LCoS背投光学引擎中变焦投影物镜设计

设计出变焦投影物镜，能满足相同光学引擎、相同屏幕位置下不同屏幕尺寸的需要。考虑到所设计的系统为大相对孔径、中等视场和小变焦比，从变焦理论出发，采用正组补偿的机械补偿法，对变倍组进行合理的倍率选段，求出了高斯解；然后分组元选用合理的初始结构，利用ZEMAX光学设计软件进行优化设计，解决了变焦系统畸变难以控制的问题，并使用调制传递函数对整个系统进行了综合评价。设计结果表明：该变焦投影物镜系统的光学性能和成像质量均满足设计指标要求，能应用于101.6～177.8cm的大屏幕电视。     

应用于激光扫描投影仪器的动态聚焦技术研究

为了实现激光投影仪器或系统的自动聚焦，研究搭建了激光动态聚焦系统。该系统可依据背向反射光强信号的变化调节聚焦系统的镜组间距，使激光扫描投影系统能够在不同距离的投影面上聚焦出最小光斑，从而提高系统的定位精度。根据激光动态自聚焦系统的原理，设计了光学杠杆型和反远距型2种动态自聚焦方案，并推导出相应的数学模型；利用ZEMAX光学设计软件进行仿真实验，通过比较得出响应更加灵敏、结构更加合理的自聚焦系统；搭建新型自聚焦激光扫描投影系统对动态自聚焦性能进行了验证。实验结果表明:反远距型动态自聚焦系统更加合理，在4.5 m处的投影面上，汇聚光斑直径最优可达0.2 mm，可使激光扫描投影仪在进行辅助装配时的定位准确度提高至0.1 mm，能够达到先进制造装配工程中零部件的精准定位要求。     

微型投影机光学引擎的研究

设计了一种针对个人用户使用的微型投影机光学引擎,系统为单片式数字光线处理器结构,采用红绿蓝三色大功率高亮度发光二极管作为光源,使用X棱镜作为合色元件,从而实现38.1～50.8 cm的彩色投影显示.对设计结果进行理论分析后可知,设计结果满足投影显示对颜色的要求,光学引擎的理论效率为16.1%.同时利用Light Tools仿真软件对系统进行建模分析,300万条光线追迹仿真的结果表明,光学引擎的效率为14.6%,与理论分析结果基本符合,屏幕上光通量为22.8 lm,其美国国家标准协会规定的九点照度均匀性达到91.55%和-93.36%,满足设计要求.     

数字光处理背投电视色度学特性的研究

以色度学的基本理论为基础,结合数字光处理光学引擎的工作原理,探讨了单片式数字光处理光学引擎的彩色显示原理和色温调节原理.提出了单片式数字光处理光学引擎色度学特性的理论计算公式,并利用该公式对夏新DL52HWT型投影电视光学引擎的显示三原色色度坐标、白场平衡的色度坐标和相关色温以及颜色复现误差等色度学特性进行了计算和分析,并对理论计算公式进行了验证.     

白光LED光学仿真中的相关色温计算

光学仿真是白光LED照明设计中的一个重要方法,但色度分布的光学仿真中计算量太过庞大,以致在一般计算条件下无法得到可靠的仿真结果。为解决这一问题,本文利用色度转换关系和逐点法计算色温,引入数值拟合和像素合成两种处理方法,有效降低了光学仿真结果的涨落。通过对处理结果和实验结果在照度和相关色温两方面的对比,两种处理方法的有效性得到证明,大幅提升了基于色度配光的光学仿真计算效率。     

DMD微投影显示的LED光学引擎设计

提出了基于矩形CPC的微投影显示匀光方法,设计了由LED、CPC、矩形复眼透镜及微显示芯片DMD构成的光学引擎。利用基于蒙特卡罗法的光线追迹软件分析了圆形CPC和矩形CPC对微投影显示匀光效果、光能利用率的影响。实验结果表明基于矩形CPC的光学引擎相对于基于圆形CPC的光学引擎有如下优点:体积小,光学扩展量小,照度均匀性高达到92%以上,能量利用率高达到43%以上,满足微显示芯片DMD的要求。     

基于LCoS拼接技术的动态星模拟器光学引擎的优化设计

为了降低基于硅基液晶拼接的动态星模拟器背景杂散光,对传统的光学引擎进行优化,提出一种多偏振分光棱镜组合方式,并对其光机结构进行设计.阐述了光学引擎照明系统的设计方案,讨论了降低视场角、增强均匀性的方法.通过Tracepro对照明光学系统进行仿真,对照明光源设计方案的可行性进行了验证.实验结果表明:优化后的动态星模拟器杂散光辐照度降低了2.93倍.优化后的光学引擎有效地抑制了背景杂散光,并且增强了两片反射式硅基液晶对比度的一致性.     

多色分图层激光扫描自聚焦投影技术

为了突破常规激光投影仪由于单一波长的局限性造成应用场景的限制,同时实现对不同零件、不同材料、不同装配工艺的分图层投影,设计并搭建了多色分图层激光扫描自聚焦投影系统。系统采用2种波长的激光作为光源,根据二向色镜的位置不同,提出了多色共光轴和分光路2种激光扫描自聚焦投影方案,并推导了相应的光学系统数学模型。通过系统的自聚焦功能调节镜组间距,均可以实现在不同距离的投影面上聚焦出不同颜色的最小光斑。利用ZEMAX光学设计软件对2种投影光学系统进行仿真,并从系统可靠性和投影效果上对2种系统进行比较分析。实验结果表明：在3 m处的投影面上,共光轴系统各种波长的光斑直径均在0.8 mm以内,且光斑大小均匀,可以实现多色分图层的扫描自聚焦投影功能。     

基于近焦点非球面透镜的LED均匀照明设计

依据几何光学和非成像光学理论,提出了一种基于大尺寸近焦点非球面透镜的大功率LED均匀光源设计方法。在该方法中,首先根据选定参数的LED通过几何光学理论初步设计非球面透镜参数,然后在ZEMAX软件中对非球面透镜参数进行基于评价函数的优化,得到焦距76.79 mm、直径为200 mm的非球面透镜。将非球面透镜导入TRACEPRO软件建模并进行光线追迹仿真,根据仿真结果获得最优透镜参数进行加工和下一步实验。实验结果表明:均匀照明系统可以在60 cm处实现发散角±8.53°的均匀照明,光斑均匀性达到95.82%。     

基于科赫曲线分形结构太赫兹带通滤波器

太赫兹滤波器是太赫兹通信、太赫兹成像和太赫兹检测等太赫兹应用系统中不可或缺的功能器件。按照不同的分类方式,滤波器有不同的种类,常见的按照选频功能可分为高通滤波器、低通滤波器、带阻滤波器和带通滤波器。为了实现在太赫兹波段的滤波效果,世界各地的研究人员利用不同的结构、材料和控制方式实现了功能各异的太赫兹滤波器,但是考虑到设计的器件要应用到太赫兹系统中,成本低廉、结构简单、性能优越的太赫兹滤波器一直是研究人员的追求。分形概念自提出以来在很多研究领域都有了快速发展,但是在太赫兹波段的应用还不是很常见,特别是应用于太赫兹功能器件的设计。引入分形中科赫曲线的概念设计并制备了一种新型的太赫兹带通滤波器,该滤波器是在金属薄膜上刻蚀出科赫曲线分形结构,当太赫兹波垂直入射到该滤波器时候实现了在太赫兹波段的窄带滤波。在滤波器的设计过程中,追求理论与实验相结合,首先在电磁仿真软件中建立科赫曲线分形结构滤波器模型进行计算,探究分形结构应用于太赫兹波段进行滤波的可行性,在进行多次计算之后得到优化后的尺寸和结构,然后根据优化后的尺寸加工出科赫曲线分形结构太赫兹滤波器样品,并且将样品放在太赫兹时域光谱系统中进行实验测量,得到实验数据后与仿真结果进行比较。在仿真中利用了时域有限差分法模拟科赫曲线分形结构太赫兹带通滤波器的传输特性,优化后的仿真结果表明:滤波器的谐振频率为0.715 THz,透射系数能够达到0.92,-3 dB带宽为21.9 GHz,将仿真得到的散射参数进行S参数反演得到了太赫兹滤波器样品的电磁参数,这在理论上分析了太赫兹波在谐振点处产生透射增强的原因。利用飞秒激光微加工系统制备了尺寸优化后的科赫曲线分形结构太赫兹带通滤波器样品,然后使用太赫兹时域光谱系统对样品的传输特性进行测试,对实验得到的时域数据进行快速傅里叶变换之后得到频域数据,再把频域数据进行归一化处理后与之前的电磁仿真结果进行对比,发现实验测得的结果与电磁软件仿真得到的结果较为吻合。     

Optical characterization of methanol compression-ignition combustion in a heavy-duty engine

In the search for renewable fuels, there are very few candidates as compelling as methanol. It can be derived from refuse material and industrial waste, while the infrastructure exists worldwide to support broad and fast adoption, potentially even as a “drop-in” fuel for existing vehicles with only minor modifications. The most efficient engines currently available are compression-ignition engines, however they often come with high emissions or compromises like the soot-NO_x trade-off. Methanol however, is a low sooting fuel that can potentially be used in such engines despite its high resistance to auto-ignition and reduce emissions while maintaining high engine efficiency. Due to the auto-ignition resistance, few studies of methanol compression-ignition exist and even fewer are conducted in an optically accessible engine. Here, two cases of premixed combustion and two of spray-driven combustion of methanol are studied in a Heavy-Duty optically accessible engine. Ignition and combustion propagation are characterized with a combination of time-resolved natural flame luminosity measurements and single-shot, acetone fuel-tracer, laser induced fluorescence. Additionally, Mie-scattering is used to identify the interaction between liquid spray and ignition sites in spray-driven methanol combustion. Results show that methanol combusts drastically different compared to conventional fuels, especially in spray-driven combustion. The evaporative cooling effect of methanol appears to play a major role in the auto-ignition characteristics of the delivered fuel. Ignition sites appear right at the end of injection when the evaporative cooling effect is withdrawn or at liquid length oscillations where, again the effect is momentarily retracted. To the authors’ knowledge, this has not been documented before.     

A comparative study on partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI) in an optical engine

Partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI) are two new combustion modes in compression-ignition (CI) engines. However, the detailed in-cylinder ignition and flame development process in these two CI modes were not clearly understood. In the present study, firstly, the fuel stratification, ignition and flame development in PPC and RCCI were comparatively studied on a light-duty optical engine using multiple optical diagnostic techniques. The overall fuel reactivity (PRF number) and concentration (fuel-air equivalence ratio) were kept at 70 and 0.77 for both modes, respectively. Iso-octane and n-heptane were separately used in the port-injection (PI) and direct-injection (DI) for RCCI, while PRF70 fuel was introduced through direct-injection (DI) for PPC. The DI timing for both modes was fixed at –25°CA ATDC. Secondly, the combustion characteristics of PPC and RCCI with more premixed charge were explored by increasing the PI mass fraction for RCCI and using the split DI strategy for PPC. In the first part, results show that RCCI has shorter ignition delay than PPC due to the fuel reactivity stratification. The natural flame luminosity, formaldehyde and OH PLIF images prove that the flame front propagation in the early stage of PPC can be seen, while there is no distinct flame front propagation in RCCI. In the second part, the higher premixed ratio results in more auto-ignition sites and faster combustion rate for PPC. However, the higher premixed ratio reduces the combustion rate in RCCI mode and the flame front propagation can be clearly seen, the flame speed of which is similar to that in spark ignition engines but lower than that in PPC. It can be concluded that the ratio of flame front propagation and auto-ignition in RCCI and PPC can be modulated by the control over the fuel stratification degree through different fuel-injection strategies.     

6106柴油机性能研究及优化

本文利用内燃机工作过程数值模拟软件GT-Power,对6106柴油机工作过程进行了数值模拟计算.通过计算,分析了供油提前角、配气相位等参数对柴油机性能的影响,并将计算结果与实验值进行了比较,验证了计算的准确性.优化后的结果为柴油机的优化设计提供理论依据.     

Advanced gasoline engine development using optical diagnostics and numerical modeling

Twenty years ago, homogeneous-charge spark-ignition gasoline engines (using carburetion, throttle-body-, or port-fuel-injection) were the dominant automotive engines. Advanced automotive engine development remained largely empirical, and stratified-charge direct-injection gasoline-engine production was blocked by lack of robustness in its combustion process [W.G. Agnew, Proc. Combust. Inst. 20 (1984) 1-17]. Today, a wide range of direct-injection gasoline engines are in (or near) production, and combustion science is playing a direct role in advanced gasoline-engine development through the simultaneous application of advanced optical diagnostics, three-dimensional computational fluid dynamics (CFD) modeling, and traditional combustion diagnostics. This paper discusses the use of optical diagnostics and CFD in five gasoline-engine combustion systems: homogeneous spark-ignition port-fuel-injection (PFI), homogeneous spark-ignition direct-injection (DI), stratified wall-guided spark-ignition direct-injection (WG-SIDI), stratified spray-guided spark-ignition direct-injection (SG-SIDI), and homogeneous-charge compression-ignition (HCCI). The emphasis is on WG-SIDI, SG-SIDI, and HCCI engines. Key in-cylinder physical processes (e.g., sprays and vaporization, turbulent fuel-air mixing, wall wetting, ignition and early flame development, turbulent partially premixed flame propagation, and emissions formation) can be visualized, quantified, and optimized through optical engine experiments and CFD-based engine modeling. Outstanding issues for stratified engines include reducing piston wall-wetting, pool fires and smoke in WG-SIDI engines, eliminating intermittent misfires in SG-SIDI engines, and optimizing lean NO_x after-treatment systems. HCCI engines require better control of combustion timing and heat-release rate over wide speed/load operating ranges, smooth transitions between operating modes, and individual cylinder sensors and controls. Future directions in optical diagnostics and modeling are suggested to improve our fundamental understanding of important in-cylinder processes and to enhance CFD modeling capabilities.     

Impact of coolant temperature on piston wall-wetting and smoke generation in a stratified-charge DISI engine operated on E30 fuel

A late-injection strategy is typically adopted in stratified-charge direct injection spark ignition (DISI) engines to improve combustion stability for lean operation, but this may induce wall wetting on the piston surface and result in high soot emissions. E30 fuel, i.e., gasoline with 30% ethanol, is a potential alternative fuel that can offer a high Research Octane Number. However, the relatively high ethanol content increases the heat of vaporization, potentially exacerbating wall-wetting issues in DISI engines. In this study, the Refractive Index Matching (RIM) technique is used to measure fuel wall films in the piston bowl. The RIM implementation uses a novel LED illumination, integrated in the piston assembly and providing side illumination of the piston-bowl window. This RIM diagnostics in combination with high-speed imaging was used to investigate the impact of coolant temperature on the characteristics of wall wetting and combustion in an optical DISI engine fueled with E30. The experiments reveal that the smoke emissions increase drastically from 0.068 FSN to 1.14 FSN when the coolant temperature is reduced from 90 °C to 45 °C. Consistent with this finding, natural flame luminosity imaging reveals elevated soot incandescence with a reduction of the coolant temperature, indicative of pool fires. The RIM diagnostics show that a lower coolant temperature also leads to increased fuel film thickness, area, and volume, explaining the onset of pool fires and smoke.     

变角度色度和LED单管光色多用校准装置研制

采用二维自动转动控制结合伺服电机、传感器及测量软件等设计了一种可实现光源和物体的表面空间变角度光度、色度等参数测量的多用校准装置,解决了目前LED单管、显示器和标准色板等三类产品光度色度参数需使用独立测量装置的问题。结果显示可完成LED单管总光通量、CIE条件A/B场平均发光强度、等光强/照度曲线、小尺寸显示器光度色度和物体表面变角度色度等参数的测量。平均发光强度、总光通量、Y值和色品坐标与标准值偏差分别为:-1.8%、1.5%、0.9和0.005,该装置测量精度高、功能切换方便、自动化水平高、操作简单,达到设计要求。     

In-cylinder gas temperature and water concentration measurements in HCCI engines using a multiplexed-wavelength diode-laser system: Sensor development and initial demonstration

A wavelength-multiplexed, fiber-optic-based, line-of-sight, diode-laser absorption sensor is developed for crank-angle-resolved measurements of temperature and water concentration in a homogeneous-charge-compression-ignition (HCCI) engine. An initial demonstration of its use on two optical HCCI engines at Sandia National Laboratories is reported. The measurements encompassed both motored- and fired-engine operation for temperatures between 300 and 1700 K and pressures between 1 and 55 bar. A spectroscopic line selection process identifies the most appropriate water absorption linepair for thermometry under these conditions. Key solutions to suppress crank-angle-dependent noise in the transmitted laser signals are reported, including careful spectroscopic design and optical engineering to accommodate beam-steering, engine vibration and polarization-related interference. Data obtained through this sensor can provide critical engine characteristics such as combustion efficiency, peak combustion temperature, and autoignition temperature. The flexibility of the wavelength-multiplexed architecture allows the straightforward addition of other wavelengths to potentially enable the simultaneous measurement of other important engine parameters such as temperature non-uniformity, and fuel, CO, and CO₂ concentrations.     

斜爆轰发动机流动机理分析

为了研究高Mach数超燃冲压发动机和斜爆轰发动机的内流场燃烧流动机理，首先用CJ爆轰理论对超燃冲压发动机的内流场特性进行了理论分析，给出了燃烧室流场的气动规律，理论分析结果与现有实验结果吻合得非常好.其次，根据理论分析结果，提出了高Mach数超燃冲压发动机和斜爆轰发动机的气动设计原则.最后，根据提出的气动设计原则，设计了高Mach数斜爆轰发动机，飞行Mach数为9，对斜激波诱导燃烧机理开展了二维数值模拟研究.数值模拟结果表明，在高Mach数下，斜爆轰发动机燃烧室内可以得到稳定的燃烧流场.