Due to current and future environmental and safety issues in space propulsion, typical propellants for upper stage or satellite rocket engines such as the toxic hydrazine are going to be replaced by green propellants like the combination of liquid oxygen and hydrogen or methane. The injection of that kind of cryogenic fluids into the vacuum atmosphere of space leads to a superheated state, which results in a sudden and eruptive atomization due to flash boiling. For a detailed experimental investigation of superheated cryogenic fluids, the new cryogenic test bench M3.3 with a temperature controlled injection system was built at DLR Lampoldshausen. After a first test campaign with high-speed shadowgraphy of flash boiling liquid nitrogen sprays, a laser-based Phase Doppler system was set-up to determine the spatial distributions of droplet velocities and diameters in highly superheated sprays. The spatial distributions revealed a core region with high mean velocities close to the injector orifice. With increasing distance from the injector orifice, the sprays develop a more and more monodisperse pattern. These distributions also showed that atomization due to flash boiling generates finer sprays with growing degrees of superheat. In certain spray regions, two droplet populations varying in their direction of motion, velocity and diameter due to possible recirculation zones were observed. The experimental data of flash boiling liquid nitrogen generated within this study provide a comprehensive data base for the validation of numerical models and further numerical investigations.

中文翻译：

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通过相位多普勒诊断法测定闪蒸液氮射流中的液滴速度和直径分布

由于当前和未来空间推进中的环境和安全问题，用于上级或卫星火箭发动机的典型推进剂（如有毒肼）将被绿色推进剂（如液氧和氢气或甲烷的组合）所取代。将这种低温流体注入太空的真空气氛中会导致过热状态，从而由于闪沸而导致突然爆发的雾化。为了对过热低温流体进行详细的实验研究，在 DLR Lampoldshausen 建造了带有温控喷射系统的新型低温试验台 M3.3。在对闪蒸液氮喷雾进行高速阴影成像的第一次测试之后，建立了一个基于激光的相位多普勒系统来确定高度过热喷雾中液滴速度和直径的空间分布。空间分布揭示了靠近注入器孔口的具有高平均速度的核心区域。随着与喷射器孔口距离的增加，喷雾形成越来越单分散的模式。这些分布还表明，随着过热度的增加，由于闪蒸引起的雾化会产生更细的喷雾。在某些喷雾区域中，观察到由于可能的再循环区域而在运动方向、速度和直径上发生变化的两个液滴群。本研究中产生的闪蒸液氮的实验数据为数值模型的验证和进一步的数值研究提供了一个全面的数据基础。