运用激光层析观测预混火焰前锋

介绍了用激光层析探测燃烧场的原理及其装置和图像处理工具的开发过程.利用预混V形火焰进行了激光层析探测火焰前锋的实验,结果显示,该方法能够在入射光平面内清晰地分辨火焰皱褶在任一瞬间的几何形状.利用主动轮廓算法从数字化图像中准确提取了火焰前锋的轮廓线形,为火焰皱褶及其传播特性的量化分析打下了基础.     

以多尺度颜色小波纹理特征为基础的工业炉火焰图像分割研究

分割火焰图像最常用的方法是分类算法,而使用这种算法最大的缺陷在于当像素点数增高时,分割图像的耗时就越大。通过以火焰图像采集装置来采集研究样本,提出了一种可以加快分割速度的方法及运用多尺度颜色小波纹理特征为基础的工业炉火焰图像分割法,经过对图像特征矩阵进行压缩,采用分类算法获取压缩尺度火焰区域并检测其边缘;根据压缩尺度火焰边缘进一步检测其在原始尺度区域,构建边缘区域特征矩阵并进一步检测,从而得到原始尺度火焰区域图像的目的。     

基于图像亮度统计分析火焰高度特征

火焰高度是燃烧火焰的一个重要参数,它影响火焰的传播及辐射特性,而火焰高度特征包括平均火焰高度和脉动频率两个方面.基于Matlab视频图像分析,提出了通过统计火焰图像时间序列中各位置处出现亮点的概率和火焰中心线上的亮点个数,来提取火焰的平均高度和脉动频率的方法.开展了0.5 m×0.5 m、0.7 m×0.7 m和0.8 m×0.8 m三组方形油盘火试验,利用该方法获得了它们的平均火焰高度和脉动频率,并和Heskestad模型、Pagni模型、Bejan模型和Cetegen模型的理论预测值进行了对比,结果表明,该方法得出的平均火焰高度和火焰脉动频率均与理论预测值比较接近.     

圆周运动下移动火源扩散火焰的图像特性分析

为了预测和控制移动火源扩散火焰的燃烧,对火焰图像特性的影响因素和规律进行研究.通过高速摄像仪,实时记录移动火源扩散火焰在圆周运动下的形态特征,利用力场分析和MATLAB工具,得到火焰面积随火焰线速度的变化规律以及火焰倾角随火焰线速度的变化.研究发现,燃烧产生热量和气流散热两者综合地导致火焰面积随着线速度的递增而先增大后减小;随着火焰线速度的增大,刚开始火焰倾角升幅较快,后趋于平缓;火焰内外温差会影响浮升力的大小,进而影响燃烧的稳定性.     

电站锅炉火焰检测及燃烧诊断技术

电站锅炉的安全运行主要决定于燃烧的稳定性，实时探测燃烧火焰是否稳定，及时作出判断，对电站锅炉安全运行有着重要的实际意义。本文分析了炉膛火焰特征与火焰检测和燃烧诊断的关系，论述了火焰检测的基本原理和方法以及燃烧诊断理论和技术，并对目前火电厂燃煤锅炉应用的各种火焰检测器和燃烧诊断系统进行了分析比较，最后讨论了火焰检测及燃烧诊断技术的进一步研究方向。     

基于图像相关性提取的火焰振荡频率

振荡频率是燃烧火焰的一个重要基本参数,利用Matlab图像分析工具,分析了连续火焰图像序列的相关性,并对图像相关系数随时间的变化过程进行快速傅里叶变换,从而提取出火焰的振荡频率.采用该方法分析实验获得的0.7 m×0.7 m油盘火焰的视频图像,得出火焰的振荡频率为1.80 Hz,Pagni公式的理论预测值为1.71 Hz,两者比较接近.另外,研究发现同一图像序列中红、绿、蓝3个颜色分量的图像相关性系数差别较大,但它们的变化频率一致,表明采用该方法分析得到的振荡频率值不受颜色分量选择的影响.     

光学读出微悬臂梁阵列火焰检测系统

光学读出微悬臂梁对红外辐射具有很高的灵敏度与热响应速率,十分适用于火焰探测领域.当火焰所产生红外辐射入射到微悬臂梁阵列时,相应的微悬臂梁单元会发生形变,通过光学读出系统将这种变化成像在相机上,就能够获得火焰的图像信息.根据理论计算,微悬臂梁的像元尺寸为100μm×80μm时,热响应时间为20.5 ms.由于此系统不受可见光干扰,使用阈值法对图像进行处理后,能够得到清晰的火焰图像.实验表明:此系统可达到100帧/s的火焰图像处理速度,极大降低了火焰检测的响应时间,提高了火焰的检测速度.     

振荡燃烧火焰图像处理

应用图像FFT、本征正交分解(POD)和动力学模态分解(DMD)3种方法,对在振荡燃烧环境下的火焰图像进行分解,得到火焰脉动幅值、主频以及初始相位.其中通过图像FFT方法分析图像中每一个像素灰度值时间序列,对其进行傅里叶变换,然后得到整体火焰的振荡特性.而POD和DMD方法将每一张火焰图像视为一个样本数据,以向量的形式表达,通过线性代数和矩阵分析等理论对样本数据进行分解.DMD和图像FFT两种方法得到的火焰脉动幅值和主频基本一致,可以得到单一频率(基频和各谐频)脉动特征,而POD方法无法将各种振荡频率对应的脉动结构进行分离,得到总的脉动结构.结果表明上述3种方法均可以捕捉振荡燃烧环境下火焰的主要脉动特征.     

液体燃料扩散小火焰的实验研究

采用内径分别为1.0、0.6和0.4 mm的陶瓷管燃烧器,以液态乙醇为燃料,对其扩散小火焰特性进行实验研究.采用体视显微镜配合数字摄像头对火焰图像进行了可视化测量,得到了火焰图像的无量纲特征尺寸随Re变化关系.分别采用热电偶和红外热像仪对火焰温度及陶瓷管外表面温度场进行了测量,分析了火焰淬熄时的温度特性,并定性地分析了浮力对火焰的影响.     

W型火焰锅炉炉膛温度场的可视化试验研究

使用火焰辐射图像探测系统探测炉膛空间发射到镜头各像素的辐射能量,然后从能量传递和平衡的角度,由所得图像重建空间的温度场。在300MW机组W型火焰炉进行了炉膛二维断面温度场可视化重建试验。试验在炉膛壁面布置4个CCD火焰探测器,采用计算机图像采集处理技术获取炉膛火焰辐射图像,通过对火焰辐射图像的处理以厦相关算法,重建炉膛断面温度分布、可动态反映火焰断面温度水平、火焰中心的偏穆和火焰刷墙等燃烧异常工况。断面温度场可视化结果刷新一次的时间不超过5S,满足在线监测的要求。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Contents in Volume 23,2014

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汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.