Abstract Gasoline direct injection engines are highly dependent on the spray performance and associated combustion quality. The spray formation depends on many factors, namely internal flow characteristics, injection conditions, ambient conditions and fuel properties. There have been many studies performed to obtain a better understanding of these factors in recent years. In contrast to the others, studies on the internal flow characteristics are often performed numerically, as such, relevant experimental data is still lacking. Experimental investigations of the internal flow, such as flow turbulence, velocity distribution and cavitation are especially challenging under realistic conditions. Therefore, these conditions are generally simplified to diminish the demand for specialized experimental equipment and facilitate the measurements. In this regard, experimental data under relevant conditions are of high interest in the spray community. This work is focused on the internal flow study of multi-hole transparent nozzles under transient conditions at 1:1 geometrical scale. Injection pressure up to 100 bar is applied. The formation and development of string cavitation inside the nozzle hole are observed and presented in detail. For that, a novel ultra high-speed imaging technique at 5 MHz is applied. This technique in combination with the micro particle image velocimetry method, is then able to help to produce the velocity distribution of the internal flow. The velocity data is used further to reconstruct the pressure inside the nozzle by applying the Reynolds-averaged Navier–Stokes equations. Thus, the unique experimental data for the pressure distribution of the liquid fuel is obtained. Graphic abstract

中文翻译：

---

透明真实尺寸 GDI 喷嘴内流场和管柱空化的实验研究

摘要 汽油直喷发动机高度依赖于喷雾性能和相关的燃烧质量。喷雾形成取决于许多因素，即内部流动特性、喷射条件、环境条件和燃料特性。近年来，为了更好地了解这些因素，进行了许多研究。与其他研究相比，内部流动特性的研究通常是通过数值进行的，因此仍然缺乏相关的实验数据。内部流动的实验研究，例如流动湍流、速度分布和空化，在现实条件下尤其具有挑战性。因此，这些条件通常被简化以减少对专用实验设备的需求并促进测量。在这方面，喷雾界对相关条件下的实验数据非常感兴趣。这项工作的重点是在 1:1 几何尺度的瞬态条件下多孔透明喷嘴的内部流动研究。注射压力高达 100 bar。详细观察和呈现了喷嘴孔内串空化的形成和发展过程。为此，应用了一种新型的 5 MHz 超高速成像技术。这种技术与微粒图像测速方法相结合，然后能够帮助产生内部流动的速度分布。通过应用雷诺平均 Navier-Stokes 方程，速度数据进一步用于重建喷嘴内的压力。因此，获得了液体燃料压力分布的独特实验数据。图形摘要