Understanding the Causes of Liquid Jet Atomization

尽管电气化，特别是汽车电气化的加速发展，但全球对液体燃料（生物衍生或石油基）的依赖仍然很强。随着这些燃料的持续使用，需要持续改进污染物减少和燃料经济性。一个关键的地方看这些进步是直接在燃料喷射和喷雾形成的过程中。这一研究领域并不新鲜，但不幸的是，它面临着艰巨的实验挑战，这是由于在喷雾形成的早期阶段，液体燃料核心周围存在一团稠密的微小液滴。正是燃料喷射的这个早期阶段对所产生的喷雾特性至关重要，并且最终与燃料经济性和污染物形成相关的问题有关。一个有吸引力的替代方案正在追求在拟议的工作是使用高度详细的计算机模拟，可以充分询问所有阶段的喷雾形成具有足够的空间和时间分辨率。有了这些工具，长期存在的问题，喷雾形成的动力学和它们的敏感性，燃油性能和喷射策略将得到解决。一个关键的问题，在拟议的工作中关注最近观察到的液体燃料破碎的模式，这似乎暗示了一些普遍的行为，早期阶段的喷雾发展。如果能够理解这些模式，就有可能控制和优化它们，以最大限度地减少污染物排放和提高燃油经济性。这项工作旨在揭示液体射流破碎的根本原因，并通过计算机模拟为这个相对古老的问题提供一个新的视角。初步模拟结果表明，出现了一个大规模的蜿蜒模式，负责完整的液核的雾化，并与最大的生产界面面积和相间的动量交换。因此，所提出的工作的主要部分开始定量检查这种大规模的模式。这种模式的增长和其他界面扰动的解释，然后将追求与一般的不稳定性理论和基于势流理论的数学描述（完整的液体核心是很大程度上无旋）。为了对破碎现象进行更全面的分析，还将包括对喷射器喷嘴上游流动的模拟。这种上游调节的流动已被确立为界面不稳定性和射流破碎的发展中的一个关键特征。由于采用界面捕获方法模拟液体喷雾存在挑战，因此将进行新的验证练习，沿着一种自动化方法，用于评估所采用数值分辨率的适当性。

In spite of the accelerated development of electrification, particularly for automobiles, the global reliance on liquid fuels (bio-derived or petroleum based) continues to be strong. With the ongoing use of these fuels, a need exists for sustained improvements in pollutant reduction and fuel economy. A key place to look these advancements is directly in the process of fuel injection and spray formation. This area of investigation is not new, but unfortunately it has faced daunting experimental challenges originating from the presence of a dense cloud of minuscule droplets surrounding the liquid fuel core in the early stages of spray formation. It is precisely this early stage of fuel injection that is critical in the resulting spray characteristics and is ultimately linked to issues related to fuel economy and pollutant formation. An attractive alternative being pursued in the proposed work is the use of highly-detailed computer simulations that can adequately interrogate all stages of spray formation with sufficient spatial and temporal resolution. With these tools, long-standing questions concerning the dynamics of spray formation and their sensitivity to fuel properties and injection strategies will be addressed. A key question targeted in the proposed work concerns recently observed patterns of liquid fuel breakup, which seem to hint at some universal behavior of early-stage spray development. If these patterns can be understood, there is potential for controlling and optimizing them for maximum reduction of pollutant emissions and improvements in fuel economy. The proposed work aims to uncover the underlying causes of liquid jet breakup and provide a newer perspective to this relatively old problem by employing computer simulations. Preliminary simulation results have shown the emergence of a large-scale sinuous mode that is responsible for the atomization of the intact liquid core and is associated with the largest production of interfacial area and interphase momentum exchange. Hence, the main part of the proposed work begins with a quantitative examination of this large-scale mode. Explanation of the growth of this mode and other interfacial disturbances will then be pursued with a general instability theory and with a mathematical description based on potential flow theory (the intact liquid core is largely irrotational). To provide a more comprehensive analysis of the breakup phenomena, the simulation of the flow upstream of the injector nozzle will also be included. This upstream conditioning of the flow has been established as being a key feature in the development of interfacial instabilities and the breakup of the jet. Due to the challenges involved in the simulation of liquid sprays with interface capturing methods, new validation exercises will be undertaken, along with an automated means of evaluating the appropriateness of the numerical resolution employed.