均匀性可能是液膜波动的原因。这些观察结果表明，波卷吸应考虑数值模型和实验设计，以准确预测喷雾碰撞现象。(C)2018燃烧研究所爱思唯尔公司出版All rights reserved.
Fuel spray impingement on engine wall and piston in the spark-ignition direct-injection (SIDI) setting has been considered a major concern in the aspect of engine emission and combustion efficiency. Excess wall film will result in deterioration of engine friction, incomplete combustion, and substantial cycle-to-cycle variations. These effects are more pronounced during engine cold-start process. Therefore, the formation of wall film on engine wall/piston and the dynamic process of the wall film interacting with impinging spray and spray-induced gas flow are of great significance for reducing wall film mass. However, the dynamic process of wall film was not investigated thoroughly in existing literatures. This work will present a high-speed, simultaneous measurement of a single-hole spray structure, as well as wall film geometry and thickness, via Mie scattering and volumetric laser-induced fluorescence, respectively. Quantitative film thickness measurement was achieved via fluorescence intensity signal calibration with a known, wedge-shape liquid film apparatus. Remarkable wall film droplet entrainment at the leading edge of the liquid film waves was revealed in the measurement, which has not been adequately depicted or analyzed in existing spray impingement studies. A considerable amount of liquid droplets detaches from the liquid film via liquid film fingering, during which process the quantity of liquid mass on the wall is decreased. Quantitative analysis of such phenomenon is performed and we estimated that a liquid mass equivalent to 30-40% of the residual liquid film mass is detached from the liquid film via wave entrainment. Furthermore, through the comparative study of the side view of the spray and the liquid film caused by spray impingement, it is shown that non-uniform spray structure is likely the cause of liquid film wavy motions. These observations suggest that wave entrainment should be considered by numerical models and experimental designs to accurately predict spray impingement phenomenon. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.