Abstract Direct injection (DI) strategy of natural gas (NG) into internal combustion engines (ICE) has led to higher thermal efficiency and lower exhaust emissions. In order to thoroughly understand the most relevant phenomena affecting the performances of such engines, computational fluid dynamics (CFD) plays a key role as an accurate description of the jet evolution and interaction within the combustion chamber is required to that aim. Accurate description of high-pressure gaseous jets is rather challenging at high Mach numbers, as the injected gas is strongly under-expanded once in the ambient, giving room to shocks due to compressibility effects. Also the interaction between shock waves and mixing layers needs to be carefully represented with a multi-dimensional model, calling for substantial computational resources requirements. In this paper a numerical investigation of the behavior of a gaseous jet (Argon) through an outward opening injector has been carried out. A Large Eddy Simulation (LES) approach has been used in order to track the structures derived by the interaction of the injected fuel with the surrounding ambient. Although already good results were obtained using a Reynolds Averaged Navier-Stokes (RANS) approach, the adoption of LES is required to characterize more accurately the jet properties in terms of vortex structures and mixing effectiveness. The effect of the Nozzle Pressure Ratio (NPR) on the jet evolution has been highlighted in the paper, showing how a higher NPR would give a faster injection process, compromising however the homogeneity of the mixture.

中文翻译：

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通过向外开口喷射器的气体射流：混合特性和湍流尺度的详细信息

摘要 天然气 (NG) 直接喷射 (DI) 到内燃机 (ICE) 的策略导致更高的热效率和更低的废气排放。为了彻底了解影响此类发动机性能的最相关现象，计算流体动力学 (CFD) 起着关键作用，因为为此目的需要准确描述燃烧室内的射流演变和相互作用。在高马赫数下准确描述高压气体射流是相当具有挑战性的，因为注入的气体一旦进入环境就会严重膨胀不足，由于可压缩性效应而给冲击留出空间。此外，冲击波和混合层之间的相互作用需要用多维模型仔细表示，这需要大量的计算资源。在本文中，对通过外开喷射器的气体射流（氩）的行为进行了数值研究。已使用大涡流模拟 (LES) 方法来跟踪由喷射燃料与周围环境相互作用得出的结构。尽管使用雷诺平均纳维-斯托克斯 (RANS) 方法已经获得了良好的结果，但需要采用 LES 来更准确地表征涡流结构和混合效率方面的射流特性。论文中强调了喷嘴压力比 (NPR) 对射流演变的影响，显示了更高的 NPR 如何提供更快的喷射过程，但会损害混合物的均匀性。