雾化场光学全息与数字全息联合测量

针对雾化场光学全息测量存在干板湿化学处理繁琐、再现像采集耗时的问题,提出光学全息与数字全息联合测量的方法,建立由同轴光学全息、同轴数字全息以及数字延迟信号发生器组成的测量系统,并以双孔直射式喷嘴产生的雾化场为测量对象,利用该测量系统在一次测量中同时获得雾化场的光学全息和数字全息的再现图像,两者具有很好的一致性。光学和数字再现图像相对应的视场范围分别为27.87 mm4.77 mm和27.59 mm6.67 mm,数字方式获得视场范围内单一层面再现像的时间仅为8 s,而光学方式将近1 h。结果表明,光学全息与数字全息联合测量时,通过数字全息的雾化再现图像能够对实验总体效果进行实时评估,提高了雾化场全息测量的实验效率。     

Infrared thermography-based visualization of droplet transport in liquid sprays

An infrared thermography-based technique for the characterization and visualization of liquid sprays was developed. The technique was tested on two atomizers: a high-speed rotary bell atomizer and a high volume low pressure air-assisted atomizer. The technique uses an infrared thermography-based measurement in which a uniformly heated background acts as a thermal radiation source, and an infrared camera as the receiver. The infrared energy emitted by the radiation source in traveling through the spray is attenuated by the presence of the droplets inside the spray. The infrared intensity is captured by the receiver showing the attenuation in the image as a result of the presence of the spray. The captured thermal image is used to study detailed macroscopic features of the spray flow field and the evolution of the paint droplets as they are transferred from the applicator to the target surface.     

Ultra-lean limit extension for gasoline direct injection engine application via high energy ignition and flash boiling atomization

Extensive efforts have been made in achieving leaner combustion for gasoline direct injection (GDI) engines to further improve the thermal efficiency and reduce harmful emissions. Among these techniques, increasing ignition energy has been proven to be an effective method to achieve lean combustion. Few targets the atomization process of the fuel in generating a more homogenous fuel-air mixture, which is believed to be able to extend the lean flammability limit of the engine. This investigation explores the use of flash boiling atomization, a technique to improve spray atomization via elevating the fuel temperature, in combination with high energy ignition technique for better GDI engine performance under lean-burn conditions. For such purposes, a single-cylinder, optical GDI engine was used with high-speed imaging techniques, along with other measurement instruments. The fuel was preheated by a heating element and high energy ignitions were generated by a customized ignition system. ignitions with various initial currents (transistor coil ignition (TCI), 250 mA, and 500 mA) under both sub-cooled and flash boiling conditions were examined using different excess air ratios. It was found that using flash boiling atomization has extended the lean limit from 1.95 to 2.10 under the 500 mA initial current ignition. Other critical parameters such as indicative mean effective pressure (IMEP), emissions such as CO, NO_x, THC were also analyzed to demonstrate the impacts of high energy ignition and flash boiling atomization.     

An image-shifting technique based on grey-scale classification for particle image velocimetry

The image-shifting techniques are used to overcome the directional ambiguity of particle image displacement in the measurement of particle image velocimetry (PIV). This paper proposes an image-shifting technique based on grey-scale classification for PIV. By calculating the unified grey-scale statistical frequency of each interrogated unit, the directional ambiguity is resolved without any special requirement of the camera, and the particle image displacement is calculated synchronously. This image-shifting technique can be realized by controlling the difference in the light intensity of two lasers. Using this new technique, a PIV system was developed and used to measure the diesel spray flow. The displacement vector map of fuel particle in the spray flow was obtained, and the structure of the spray flow was investigated. The application confirmed that the image-shifting technique is viable and effective.     

A High Power,High Resolution LDA/PDA System Applied to Gasoline Direct Injection Sprays

A new generation LDA/PDA transmitter system has been designed and constructed. The heart of the optical system is a new type of Bragg cell. Advances in laser power handling and symmetrical splitting at high Bragg angles of the shifted and unshifted beams have made it possible to construct a simple yet elegant LDA/PDA transmitter. The optical system integrates the Bragg cell with a laser beam expander to offer variable beam separation and high beam expansion ratios to produce a measurement volume with a high spatial resolution and at high power levels. The transmitter is proving to be a significant contribution to LDA/PDA optical system design and, not only applicable as a research tool for use in flows of a demanding nature but, due to its simplicity, flexibility and cost, an asset to teaching. The LDA/PDA system is being applied to characterise the atomization of fuel by high pressure automotive injectors as found in Gasoline Direct Injection (GDI) engines. Although the PDA system was configured to measure two orthogonal velocity components (2D) and size, its operation was not restricted to this configuration. An analysis of the spray with the PDA system in 1D and size and the LDA system in 2D and 1D configurations indicated the complexity of the atomization and break-up processes occurring in the spray. Single-shot imaging was used to study the spatial structure of the spray as a function of time. Use of the light sheet imaging technique alone could lead to false impressions of the atomization process.     

基于机器视觉的圆孔尺寸测量系统研究

针对常见的圆形目标检测,开发了一套基于机器视觉技术的圆孔尺寸测量系统,采用混合噪声滤波、模糊和遗传边缘检测方法从采集的零部件图像中,提取出圆孔图像的边缘,通过插值圆度检测方法,精确测量出圆孔的半径、面积等特征参数。测试表明,测量系统的平均值误差为0.010 5 mm,远远低于人工测量的平均值误差0.027 3 mm,能够满足工业应用中的精确性要求。     

Experimental Analysis of the Response of a Laser/Phase Doppler Anemometer System to a Partially Atomized Spray

This work describes a systematic approach adopted to establish Laser and Phase Doppler Anemometry, LDA/PDA, experimental techniques that would allow velocity and dropsize measurements to be made over wide velocity and size ranges with confidence in partially atomized sprays. The analysis considers the sprays generated by different gasoline direct injection (GDI) systems injecting into air under atmospheric conditions. The upper limit to the dropsize range in the fuel sprays was confirmed using (a) an Oxford Lasers' VisiSizer and (b) droplets of a known size produced by a mono‐dispersed droplet generator. GDI fuel sprays are highly transient, optically dense and provide a high degree of penetration and atomization. The measurement problem is therefore one of the detection of small, high speed droplets inside a dense cloud of surrounding droplets. Furthermore, under the transients found at the start and end of injection and during high fuel loads, fuel elements in the form of sheets, ligaments and filaments are also injected. These liquid fuel elements subsequently break‐up, downstream from the nozzle, to form droplets of a much larger size class but with a much lower number density [1]. The co‐existence of these liquid fuel elements and the widely different size classes in the spray are considered to pose a problem for dropsize measurements by the PDA technique. In particular: the wide dynamic range of light intensities scattered by the fuel elements and droplets; the trajectory of large drops through the edges of the PDA measurement volume with its Gaussian intensity distribution [2] and the high probability of non spherical droplets. The work concludes that the LDA/PDA measurement technique, as applied here, is robust. It can discriminate between partially and fully atomized sprays, has a high probability of accurately measuring dropsizes larger than the measurement volume and give a realistic indication of ‘sizes’ for non spherical droplets. However, specification of the PDA system parameters must be strictly compatible with the measurement task to yield unambiguous results.     

Application of tangential geometry of the acousto-optical interaction to visualization of phase objects

A method of visualization of phase objects is described based on selective properties of the Bragg diffraction of light by ultrasound. The main attention is focused on specific features of visualization in tangential geometry of the acousto-optical interaction. It is shown that, in the optimized case, the light intensity distribution in the visualized image is proportional to the phase gradient. The resolution and contrast of the visualized image are analyzed numerically. Potentialities of the method are illustrated by examples of computer simulation of the visualization effect.     

基于45°反射导光镜的圆孔内壁图像检测方法研究

圆孔工件广泛应用于航空航天等精密制造领域,快速准确地对圆孔内壁图像进行检测是保证工件质量的重要手段。介绍了一种基于45°反射导光镜的圆孔工件内壁图像检测方法,该方法通过将反射镜伸入工件内部获取内壁局部图像,采用连续旋转工件与图像拼接方式获得内壁的完整图像。针对4.5 mm内径的工件设计并制作了一种45°反射镜,理论分析了有效成像区域以及平移和倾斜误差造成的影响。搭建了圆孔工件内壁检测装置,设计并制作了一种专用标定工件,实现了检测装置像素当量的标定。实验结果表明,检测装置的系统像素当量约为5 μm,测量相对误差小于3.5%。单幅图像的有效成像区域得到明显提高,通过拼接方法获得了工件内壁的完整图像。     

一维全场彩虹喷雾测量方法试验研究

全场彩虹技术受限于单点区域测量,如何拓展其到多点测量甚至一维测量,对于其实用性具有重要的意义。对提出的全场彩虹系统一维化原理进行了分析,设计并搭建了一维全场彩虹测量系统。分析了系统参数的选择对彩虹图像的影响,并改进了标定方法。用该系统对乙醇喷雾在一维线区域的蒸发物理过程进行了定量研究,得到的结果与PDA测量结果进行了对比,符合实际物理现象。     

分子过滤瑞利散射技术测量火焰温度和密度

 为了解决瑞利散射光易受米散射和背景杂散光干扰的问题,发展了结合窄线宽激光器、分子过滤器以及像增强器等技术的分子过滤瑞利散射技术。在图像诊断的基础上,依据测量的碘蒸气吸收光谱曲线,对CH₄/air预混火焰进行了诊断,获得了密度场和温度场分布。距炉面15 mm火焰中心区域处,分子过滤瑞利散射(FRS)技术测量的温度为1 827 K±84 K,密度为0.19 kg/m³,其测温结果与CARS法的测温结果基本吻合。最后分析了FRS技术测温不确定度。实验表明FRS技术具有较高的信噪比,可以定量测量温度和密度信息,有望应用于超音速燃烧流场、紊流场等复杂流场的诊断。     

基于机器视觉的微光夜视仪整机检测系统设计

设计并研制了微光夜视仪整机检测系统,采用CCD器件作为被检仪器输出图像的探测接收器,可在微光夜视仪完整状态下对像增强器进行检测。提出微光夜视仪整机状态下像增强器性能的检测参数,并分析了其检测原理与综合测试方法。通过对检测仪的伸缩式结构、光学系统、CCD选型和检测软件算法等部分进行设计,实现了一台检测仪能够对视场中心分辨力、亮度增益、视场亮度均匀性及视场亮度稳定性等多个性能参量的测试。试验结果表明,检测系统的测试误差在3%以内。     

基于灰度图差分梯度的雾化角测量方法北大核心CSCD

雾场边界及雾化角作为雾场的重要特性参数,主要通过图像法进行测量。在图像处理过程中,一般是将灰度图转化为二值化图像,然后依次针对二值化图像进行处理和计算。由于雾场的多相流特性,得到的二值化阈值和图像与实际雾场是否一致缺少评判依据。提出根据喷雾的灰度图像直接处理,得到掩模板并作用于灰度图像,采用图像形态学和迭代方法,计算灰度图像的梯度值。通过得到梯度值最大时的灰度图像,计算雾场边界和雾化角。实验表明,该方法提供了一种雾场边界的数值判断依据,通过梯度最大值判断并提取雾场边界,从而通过程序自动实现雾场边界提取与雾化角拟合测量。     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

Particle Image Velocimetry Applied to a Spray Jet

Experiments are described in which particle image velocimetry (PIV) is applied to the measurement of liquid droplets in a spray jet. The two velocity components in planes formed by the light sheet originating from a double-pulsed ruby laser are determined. The PIV records are evaluated with the method of Young's fringes. It is shown that this procedure allows the simultaneous measurement of the droplet size within a certain size range.     

Simultaneous Measurement of Droplet Size and Three-Components of Velocity in Spray

The combination of the optical diagnostics and image processing technique has produced various methods of practical measurement in engineering. The measurement of size and velocity of droplets in fuel spray is one typical example. In general, the spray is a complicated and three-dimensional two-phase flow; therefore multi-dimensional field measurement of the spray field is indispensable. In the present paper, a technique of simultaneous measurement of droplet size and three-components of velocity is proposed and applied to spray issuing from the swirl nozzle as a practical application. The focused image of glare points is captured by a stereoscopic arrangement, and droplet size and the three-components of velocity are evaluated from the doublet image. Fundamental optical arrangements to capture the image of the glare points with a stereo view are established, and the feasibility and the accuracy of the technique are confirmed. © 2004 The Optical Society of Japan     

Interferometric technique for measurement of droplet diameter

The paper considers the optical contact-free method of droplet diameter sizing in the flow cross-section utilizing light interference on a droplet. Distribution of light scattered by a particle was analyzed for different configurations of the measurement system using the Mie theory and approximation of geometrical optics. Basic measurement errors and dynamic range were determined. Possibility of measurements with camera mounting at the angle of 90° to the plane of a laser sheet is shown; this simplifies setup calibration and evens characteristics over the image field. The procedure of measurement system calibration and a set of algorithms for data processing are suggested. The suggested approaches were applied for measurement of characteristics of the gas-droplet jet.     

Optical diagnostics and direct injection of liquid fuel sprays

The research described here addresses the problem of a paucity of high quality data on the full field structure of high pressure liquid fuel sprays for gasoline direct injection, GDI, engines. The paper describes the application of phase Doppler anemometry, PDA, and single-shot laser sheet Mie imaging to the study of GDI sprays and discusses the methodologies adopted for the experimental systems and the optimisation of the techniques. Experimental data is presented which defines the spray structure in terms of PDA vector and scalar fields and single-shot CCD digital images. The work demonstrates the essential complementary nature of the single point and planar optical diagnostics for spray studies.     

一种基于投影原理的多弹孔识别方法

在基于图像识别的立靶密集度测试系统中,为了识别连发射击后的弹孔位置,提出了一种基于投影原理的多个弹孔识别方法。采用投影原理的矩形分割法将含有弹孔的图像分割成若干个区域,再用基于区域填充的十字模板法识别出弹孔并计算弹孔中心位置。给出了识别算法和计算公式。实弹射击实验结果表明,该方法能够有效地计算出连发射击后的弹孔着靶坐标,测量误差不大于1.5 mm。     

零锁区激光陀螺空间异面孔系投影角测量误差分析

针对异面腔零锁区激光陀螺深小孔系测量中准确性和稳定性差的问题,分析了异面腔零锁区激光陀螺深小孔测量中误差产生的原因。建立了倾角误差对空间异面孔系投影角的影响方程,发现空间异面孔系的倾角变化会改变投影角,当倾角为16时,倾角误差会以30%的分量加权到投影角误差中,并采用UG软件进行了仿真验证。采用最小二乘拟合的方法分析了影像测量仪的采点误差对角度的影响,发现了增加测量点数由2点增加到10点,超大采点误差的影响会减少至原来的50%。该方法增加了零锁区激光陀螺测量的稳定性。