GOALI: Probing Dense Sprays with Gated, Picosecond, Digital Particle Field Holography

GOALI：利用门控、皮秒、数字粒子场全息术探测密集喷雾

• 批准号: 1233728
• 负责人: Derek Dunn-Rankin
• 金额: $ 32.7万
• 依托单位: University of California-Irvine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1233728&HistoricalAwards=false
• 关键词: GOALI; Probing; Dense; Sprays; Gated

This project develops and demonstrates a unique, gated, picosecond, digital holography system for imaging the detailed structure of dense sprays of liquid droplets. Dense sprays are commonly found in diesel and gas turbine engines, and in spray drying processes for food and pharmaceutical production. Understanding the governing behaviors in spray systems depends heavily on identifying the processes occurring at the core of the spray where the bulk liquid is breaking up into ligaments and droplets. Dense sprays make identifying those processes tremendously challenging because they are optically thick making it difficult to obtain any image information from deep within the spray. The innovation in this project is to employ a combination of digital holography and picosecond gating to limit the amount of optical noise sufficiently to enable high resolution, 3D imaging through an optically dense medium. The approach effectively generalizes existing pseudo-ballistic imaging systems, where photons that pass through the spray with relatively few near-forward scattering interactions are selectively collected while those scattered multiple times at wide angles are rejected. Digital holography further enhances the photon selection by coherence filtering. To combine ballistic photon and holographic imaging we utilize a laser pulse short enough to enhance the ballistic photon detection and long enough to allow holographic recording with acceptable spatial resolution. The laser output is split into three different beams: 1) a beam that controls a Kerr-cell optical switch, 2) an object beam, and 3) a reference beam for the hologram. The Kerr cell provides the photon timing selectivity. It is adjusted to open just before the holography pulse arrives. The overlap time of these two pulses determines the effective gating time. When the Kerr gate is open, the object and reference waves pass through and are recorded on the digital camera. An imaging approach of this form can provide a detailed look at the structure of all of the particles in a three-dimensional sample volume. Results will aid in identification of the diagnostic limitations and will produce data useful for comparisons to spray modeling. The remainder of the effort will be dedicated to system refinement via the application of design rules to quantify tradeoffs and optimization for future field measurements.This new diagnostic will allow three-dimensional imaging of dense sprays unachievable with existing techniques. This new measurement capability has the potential to produce much needed data on spray formation and ligament breakup essential for understanding and modeling of spray physics. For example, spray behavior of heavy fuels is a controlling process determining combustion efficiencies of many devices. While spray physics has been researched for decades, significant limitations still exist in accurate modeling of spray breakup and fuel distribution near the nozzle. Very little near field imaging data exists. This work combines the noise rejection aspects of ballistic imaging with digital holography to produce a demonstrated instrument capable of addressing the need for near field, three-dimensional imaging data in dense sprays. The university?industry collaboration with Metrolaser, Inc. that is included in this project will greatly enhance the research by refining its focus while simultaneously broadening it beyond a purely academic exercise. The result will be useful for leveraging towards the development of a commercially viable diagnostic instrument that is desired and needed by the spray and combustion communities.

该项目开发并展示了一个独特的，封闭式的，皮秒式的数字全息系统，用于成像液滴的密集喷雾剂的详细结构。 密集喷雾剂通常在柴油机和燃气轮机发动机中发现，以及用于食品和药物生产的喷雾干燥过程。 了解喷雾系统中的管理行为在很大程度上取决于识别喷雾核心的过程，其中散装液体正在分解成韧带和液滴。 密集的喷雾使识别这些过程非常具有挑战性，因为它们在光学上厚，因此很难从喷雾内部的深处获取任何图像信息。 该项目的创新是采用数字全息和皮秒门控的组合，以充分限制光学噪声的量，以使高分辨率通过光学密集的介质进行高分辨率。 该方法有效地概括了现有的伪球成像系统，其中通过相对较少的近乎前向散射相互作用的光子有选择地收集了喷雾剂，而拒绝以较大角度散射的光子被拒绝。 数字全息图进一步通过相干滤波增强了光子的选择。 为了结合弹道光子和全息成像，我们利用足够短的激光脉冲来增强弹道光子检测，并且足够长的时间允许以可接受的空间分辨率进行全息记录。 激光输出分为三个不同的光束：1）控制Kerr-Cell光学开关的光束，2）对象梁，3）全息图的参考光束。 Kerr单元提供了光子时序选择性。 在全息脉冲到达之前，它已调整为打开。这两个脉冲的重叠时间决定了有效的门控时间。 当Kerr门打开时，对象和参考波通过并记录在数码相机上。 这种形式的成像方法可以详细介绍三维样品体积中所有颗粒的结构。 结果将有助于识别诊断限制，并产生可用于对喷涂建模的比较的数据。 其余的努力将通过应用设计规则来量化权衡方案和对未来现场测量的优化，将其用于系统的完善。此新诊断将允许对现有技术无法实现的密集喷雾剂进行三维成像。 这种新的测量能力有可能生成有关喷雾形成和韧带破裂的急需数据，这对于理解和建模喷雾物理学必不可少。 例如，重燃料的喷雾行为是确定许多设备燃烧效率的控制过程。 尽管已经研究了数十年的喷雾物理学，但在喷嘴附近的喷雾分解和燃料分布的准确建模中仍然存在重大局限性。 很少有近场成像数据存在。 这项工作将弹道成像的噪声排斥方面与数字全息图结合在一起，以生成一种能够满足近场，三维成像数据的仪器。 该项目中包含的大学工业与Metrolaser，Inc。的合作将通过完善其焦点，同时将其扩大到纯粹的学术练习之外，从而大大增强研究。 结果对于利用喷雾和燃烧社区所需和需要的商业可行诊断工具的开发将很有用。