SOM‐based projection module for mobile displays

Abstract— The development of a compact, efficient VGA projection module to be embedded in mobile devices is reported. The design incorporates laser/laser diode (LD) light sources, Schlieren optics, and a one‐dimensional diffractive spatial optical modulator (SOM). During development, the optical parameters were determined and the relationships between the parameters to optimize the optical specifications were derived. The resulting optimized specifications enable us to manufacture two types of optical modu les as compact as 13 cc and with as little as 10% speckle contrast ratio.     

An experimental analysis on the evolution of the transient tip penetration in reacting Diesel sprays

Schlieren imaging has helped deeply characterize the behavior of Diesel spray when injected into an oxygen-free ambient. However, when considering the transient penetration of the reacting spray after autoignition, i.e. the Diesel flame, few studies have been found in literature. Differences among optical setups as well as among experimental conditions have not allowed clear conclusions to be drawn on this issue. Furthermore, soot radiation may have a strong effect on the image quality, which cannot be neglected.     

Experimental study and three-dimensional simulation of premixed hydrogen/air flame propagation in a closed duct

An experimental and numerical study of premixed hydrogen/air flame propagation in a closed duct is presented. High-speed schlieren photography is used in the experiment to record the changes in flame shape and location. The pressure transient during the combustion is measured using a pressure transducer. A dynamic thickened flame model is applied to model the premixed combustion in the numerical simulation. The four stages of the flame dynamics observed in the experiment are well reproduced in the numerical simulation. The oscillations of the flame speed and pressure growth, induced by the pressure wave, indicate that the pressure wave plays an important role in the combustion dynamics. The predicted pressure dynamics in the numerical simulation is also in good agreement with that in the experiment. The close correspondence between the numerical simulation and experiment demonstrate that the TF approach is quite reliable for the study of premixed hydrogen/air flame propagation in the closed duct. It is shown that the flame wrinkling is important for the flame dynamics at the later stages.     

CO2-乙醇体系中界面对流的混合格子Boltzmann方法三维模拟及实验验证（英文）

By using a hybrid lattice-Boltzmann–finite-difference method (hybrid LBM–FDM method), three-dimensional simulations of solutal interfacial convection were conducted for the process of CO2 absorption into ethanol. A self-renewal interface model is adopted as an interfacial perturbation model. The simulation results revealed some three-dimensional features of the induced interfacial convection, such as the development of diverging cellular flow and Rayleigh plume-like convection in liquid phase. The concentration distribution of the simulation result is validated and found to be in wel agreement with the Schlieren visualization results qualitatively. Addi-tionally, the mass transfer enhancements by interfacial convection were investigated via both simulation and experiment for the absorption process, and the mass transfer is shown to be enhanced by the interfacial convec-tion by about two-fold comparing with that by diffusion.     

Experimental and numerical study on premixed hydrogen/air flame propagation in a horizontal rectangular closed duct

Hydrogen is a promising energy in the future, and it is desirable to characterize the combustion behavior of its blends with air. The premixed hydrogen/air flame microstructure and propagation in a horizontal rectangular closed duct were recorded using high-speed video and Schlieren device. Numerical simulation was also performed on Fluent CFD code to compare with the experimental result. A tulip flame is formed during the flame propagating, and then the tulip flame formation mechanism was proposed based on the analysis. The induced reverse flow and vortex motion were observed both in experiment and simulation. The interactions among the flame, reverse flow and vortices in the burned gas change the flame shape and ultimately it develops into a tulip flame. During the formation of the tulip flame, the tulip cusp slows down and stops moving after its slightly forward moving, and then, it starts to move backward and keeps on a longer time, after that, it moves forward again. The structure of the tulip flame is becoming less stable with its length decreasing in flame propagation direction. The flame thickness increases gradually which is due to turbulence combustion.     

Design rules for Background Oriented Schlieren experiments with least-squares based displacement calculation

Background Oriented Schlieren (BOS) is a non-intrusive optical method used to visualize density variations in fluids. A camera is used to measure the distortion of a background image displaying a random pattern due to the refraction of the light induced by the local gradients in the refractive index of the under study. In contrast to conventional schlieren, for which direct observation is possible, the images obtained with the BOS technique have to be processed. In this contribution, a computationally affordable approach based on linear least-squares minimization and adapted from optical flow techniques is presented in detail and tested in the context of BOS with the Matlab GUI application comBOS. A series of synthetic images are first analyzed to devise design rules for the definition of an optimal random Gaussian dot background pattern. Tests are performed for comBOS, the commercial BOS module included in DaVis 10, and the free PIV tool PIVlab. It is found that the diameter of the dot images on the camera sensor should be at least 3 pixels, but can be larger without affecting the accuracy of the measurement with comBOS and DaVis 10, while PIVlab severely degrades the quality of the results for dots larger than 5 pixels. The contrast and the density of dots must also be sufficient such that a minimum of 75 % of the surface of the background is shaded. If these conditions are met, the maximum systematic error in the measured distortions is 0.006 pixel for comBOS and 0.001 pixel with DaVis 10 when local gradients are small. Similar errors are found with PIVlab for dots smaller than 5 pixels in diameter, but they increase rapidly for larger dots. The random error is typically smaller than 0.004 pixel in optimal conditions, but it increases significantly for images affected by a random noise or local gradients of the distortion. Finally, it is concluded with a realistic test case that both comBOS and DaVis 10 are well suited to capture the main features of a complex compressible flow with Schlieren imaging. Thus, the main advantage of comBOS is its affordability and robustness for researchers and educators willing to implement BOS, for example in educational contexts.     

Experimental investigation of spherical-flame acceleration in lean hydrogen-air mixtures

Large-scale experiments examining spherical-flame acceleration in lean hydrogen-air mixtures were performed in a 64 m³ constant-pressure enclosure. Equivalence ratios ranging from 0.33 to 0.57 were examined using detailed front tracking for flame diameters up to 1.2 m through the use of a Background Oriented Schlieren (BOS) technique. From these measurements, the critical radii for onset of instability for these mixtures, on the order of 2–3 cm, were obtained. In addition, the laminar burning velocity and rate of flame acceleration as a function of radius were also measured.     

壁面碰撞对柴油油束扩展及着火特性的影响

本文介绍以一压力观察室研究壁面碰撞对柴油油束特性的影响,采用纹影摄影法及光导纤维技术确定油束的扩展过程、着火延迟及着火位置,并在柴油机工作条件下分析了壁面温度、壁面与油束相对位置及空气温度的影响。统计结果表明,在较高壁面温度时油束可以在壁表面首先着火;减小油束碰撞角度,增大壁面与油嘴的距离或提高空气温度可降低壁面对油束着火特性的影响。     

纹影干涉诊断等离子体弧

本文阐述了纹影干涉法诊断等离子体弧的基本原理和实验装置，建立了纹影干涉法诊断等离子体弧的数据处理方法。实验结果表明：这种诊断方法准确、实用，易于进行工作过程中的等离子体弧动态特性的研究．为探讨等离子体弧行为与加工质量间的内在联系，提供了一种最有效的方法．     

Dynamics of premixed hydrogen/air flame in a closed combustion vessel

The dynamics of a premixed hydrogen/air flame propagating in a closed vessel is investigated using high-speed schlieren cinematography, pressure measurement and numerical simulation. A dynamically thickened flame approach with a 19-step detailed chemistry is employed in the numerical simulation to model the premixed combustion. The schlieren photographs show that a remarkable distorted tulip flame is initiated after a classical tulip flame has been fully produced. A second distorted tulip flame is generated with a cascade of indentations created in succession before the vanishing of the first one. The flame dynamics observed in the experiments is well reproduced in the numerical simulation. The burnt region near the flame front is entirely dominated by a reverse flow during the formation of the distorted tulip flame. The distorted tulip flame can be formed in the absence of vortex motion. The pressure wave leads to periodic flame deceleration and plays an essential role in the distorted tulip formation. The numerical results corroborate the mechanism that the distorted tulip flame formation is a manifestation of Taylor instability.