Understanding the Causes of Liquid Jet Atomization

尽管电气化加速发展，尤其是汽车，但全球对液体燃料(生物衍生燃料或石油燃料)的依赖仍然很强。随着这些燃料的持续使用，有必要持续改善污染物的减少和燃料经济性。观察这些进步的一个关键地方是直接在燃油喷射和喷雾形成过程中。这一研究领域并不新鲜，但不幸的是，它面临着令人望而生畏的实验挑战，这是因为在喷雾形成的早期阶段，液体燃料核心周围存在密集的微小液滴。正是燃油喷射的这一早期阶段对所产生的喷雾特性至关重要，并最终与燃油经济性和污染物形成有关的问题联系在一起。在拟议的工作中正在寻求的一个有吸引力的替代方案是使用高度详细的计算机模拟，该模拟可以以足够的空间和时间分辨率充分地询问喷雾形成的所有阶段。利用这些工具，将解决有关喷雾形成动力学及其对燃料特性和喷射策略的敏感性的长期存在的问题。拟议工作中针对的一个关键问题与最近观察到的液体燃料分解模式有关，这些模式似乎暗示了早期喷雾发展的一些普遍行为。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改善燃料经济性。这项拟议的工作旨在揭示液体射流破裂的根本原因，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，大尺度弯曲模式的出现是导致完整液核雾化的原因，并与最大的界面面积产生和相界面动量交换有关。因此，拟议工作的主要部分从对这种大规模模式的量化审查开始。然后将用一般不稳定性理论和基于势流理论的数学描述来解释这种模式的增长和其他界面扰动(完整的液核基本上是不旋转的)。为了对破碎现象进行更全面的分析，还将包括对喷嘴上游流动的模拟。这种流动的上游调节已被确定为界面不稳定性发展和射流破裂的关键特征。由于使用界面捕捉方法模拟液体喷雾所涉及的挑战，将进行新的验证练习，以及评估所采用的数值分辨率的适当性的自动化手段。

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.