柴油混合燃料液滴微爆现象及规律研究

选用甲醇-柴油乳化液滴和正己烷-柴油互溶液滴作为试验对象,采用飞滴式单液滴方法,研究了高温环境下燃油液滴的微爆现象及其规律．通过研究甲醇-柴油乳化液滴和正己烷-柴油互溶液滴的微爆过程,对比了互溶柴油液滴及乳化柴油液滴进行膨胀破碎的差异性,结果发现：互溶燃油液滴可观察到明显的气泡融合过程;相比于互溶燃油液滴,乳化油液滴的破碎发生更早,膨胀速率更快,但膨胀比较小．探究了甲醇体积分数和液滴初始直径对甲醇-柴油乳化油液滴微爆过程的影响发现,甲醇体积分数增加对乳化油液滴微爆起先促进后抑制的作用．随甲醇体积分数的增加,乳化油液滴的破碎时刻先提前后推迟,膨胀比先增大后减小;在甲醇体积分数为30%时,乳化油的微爆效果达到最优．最后对比了两种不同程度的微爆现象发现,整体微爆的膨胀速率和膨胀比均大于局部微爆,发生整体微爆的液滴雾化效果更好．相同条件下液滴发生不同程度微爆的原因是气泡的生成位置不同．     

微重力下生物柴油预混醇类燃烧与微爆特性实验研究

以生物柴油预混醇类液滴,利用落塔的自由落体方式达到微重力燃烧实验。实验结果发现生物柴油预混醇类时会有内部不均匀现象,其与湿度无关,且在燃烧时会直接导致微爆。燃烧速率分析结果发现醇类加入生物柴油液滴有助于增加其燃烧速率,在不微爆时,混合液滴在醇类重量百分比为25%时达到最高;在微爆状况下,则在50%时因微爆最剧烈而使平均燃烧速率最高。     

苄基叠氮复合柴油液滴蒸发特性及影响因素的试验

为了探明苄基叠氮复合柴油实现快速燃烧的根本原因,在挂滴试验装置上研究了不同配比的苄基叠氮复合柴油液滴的蒸发特性,利用高速摄像技术观察了初始直径为1.42,mm的液滴蒸发过程中的形态变化,并对比分析了环境温度对液滴蒸发特性的影响.结果表明,与柴油相比,苄基叠氮复合柴油液滴蒸发历程发生根本变化,随着浓度的增加,液滴生存时间明显缩短,而且观察到了喷气、微爆等现象,这一强烈的反应是苄基叠氮化合物液相分解高速释放出的氮气所引起的.另外,环境温度升高,液滴微爆强度增加,提高了液滴蒸发速率.     

柴油-麻疯树生物柴油单液滴蒸发特性试验

为探明柴油-麻疯树生物柴油混合燃料的蒸发过程与机理,达到生物柴油多是与柴油混合用于柴油机缸内稳定燃烧的目的,通过碱性酯交换方法制备生物柴油,并采用热电偶挂滴技术,研究不同掺混比例麻疯树油在环境温度623 K和873 K下的蒸发特性。结果表明:低温下,柴油的液滴寿命为3. 663 s/mm~2,随着麻疯树生物柴油的掺混比例的增大,液滴有较长的蒸发寿命,JME100(纯麻疯树生物柴油)的液滴寿命约为JME10(柴油中混10%的麻疯树生物柴油)液滴寿命的2. 3倍;高温下,寿命最短的柴油液滴和寿命最长JME100液滴的寿命分别为1. 818 s/mm~2和JME100的3. 61 s/mm~2,相比于623 K环境温度明显缩短;同样,混合液滴平均蒸发率k会随着温度的提高而显著增大。     

柴油-生物柴油混合喷雾过程的多组分蒸发模拟

针对多组分混合燃料的喷雾过程研究了相应的液滴蒸发模型,着重于研究混合燃料的组分对其液滴蒸发特性的影响.对柴油-生物柴油混合燃料的液滴蒸发模拟,依据燃料本身的特点,分别采用连续热力学方法和离散组分法描述其中柴油和生物柴油的组成.利用所得模型,对单组分燃料、双组分燃料以及生物柴油的液滴进行了蒸发模拟,通过将液滴蒸发历史曲线与试验结果对比,发现对于这些燃料液滴的蒸发模拟结果与相应试验数据很好地吻合,证实了此混合燃料液滴蒸发模型的正确性.此外,还着重对柴油-生物柴油的混合燃料的液滴进行了蒸发模拟研究,探讨混合燃料成分对其液滴蒸发特性的影响.结果表明:轻质柴油组分在蒸发过程中优先蒸发,而相对重质的柴油组分的蒸发则相对滞后,生物柴油在混合燃料中的质量分数则在液滴蒸发过程中不断增加,随着重质组分在柴油中所占比例达到一定程度之后,生物柴油的质量分数则开始迅速减小.     

ABE/柴油单液滴燃烧微爆现象的试验

开展了丙酮(A)、丁醇(B)和乙醇(E)按照3∶6∶1的比例混合而成的溶液(ABE)/柴油混合燃料的静态和动态单滴油试验,静态单滴油试验结果表明,掺混30%～70%ABE在柴油中,其液滴内部会发生微爆现象,ABE50(ABE溶液占总的混合溶液体积的50%)微爆程度最剧烈,原因是该组分比例下气泡生成最多,液滴燃烧速率最快.动态单滴油试验是在自由落体条件下进行的,得到了与静态试验相同的结论.研究表明:4种燃料的燃烧速率为ABE50ABE30ABE70D100(纯柴油);而且,较之柴油液滴周围所形成的明显的球形碳烟壳,当ABE含量大于10%液滴周围几乎没有碳烟生成,证明了ABE能够有效抑制碳烟的生成.     

乳化油微爆的统一模型

关于乳化油的微爆在以往的文献中提出过各种计算模型,对油包水与水包油两种乳化油的微爆有不同看法。提出一种油包水与水包油微爆的统一模型并给出了微爆强度的定义,试图对微爆的强弱做定量的描述。通过该模型讨论了一些主要因素,如液滴初始直径,分散相直径及水含量等对微爆强度的影响规律。计算结果表明,该模型的理论预测与实验事实基本一致。另外还讨论了其他因素如添加剂的性质、气体溶解度等的作用。     

柴油机燃烧乙醇-柴油-生物柴油混合燃料的排放特性研究

在一台单缸直喷式柴油机上分别燃用柴油、乙醇-柴油-生物柴油混合燃料,对不同掺烧比的乙醇-柴油-生物柴油混合燃料的排放特性进行了对比研究.试验结果表明,随着乙醇掺混比例的增大,燃用乙醇-柴油-生物柴油混合燃料的排放情况是:烟度排放大幅度降低,中高负荷下CO排放大幅度减少,HC排放量明显增加,Nox排放变化不大.     

基于微流体技术的生物燃料开发与应用

为了加快生物燃料产业的发展速度,提高生物燃料的产量和质量,微流体技术被引入到了生物燃料领域。文章聚焦于微流体技术在生物燃料领域的应用,重点介绍了微流体技术及装置在生物柴油和生物乙醇生产中的应用,讨论了影响生物燃料微流体反应器性能的相关因素,最后,提出了微流体技术在生物燃料领域的应用过程中所面临的问题并展望了其应用前景。     

柴油-甲醇微乳化燃料的制备及燃烧特性研究

本文根据乳化和微乳化理论选择油酸作为表面活性剂配制了多种配比的柴油 甲醇微乳化燃料。微乳化燃料获得了与柴油相近的发动机动力性和热效率,NOX排放比燃用柴油时高,碳烟排放比燃用柴油时低。随供油提前角的推迟,NOX排放快速下降,碳烟排放变化不大,推迟供油可使甲醇混合油获得更好的排放水平。由于甲醇汽化潜热大、乳化燃料具有微爆效应,故在小负荷时混合燃料滞燃期比柴油时大,而在大负荷时两者较接近。随混合油含醇率的增加,预混燃烧峰值也随之增加。     

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.