超高速喷雾流场高时间分辨成像与诊断技术

Developing optical imaging technique for observation of ultra-high-speed spray flow field has very important significances for engine designs. However, traditional optical imaging techniques can not be applied to the near-field region of ultra-high-speed fuel spray of engines in the equipments such as rockets due to the huge turbulence and high density of droplets in this region. In this project, we propose by developing a ballistic light imaging technique with ultrafast optical Kerr gate to overcome the problems presented in current optical imaging techniques of studying the ultra-high-speed fuel spray flow field and realize high time-resolved imagings of particles in the near-field region of ultra-high-speed spray flow field. The study includes:. (1).Investigating multi-pulse ballistic imaging with ultrashort frame interval based on the polarization and wavelength division multiplexing in order to extend the ability of the ballistic imaging technique to measure the velocity and acceleration vectors of ultra-high speed particles.. (2).Improving the imaging resolution and signal-to-noise ratio of the optical imaging technque by combining the spatial filtering with the optical Kerr gate techniques, and eliminating the influence of self-diffraction effect on optical Kerr gate. . (3).Investigating two-photon laser induced fluorescence (LIF) technique, in which the accuracy of LIF detection for the combustion components will be improved significantly by eliminating the fluorescence quenching effect in LIF measurements.. The final goal is to exhibit an ultrafast optical Kerr gated ballistic light imaging system characterized by the optical density of OD>12, the temporal and spatial resolutions of TR<0.5 ps and SR<20 μm respectively, and the frame interval of FI<50 ps.

发展超高速喷雾流场光学成像技术，对发动机的设计具有重要意义。在火箭等发动机超高速燃料喷雾的近场区，由于射流湍流强度大、液滴密度高，通常的流场观测技术无法适用。本项目针对超高速燃料喷雾流场光学成像技术目前存在的若干问题，提出通过超快光克尔门选通弹道光技术，实现对近场区的高时间分辨成像；利用波分复用结合偏振复用的多脉冲曝光技术，实现超短帧间隔的弹道光成像，使弹道光成像技术的功能扩展至能够测量超高速流场中粒子运动速度和加速度；通过超快光克尔门和空间滤波技术的有机结合、以及抑制超快光克尔门中自衍射效应的干扰，提高成像分辨率和信噪比；研究双光子诱导荧光技术，通过抑制激光诱导荧光诊断中普遍存在的荧光淬灭效应，提高对燃烧产物浓度的测量精度。展示基于多脉冲曝光技术的超快光克尔门选通弹道光成像系统，实现散射介质最大光学密度大于12，成像时间和空间分辨率分别优于0.5ps和20μm，帧间隔优于50ps。

发展超高速喷雾流场光学成像技术，对发动机的设计具有重要意义。在火箭等发动机超高速燃料喷雾的近场区，由于射流湍流强度大、液滴密度高，通常的流场观测技术无法适用。本项目针对超高速燃料喷雾流场光学成像技术目前存在的若干问题，按照研究计划开展了超快光克尔门选通弹道光成像技术和飞秒光丝诱导分子荧光光谱探测技术研究。. 研究了飞秒时域光克尔门中超快光克尔效应与自衍射效应之间的竞争机制及其调控方法，通过调控泵浦光和探测光偏振态有效抑制了自衍射效应的产生，实现了高对比度超快光克尔门。研究了飞秒脉冲在散射介质中的传播规律，提出了外差光克尔门选通成像新方法，有效提高了成像分辨率和信噪比；提出了空间门选通超连续谱照明成像新方法，有效抑制了成像散斑。研制了适于燃料喷雾场诊断的超快光克尔门选通成像系统，系统成像时间分辨率优于200fs、空间分辨率优于5μm、光学深度大于12。. 研究了飞秒光丝诱导激射现象与机理，飞秒激光在气体、燃烧场传播效应和成丝规律，发现了飞秒光丝自产生白光种子注入空气激光现象。提出了飞秒成丝荧光自发射放大分子指纹光谱探测和火焰燃烧组分分析的远程探测新方法，有效地解决了传统激光诱导荧光光谱技术在燃烧场探测应用中荧光淬灭效应的影响，获得了燃烧过程中分子浓度与荧光强度之间的关系。研究了脂肪酸甲酯/柴油等高压共轨喷雾的宏观和微观特性，以及不同工况下汽油和四氢呋喃的喷雾特性和甲醇裂解气空气层流预混火焰的燃烧特性。. 项目研究成果发表学术论文62篇，其中发表在Nature Conmmunication, Applied Physics Letters, Optics Letters, Optics Express等期刊SCI收录论文56篇，获授权发明专利5项，国内和国际会议特邀报告9次，获陕西省科学技术奖一等奖1项。发动机燃料喷雾激光诊断领域著名专家瑞典隆德大学M. Linne教授在其发表在Prog. Energ.Combus. Sci.上的长篇综述论文中介绍了我们的研究成果，称赞我们的成果对燃料喷雾激光诊断技术是令人激动的发展。