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.

该项目开发和演示了一种独特的，门控，皮秒，数字全息系统，用于成像液滴密集喷雾的详细结构。 密集喷雾通常存在于柴油和燃气涡轮机发动机中，以及用于食品和药品生产的喷雾干燥过程中。 了解喷雾系统中的控制行为在很大程度上取决于识别发生在喷雾核心处的过程，在喷雾核心处，大量液体分解成韧带和液滴。 密集的喷雾使得识别这些过程具有极大的挑战性，因为它们在光学上是厚的，使得难以从喷雾深处获得任何图像信息。 该项目的创新之处在于采用数字全息术和皮秒选通相结合的方法来限制光学噪声的数量，从而能够通过光学致密介质实现高分辨率的3D成像。 该方法有效地推广了现有的伪弹道成像系统，其中选择性地收集以相对较少的近前向散射相互作用穿过喷雾的光子，而拒绝那些以广角多次散射的光子。 数字全息术通过相干滤波进一步增强了光子选择。 为了将弹道光子和全息成像联合收割机结合，我们利用激光脉冲，该激光脉冲足够短以增强弹道光子检测并且足够长以允许具有可接受的空间分辨率的全息记录。 激光输出被分成三个不同的光束：1）控制克尔盒光开关的光束，2）物体光束，以及3）全息图的参考光束。 克尔盒提供光子定时选择性。 它被调整为刚好在全息脉冲到达之前打开。这两个脉冲的重叠时间决定了有效的选通时间。 当克尔门打开时，物波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提供对三维样品体积中所有颗粒的结构的详细观察。 结果将有助于识别诊断的局限性，并将产生有用的数据比较喷雾建模。 剩下的工作将致力于通过应用设计规则来优化系统，以量化权衡和优化未来的现场测量。这种新的诊断将允许现有技术无法实现的密集喷雾的三维成像。 这种新的测量能力有可能产生急需的数据喷雾形成和韧带断裂的理解和建模的喷雾物理。 例如，重质燃料的喷雾行为是决定许多装置的燃烧效率的控制过程。 虽然喷雾物理学已经研究了几十年，但在喷雾破碎和喷嘴附近燃料分布的精确建模方面仍然存在显著的局限性。 几乎没有近场成像数据。 这项工作结合了噪声抑制方面的弹道成像与数字全息产生一个演示仪器能够解决需要近场，三维成像数据在密集的喷雾。 大学？与Metrolaser，Inc.这一项目所包含的内容将大大加强研究工作，使其重点更加明确，同时使其范围扩大，超出纯粹的学术活动。 其结果将是有益的杠杆作用，对发展一个商业上可行的诊断仪器，所期望的和所需要的喷雾和燃烧社区。