汽油机富氧燃烧过程火焰传播模型研究

针对汽油机的燃烧特点,研究汽油发动机富氧燃烧技术及燃烧过程中氧元素的作用机理,从燃烧火焰传播速度出发,把进入气缸助燃的空气中氧气的体积分数作为主要因素,建立汽油发动机富氧燃烧火焰湍流传播模型,来反映汽油燃烧的速率和燃烧火焰的传播特征.在Honda G200汽油机上进行了相关试验,结果表明,所提出的富氧火焰传播模型能够较好地模拟汽油发动机的燃烧及动力性能.     

水分变化对固定床内模拟城市固体垃圾燃烧的影响

实验研究了焚烧过程中固定床内温度、烟气成分浓度、火焰传播速度和质量燃烧速率的变化规律.实验结果表明:在物料燃烧稳定阶段,火焰传播速度几乎是恒定的,并且随着水分含量的增加,质量燃烧速率和火焰传播速度降低;NO的浓度变化曲线一般存在两个峰值;水分较高物料燃烧时,CO和NO的平均排放浓度较低;火焰的长度与水分含量成反比.     

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.     

氢气和水蒸气对甲烷/空气层流火焰传播速度的影响

为了较为系统地认识氢气和水蒸气对火焰传播的影响，应用CHEMKIN-Ⅱ程序计算了甲烷/空气层流预混火焰传播速度，并就水蒸气和氢气对火焰传播速度的影响做了定量计算与分析．结果表明：氢气能使火焰传播速度大幅提高，且当初始温度升高时，氢气对火焰传播速度的提高作用增大；水蒸气的加入会使甲烷/空气层流预混火焰传播速度降低，并且在空气过量时燃料越少其影响越弱；当氢气和水蒸气同时加入预混气时，水蒸气的加入会使氢气对火焰传播速度的提高作用减弱．     

逆风和静止环境中火焰沿柱状燃料传播的实验研究

本文测量不同直径的ＰＭＭＡ燃料捧在逆风和静止环境中的火焰传播速度，裂解长度和火焰形状，实验结果表明，在相同的燃料直径下，逆流风速越大，火焰传播速度较小，裂解区长度越小。火焰形状越平；在相同的逆流风速下，（１）当逆流风速于０．７ｍ／ｓ时，燃料直径越大，火焰传播速度越小；（２）当逆流风速大于０．７ｍ／ｓ时，燃料直径越大，火焰传播速度越大，当逆流风速较大时，不同直径燃料的无因次裂解长度趋现一致。     

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.     

微细通道中甲烷与氧气的预混燃烧

对微细通道中甲烷/氧气预混火焰传播性质进行了实验研究．确定了微细通道中不同甲烷浓度下的火焰传播速度,以及混合气体流量与火焰传播速度的关系．结果表明,混合气体流量对火焰传播速度有显著的影响,在微细通道中火焰传播速度的分布趋势与宏观尺度下火焰传播速度的分布趋势基本相同,但在数值上随着流量的不同相差较大．实验证明,在室温条件下,甲烷和氧气预混火焰可以在细管中稳定停留在一点燃烧,并且可以很好地控制其移动;当量比为1．0时火焰传播速度受流量影响最大．     

材料厚度对火焰向下传播特性的影响

在常重力静止空气环境中对厚度连续变化的聚甲基丙烯酸甲酯(PMMA)平板表面火焰向下传播进行实验研究,分析了材料厚度对火焰传播特性的影响.结果表明,材料厚度增加时,火焰长度和材料热解长度单调增加,而当材料厚度减小时,材料热解长度和火焰长度先增加后减小.在这两种情况下,均存在热薄材料和热厚材料的转变厚度,其值与文献中使用均匀厚度材料得到的实验结果及理论预测一致;材料厚度小于该转变厚度时,火焰传播速度与材料厚度呈反比关系,大于该厚度时,火焰传播速度不随材料厚度变化,这分别符合热薄材料和热厚材料火焰传播速度的理论模型.     

2-甲基呋喃及其与异辛烷掺混燃料燃烧特性的可视化

由于2-甲基呋喃(MF)的喷雾与燃烧特点与汽油类似,其作为替代燃料的潜力受到广泛重视.利用光学发动机和高速摄影技术,结合热力学分析,对MF以及其与异辛烷掺混燃料的湍流火焰传播特性进行了研究.结果表明:与异辛烷相比,MF有更高的燃烧爆发压力和较短的滞燃期,同时其火焰面积扩展速率也高于异辛烷.研究发现火焰传播面积与已燃质量分数(MFB)的2/3次方呈线性关系.MF的湍流火焰传播速度明显大于异辛烷,二者的差别比这两种燃料层流火焰传播速度的差异更加明显.混合气的物理化学特性是影响湍流火焰传播速度的最大因素.     

天然气-氢气-空气混合气火焰传播特性研究

在定容燃烧弹内研究了初始条件为常温常压的灭然气-氢气-空气混合气火焰传播规律,得到了不同掺氢比例和燃空当量比下混合气的层流燃烧速率、质量燃烧流量和马克斯坦长度,结合火焰传播照片,分析了火焰的稳定性并预测了大尺寸火焰稳定性的演变趋势。研究结果表明,随着天然气中掺氢比例的增加,混合气的燃烧速率增加,且增长速率逐渐加快,马克斯坦长度值减小,火焰的稳定性下降。各种掺氢比例下,随当量比的增加,马克斯坦长度值增加,火焰的稳定性增加。掺氢比例高于80％时,随着火焰的传播,其不稳定性将明显增加。     

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。     

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.