Abstract The fuel spray injected into a direct injection (DI) engine is substantially affected by both the in-cylinder air flow and the piston cavity wall impingement. The combined effect of the air flow and the wall impingement plays an important role on the spray development, mixture formation, and subsequent combustion. In this study, the effects of cross-flow and flat wall impingement on the spray development and dispersion were investigated. The spray was injected by a valve covered orifice (VCO) nozzle under various cross-flow velocities and ambient pressures. Impingement spray images in a vertical plane and several horizontal planes were obtained by a high speed video camera and a continuous wave laser sheet. A high speed video camera connected with a long-distance microscope was employed to obtain the near-field spray images. The results show that cross-flow favors spray dispersion while the high ambient pressure tends to compress the spray profiles. Additionally, under an approximate liquid-to-air momentum flux ratio q , when the ambient pressure and cross-flow velocity were varied, at 2 ms ASOI the outlines of the spray in the windward side agree well, whereas the spray extended further in the leeward side at a lower ambient pressure. At the plane of y = 25 mm, a complex vortex movement was observed that resulted in a non-uniform distribution of droplets in the upper part of the spray in the leeward side. In addition, at the plane of y = 45 mm, an empty belt area occurred in the vortex core region revealing that the density of the droplets in this region was quite low. The quantitative analysis shows that with increasing cross-flow velocity, the spray tip penetration decreases slightly before impingement while the spray tip penetrates further on the wall surface after impingement. The high cross-flow velocity favors the spray breakup and dispersion leading to a larger wall-jet vortex while the high ambient pressure restrains the spray dispersion leading to a smaller spray tip penetration and vortex height. For near-field spray, the spray image at higher ambient pressure shows fewer ligaments. With increasing cross-flow velocity, the whole spray shifted downstream. The spray outline was wider at the initial stage (0.05 ms ASOI) than that at steady stage (2 ms ASOI) of spray evolution.

中文翻译：

---

高压错流条件下冲击喷雾及近场喷雾特性的实验研究

摘要 喷射到直喷 (DI) 发动机中的燃料喷雾受到缸内气流和活塞腔壁冲击的显着影响。气流和壁面撞击的综合作用对喷雾发展、混合物形成和随后的燃烧起着重要作用。在这项研究中，研究了横流和平壁冲击对喷雾发展和分散的影响。喷雾通过阀盖孔口 (VCO) 喷嘴在各种错流​​速度和环境压力下喷射。通过高速摄像机和连续波激光片获得垂直平面和几个水平平面的冲击喷雾图像。使用与远距离显微镜连接的高速摄像机来获取近场喷雾图像。结果表明，错流有利于喷雾分散，而高环境压力往往会压缩喷雾轮廓。此外，在近似的液气动量通量比 q 下，当环境压力和错流速度发生变化时，在 2 ms ASOI 时，迎风侧的喷雾轮廓非常吻合，而喷雾在迎风侧进一步延伸背风侧，环境压力较低。在 y = 25 mm 的平面上，观察到复杂的涡流运动，导致背风侧喷雾上部的液滴分布不均匀。此外，在 y = 45 mm 的平面上，涡核区域出现空带区域，表明该区域的液滴密度非常低。定量分析表明，随着错流速度的增加，喷嘴在撞击前的穿透力略有下降，而喷嘴在撞击后的壁面穿透更深。高错流速度有利于喷雾破碎和分散，导致更大的壁射流涡流，而高环境压力抑制喷雾分散，导致较小的喷嘴穿透和涡流高度。对于近场喷雾，较高环境压力下的喷雾图像显示较少的韧带。随着错流速度的增加，整个喷雾向下游移动。喷雾轮廓在初始阶段 (0.05 ms ASOI) 比在喷雾演变的稳定阶段 (2 ms ASOI) 更宽。高错流速度有利于喷雾破碎和分散，导致更大的壁射流涡流，而高环境压力抑制喷雾分散，导致较小的喷嘴穿透和涡流高度。对于近场喷雾，较高环境压力下的喷雾图像显示较少的韧带。随着错流速度的增加，整个喷雾向下游移动。喷雾轮廓在初始阶段 (0.05 ms ASOI) 比在喷雾演变的稳定阶段 (2 ms ASOI) 更宽。高错流速度有利于喷雾破碎和分散，导致更大的壁射流涡流，而高环境压力抑制喷雾分散，导致较小的喷嘴穿透和涡流高度。对于近场喷雾，较高环境压力下的喷雾图像显示较少的韧带。随着错流速度的增加，整个喷雾向下游移动。喷雾轮廓在初始阶段 (0.05 ms ASOI) 比在喷雾演变的稳定阶段 (2 ms ASOI) 更宽。