锆粉尘云的火焰传播特性

使用高速摄影、超细热电偶和纹影技术,对方形开口管道中锆粉尘云火焰传播特性进行了实验研究.锆粉尘通过压缩空气喷散到管道中形成粉尘云,随后,锆粉尘云被电火花点燃.实验结果表明,低质量浓度下,火焰传播速度和温度随质量浓度增加而增加.当粉尘云质量浓度为0.627 kg/m3时,火焰传播速度和温度达到最大值,分别为30.41 m/s和1716 K,其后随着质量浓度的继续增加,火焰传播速度和温度开始略微下降.锆粉尘云中粒子与空气形成气-固表面燃烧体系,一些粒子在燃烧结束前发生微爆.预热区厚度在0.39～2.52 cm,随粉尘云质量浓度的增加先减小后增加.     

PMMA微粒子云中传播火焰的基本结构

以揭示可燃粉尘云中传播火焰的基本结构和燃烧反应区的反应特性为目的，用CCD和高速摄像仪拍摄了PMMA粉尘云中传播火焰的自发光和和粒子的激光散射图片，结合离子探针和微细热电偶测试技术，根据实测结果分析了有机可燃物PMMA粉尘云中传播火焰的基本结构；揭示了燃烧反应区的反应特性、反应强度分布规律和温度分布规律。     

玉米粉火焰在开口垂直管道中的传播

以对粉尘云状态参数的定量测定为基础,对玉米粉尘火焰在开口垂直管道中向上传播的过程进行了实验研究.在情形A中,火焰从管道的封闭端向开口端传播,在情形B中,从开口端向封闭端传播.实验中,观察到两种粉尘火焰,即湍流火焰和层流火焰,火焰形态转变对应的点火延迟时间约等于1.1 s,即粉尘云湍流运动强度为10cm/s.情形A中,层流火焰的传播出现周期性振荡现象,湍流火焰在传播过程中不断加速;情形B中,两种火焰都匀速传播,湍流火焰传播速度明显大于层流火焰.在所考察的实验条件下,粉尘浓度对于玉米粉尘火焰传播速度的影响不大.     

低热值气体发动机涡团与火焰面相互作用

基于大涡模拟方法对一台燃用低热值气体燃料的发动机缸内湍流涡团与火焰相互作用过程开展了模拟,分析了缸内急燃期火焰传播过程中火焰前锋面上湍流涡核的分布特征,研究湍流涡团与火焰面的相互作用机理,并研究了涡对结构对火焰面传播的影响.结果表明:急燃期燃烧过程中,缸内背景湍流和火焰面相互作用,促使高强度涡核分布在火焰前锋面上,而涡核增大火焰面褶皱程度,火焰面面积增加,有助于更多高强度火核的产生;未燃区涡对的两个涡团相互逆向旋转导致火焰面受到局部的卷吸或者拉伸等作用,是火焰面出现明显皱褶的主要原因.     

高温高压下二甲醚—空气预混层流燃烧特性研究

在定容燃烧弹内研究了初始压力为0.5 MPa时,不同初始温度和燃空当量比下二甲醚-空气混合气预混层流火焰的层流燃烧速率和马克斯坦长度,分析了火焰拉伸对火焰传播速率的影响.基于容弹燃烧的双区模型计算了预混层流燃烧的燃烧特性参数.结果表明:随着初始温度的增加,二甲醚-空气预混合气的无拉伸火焰传播速率和无拉伸层流燃烧率增加;对于给定的初始温度,在化学当量比偏浓混合气一侧存在一个层流燃烧速度的峰值;随初始温度和当最比增加,马克斯坦长度值减小,火焰前锋面的不稳定性增加;最大燃烧压力随初始温度的增加而下降,压力升高率随初始温度的增加而降低.     

浸没难挥发性可燃液体的多孔介质表面火焰传播特性

实验研究了浸没难挥发性可燃液体的多孔介质表面火焰的传播特性.丁醇和石英砂分别作为浸入的难挥发性可燃液体和多孔介质.研究结果表明:液面高度和介质粒径对于火焰传播过程中火焰的结构、火焰传播速度以及砂层的温度分布都有着显著的影响;火焰在传播过程中,火焰前锋前面的砂表面预热区内存在一气化可燃物析出区域(约为5.6,mm),其对火焰的传播起着重要作用.     

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.     

天然气直喷燃烧的可视化研究

利用高速摄影装置开展了天然气直喷燃烧的可视化研究。研究结果表明:缸内形成的分层充量分布与喷射方式有关,双点平行喷射和单点喷射将比双点对向喷射形成的充量分层强。双点平行喷射和单点喷射时火焰将向燃料喷流的下流区发展,而双点对向喷射时火焰显示出由燃烧室中心向外围方向发展的特征。天然气直喷燃烧呈现出湍流燃烧特征的皱褶火焰前锋面。通过优化喷射正时形成的可燃分层充量可实现直喷天然气超稀燃烧。     

基于谱色测温的航空煤油池火焰温度分布实验研究

火焰温度是表征燃料燃烧特性的基本热力参数.根据谱色测温的线性发射率假设模型,结合三基色的光谱响应函数,对直径分别为0.15、0.20、0.30和0.60 m航空煤油池火焰温度分布进行实验研究,给出了火焰温度在轴向垂直高度上的连续分布规律,对比分析了不同直径油池火焰平均温度.结果表明,燃料表面区域温度相对较低,在连续火焰区上部,随着高度的增加火焰温度上升,在火焰上部的间歇区,火焰温度在轴向高度上的变化比较紊乱,弥散程度较大;不同直径油池火焰平均温度分布在1 180～1 220 K,随着油池直径的增大,火焰平均温度有所上升.     

缸内直喷CNG发动机喷射方式对火焰传播特性及性能的影响

火焰传播是点燃式发动机的主要燃烧方式,为了有效控制缸内直喷CNG发动机更稳定的稀薄燃烧过程,以实现高效率低排放,利用试验用单缸光学发动机,采用双喷射器缸内直喷CNG方式,在双火花塞点火的条件下,分析研究了不同喷射方式对火焰形成及传播特性以及发动机性能的影响.结果表明,双点点火时,缸内气流对首先形成的火焰具有"牵引"作用,而两个火焰由于形成时刻不同传播方式就有区别,且两个火焰之间具有"挤压或推动"作用,由此影响整体火焰传播速度;缸内火花塞附近混合气浓度越浓或不均匀性越大,循环波动越小,燃烧更稳定,但随混合气浓度分布不均匀性的增加,NOx排放也增加,表明基于混合气浓度不均匀性分布特性的燃烧过程中,NOx的生成机理不仅与高温富氧条件有关,而且还与浓度场分布特性有直接的关系.     

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.     

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。     

Contents in Volume 23,2014

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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.