环状侧电极火花塞头部导热特性研究

环状侧电极火花塞较之传统单侧电极具有良好的点火性能,但是其头部易积炭的缺点限制了在内燃机中的使用寿命。为此,采用有限元数值模拟方法,以F6TH型多向点火火花塞为原型,将其几何结构及边界条件合理简化后,建立此火花塞头部的二维非稳态导热数学模型,运用ANSYS软件进行了热荷加载及温度场数值模拟,得出了四种不同尺寸组合情况下火花塞头部温度场分布情况,分析了环状侧电极的宽度、中心电极芯部半径及中心电极帽部半径尺寸这三个关键结构参数的改变对温度分布的影响趋势。最后利用模拟分析结果结合此产品具体使用情况的反馈报告,进而为此问题的解决提供了可行性较强的定性方案和建议。所得结论对于火花塞的结构设计具有实用参考价值。     

侧插式等离子体点火特性数值模拟

以Fluent软件为计算平台,针对侧插式等离子体点火燃烧器内部三维湍流流场及点火特性进行数值模拟,计算了煤粉混合物在通过整个燃烧器时内部温度场、着火过程成分变化等。分析了在给定来流条件下,等离子体功率对燃烧器出口横截面、中心纵截面温度场局部及整体分布和燃烧器中心轴线上温度特性曲线的影响。分析了点火燃烧过程中CO2、CO、H2O和O2的质量浓度分布与温度分布的关系。     

中心轴插式等离子体点火特性数值模拟

以Fluent软件为计算平台,针对中心轴插式等离子体点火燃烧器内部三维湍流流场及点火特性进行数值模拟,计算煤粉混合物在通过整个燃烧器时内部温度场、着火过程成分变化和煤粉的燃尽率等,分析其点火燃烧器内部的燃烧特征.分析了在给定来流条件下,不同等离子体喷枪功率下,点火煤粉燃烧器内中心截面温度分布;分析了点火煤粉燃烧器内CO、O2和CO2的质量浓度分布与温度分布的关系.     

双点火间隙等离子流火花塞的设计与探讨

通过分析火花塞等离子体产生机理及点火过程中等离子流能量的变化,设计出双点火间隙电极结构的等离子流火花塞及其点火电路,该火花塞工作时两个间隙同时点火形成双火核,点火能量增大.放电测量结果为,当特征长度L+=10mm,电极间隙h=1.0mm时,点火电压为19000V,最大峰值电流为200A,点火能量为103mJ.     

火花塞及其使用

火花塞是发动机点火系统中的一个重要电器部件,广泛用于汽车、拖拉机、摩托车、操舟机以及各种类型的小型汽油机上。它的作用是将高压线圈感应出来的高压电,经过高压导线的传导,在火花塞的中心电极和侧电极之间,产生强烈的点火火花,从而点燃燃烧室内的燃料—空气混合气,推动活     

六角形玻璃电熔窑内部流动与传热特性数值模拟

采用内热源结合固定电极壁温的方法替代实际电熔窑交变电场焦耳热的产生,通过数值求解基于雷诺时均的三维定常黏性N-S方程及能量方程,对某实际运行的六角形玻璃电熔窑内部的流场、温度场进行了数值模拟研究。通过与物理模拟试验结果相比对,验证了提出的内热源结合固定电极壁温方法的正确性,运用该方法对玻璃电熔窑内温度场及流场开展模拟研究,获得了其内部温度分布特点、涡系结构及流场细节,为玻璃电熔窑的设计及优化提供了一定参考。     

对置活塞二冲程汽油机多点点火燃烧特性研究

由于取消了气缸盖,对置活塞二冲程(OP2S)汽油机的火花塞只能布置于气缸侧壁。因此在单火花塞点火时,缸内火焰传播不对称,导致OP2S汽油机具有较明显的爆震倾向。为了有效地抑制爆震的发生,利用三维CFD软件对OP2S直喷汽油机在不同火花塞数目下缸内的燃烧过程进行了数值仿真,并结合试验研究了火花塞数目对混合气燃烧特性的影响,分析了不同火花塞数目对缸内燃烧压力、燃烧持续期及燃烧放热率的影响规律。研究结果表明,增加火花塞数量可以有效改善缸内的燃烧情况,而对侧布置双火花塞的布置形式为最佳方案。     

Helmholtz型无阀自激脉动燃烧器点火过程数值模拟研究

本文利用FLUENT 15. 0软件,在无特殊周期性边界条件的影响下,采用标准的k-epsilon模型成功模拟了Helmholtz型无阀自激脉动燃烧器的点火过程。模拟结果和前期实验现象结果吻合良好,为点火过程的分析提供了更多的数据支持。根据数值模拟结果探讨了Helmholtz型无阀自激脉动燃烧器整个点火过程中,燃烧器中压力和气体流速的变化和分布情况。分析了前期爆燃过程中脉动燃烧器中温度场的变化情况及回流现象。进一步佐证了爆燃能量集聚和烟气回流是脉动燃烧器成功点火的重要原因。     

浅析1E40F型汽油机故障的检查

汽油机在使用中,常出现起动困难故障,其主要原因有点火系统、供油系统、密封性能三方面的因素。检查时,应从简到繁,由表及里逐步深入地进行。 1 检查点火系统故障 1.1 检查火花塞将火花塞从气缸盖上拧下,接上高压线,使其螺纹部分紧贴机体,用手快速转动起动轮,观察火花塞电极间跳火情况。 a.若电极间火花呈兰白色,光束集中,并发出:“啪、啪”响声。说明点火系统正常。 b.若电极间火花暗红色,光束分散,     

燃气轮机连续弧等离子点火器仿真与实现

文章建立了适用于燃气轮机的连续弧等离子点火发生器稳定电弧的有限元数学模型,采用多物理场耦合的计算方式对等离子弧的温度场、电磁场、速度场以及电极表面的电流密度进行了数值模拟。按照数值模拟结果修改了等离子点火发生器喷嘴结构设计。通过试验,可实现小电流激发空气等离子体并获得稳定的等离子射流火焰,满足燃气轮机可靠点火的要求。     

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%.     

Contents in Volume 23,2014

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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。     

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.     

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.