The flow and cavitation phenomena inside nozzle sac play an important role in the fuel atomization process, especially at the end of the injection, which may cause high-temperature gas ingestion consequently leading to coke formation inside the orifice. It is of great difficulty to reveal the flow and cavitation morphology inside fuel nozzles during the fuel injection process since the nozzle sac is enclosed by thick steel wall and the whole process takes place in a few microseconds. Therefore, a dedicated synchrotron radiation X-ray phase contrast imaging technology was developed by optimizing sample to detector distances and image processing methods, and the image intensity and contrast were enhanced to visualize the transient cavitation morphology. The flow and cavitation morphology at three different injection pressures were recorded and compared. The results show that the cavitation bubbles and gas ingestion process inside nozzle sac can be clearly observed revealing a two-stage flow dynamics process occurring inside the sac. At the first stage, the cavitation bubbles appear in the sac around the needle tip surface due to the sudden pressure decrease; at the second stage, the ambient gas was ingested through the orifice due to the increase of the vacuum degree in the sac, leading to rapid burst of the cavitation bubbles. The ingested gas replacing the cavitation bubbles then occupy the most space of the sac at the end of the injection.

中文翻译：

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利用同步辐射X射线相衬成像技术了解高压喷嘴中的瞬态内部流动过程

喷嘴囊内部的流动和气蚀现象在燃料雾化过程中起着重要作用，尤其是在喷射结束时，这可能会导致高温气体摄入，从而导致孔内形成焦炭。揭示燃料喷射过程中燃料喷嘴内部的流动和气蚀形态是非常困难的，因为喷嘴囊被厚的钢壁包围，整个过程发生在几微秒内。因此，通过优化样品到检测器的距离和图像处理方法，开发了专用的同步辐射X射线相衬成像技术，并增强了图像强度和对比度以可视化瞬时空化形态。记录并比较了三种不同注射压力下的流动和空化形态。结果表明，可以清楚地观察到喷嘴囊内部的空化气泡和气体吸收过程，揭示了囊内发生的两阶段流动动力学过程。在第一阶段，由于突然的压力降低，空化气泡出现在针尖表面周围的囊中。在第二阶段，由于囊中真空度的增加，环境气体通过孔口被吸入，导致空化气泡迅速破裂。注入的气体取代了空化气泡，在注入结束时占据了囊的最大空间。结果表明，可以清楚地观察到喷嘴囊内部的空化气泡和气体吸入过程，揭示了囊内发生的两阶段流动动力学过程。在第一阶段，由于突然的压力降低，空化气泡出现在针尖表面周围的囊中。在第二阶段，由于囊中真空度的增加，环境气体通过孔口被吸入，导致空化气泡迅速破裂。注入的气体取代了空化气泡，在注入结束时占据了囊的最大空间。结果表明，可以清楚地观察到喷嘴囊内部的空化气泡和气体吸入过程，揭示了囊内发生的两阶段流动动力学过程。在第一阶段，由于突然的压力降低，空化气泡出现在针尖表面周围的囊中。在第二阶段，由于囊中真空度的增加，环境气体通过孔口被吸入，导致空化气泡迅速破裂。注入的气体取代了空化气泡，在注入结束时占据了囊的最大空间。由于囊中真空度的增加，周围的气体通过孔口被吸入，导致空化气泡迅速破裂。注入的气体取代了空化气泡，在注入结束时占据了囊的最大空间。由于囊中真空度的增加，环境气体通过孔口被吸入，导致空化气泡迅速破裂。注入的气体取代了空化气泡，在注入结束时占据了囊的最大空间。