污水污泥着火和燃烧特性研究

采用热分析的方法对4个污水处理厂的污泥在空气气氛下的着火燃烧过程及其动力学特性进行了研究,分析了污泥着火机理,确定了污泥的着火温度和综合燃烧特性指数,提出污泥在空气气氛下的燃烧分3个阶段,第1阶段是水分析出阶段;第2阶段是有机物的分解燃烧和固定碳燃烧阶段,这一阶段是污泥燃烧的主要失重阶段;第3阶段是无机物的分解阶段.其中第1个阶段是吸热过程,第2阶段是放热过程.采用双组分分阶段一级反应模型求出了4个污泥样品的表观活化能和指前因子,给出了样品热解的动力学方程,通过理论计算,双组分分阶段一级反应模型的理论数据与实验数据吻合良好.     

二甲基醚燃烧过程及其优化的数学模拟（Ⅰ）——燃烧模型

在定容燃烧弹实验和发动机台架实验基础上建立了二甲基醚DME燃烧过程的准维多区的现象学燃烧模型,模型针对DME燃烧过程的特点,建立了新的喷雾混合和着火滞燃期子模型,修正了燃烧放热率子模型,研究了DME燃烧过程中氮氧化物（NOx)生成机理。模型的计算结果和实验结果相当吻合,模型对变工况、变参数有较好的适应能力。NOx生成历程计算分析表明,DME燃烧过程中NOx主要在扩散燃烧阶段生成,燃烧温度低是NOx排放低的主要原因。     

双燃料发动机的燃烧模型

针对双燃料发动机燃烧特性，建立了柴油喷雾扩散燃烧子模型和气体燃烧均质混合气火焰传播燃烧子模型，应用该模型研究了双燃料发动机燃烧机理，计算结果和实验结果相当吻合。计算表明：当引燃柴油比例较大时，双燃料发动机燃烧过程以喷雾混合控制燃烧为主，柴油喷雾扩散燃烧模型与实测较吻合；当柴油比例较小时，该过程以均质混合气火焰传播燃烧为主，均质混合气火焰传播燃烧模型与实测软吻合。计算结果表明，引燃柴油量对双燃料发动机性能影响较大，引燃柴油减少，着火滞燃期延长，缸内最大爆发压力升高。     

柴油引燃天然气发动机燃烧过程的研究

对柴油引燃天然气发动机的着火过程、燃烧过程进行研究,提出了相应的数学模型,并进行了试验验证。着火模型的基本框架仍然采用Shell模型,但考虑到CH4对柴油着火过程的影响,修正了Shell模型。对CH4的均质燃烧过程,以简单的一步表观反应动力学概念的阿伦纽斯(Arrhenius)公式为基础,综合湍流脉动对化学动力学的影响,提出了一个新的燃烧模型。模拟计算借助了KIVA-3软件,修正的Shell模型和燃烧模型作为独立子程序与KIVA-3进行了耦合。研究表明,讨论的模型能够较好模拟柴油引燃天然气发动机的着火和燃烧过程。     

几种生物质的TG-DTG分析及其燃烧动力学特性研究

采用热重分析技术对木屑、麦秆、玉米秆和玉米芯4种生物质的燃烧特性进行了研究,考察了其着火、燃尽特性和综合燃烧特性,研究了升温速率对生物质燃烧特性的影响,同时在热天平上对其进行了动力学试验研究.研究表明:生物质燃烧过程大致可以分为3个阶段,即水分析出阶段、挥发分析出燃烧阶段、固定碳燃烧与燃尽阶段:生物质具有着火温度低、燃尽温度低、燃尽率高等优点;随着升温速率的提高,着火温度、各试样挥发分最大释放速率、燃尽温度均呈升高趋势,燃烧特性随升温速率的提高而变好.采用一级反应动力学模型和积分法对生物质燃烧动力学参数的研究表明,生物质具有较低的活化能,有利于点燃.     

高喷射压力下柴油喷雾燃烧的试验及仿真

在定容弹中对高喷射压力下柴油喷雾着火燃烧开展试验及仿真,对不同喷射压力下喷雾蒸发过程及高压下柴油喷雾着火燃烧过程进行分析。结果表明：喷射压力越高,喷雾贯穿距越长,蒸发率更快,达到完全蒸发的时间越短。燃烧过程的仿真结果表明：喷雾着火呈现明显的双阶段特性,CH₂O质量分数和OH质量分数可分别表征第一和第二阶段着火;气相燃油达到高含量区时促发第二阶段成功着火。试验及仿真的碳烟呈现一致性趋势,浓碳烟主要集中在喷雾头部,与OH不同的是,碳烟在整个第二阶段的燃烧过程中持续存在。     

柴油机部分预混合燃烧与排放特性的模拟与试验

在一台6缸重型增压柴油机上,通过单次喷射策略结合EGR技术实现部分预混合燃烧(PPC)方式.基于Level-set的湍流火焰传播模型结合简化的化学反应机理对这种燃烧模式的燃烧与排放生成过程进行计算分析.依据试验和模拟结果分析PPC模式对燃烧放热、NOx、UHC和PM排放的影响.结果表明:早喷和晚喷PPC模式都具有两阶段的放热,在燃烧期内预混燃烧比例显著高于常规燃烧模式,但晚喷模式下还存在部分扩散燃烧;采用PPC燃烧方式可减少NOx和PM排放,但晚喷PPC模式下HC排放会增加;PPC模式下核心组分的变化过程和常规喷油模式有很大的不同,在PPC模式下酮化过氧氢在第一阶段着火过程中起到关键作用,第一阶段着火过程中积累的大量H2O2使得第二阶段着火过程中放热率峰值很高;在喷束下游生成OH的位置会生成大量NOx,而碳烟是在燃烧室壁面附近的富燃料区域形成,晚喷PPC模式下的HC排放过高主要是由于贫燃料区域不能迅速进行第二阶段着火引起的.     

柴油喷雾着火过程的化学动力学模拟

在直喷式柴油机准维燃烧模型的基础上,建立了能描述柴油机着火前燃油的氧化历程及着火滞燃期的多步着火化学动力学子模型,它不仅可以很好地模拟实际柴油机的燃油氧化过程,而且可以较好地反映着火滞燃期随各种因素的变化关系,比以往的描述着火滞燃期的经验模型更具有合理性和先进性。整个燃烧模型的计算结果及其与试验结果的对比还表明,本模型能够合理地预测柴油机的燃烧过程。     

废轮胎热解半焦的单颗粒燃烧特性实验研究

在单颗粒燃烧系统上研究了废旧轮胎热解半焦颗粒的燃烧特性，并探究了温度与颗粒粒径对燃烧的具体影响．结果表明，半焦颗粒在850℃及以下燃烧时经历挥发分析出及着火、挥发分燃烧、焦炭着火及焦炭燃烧4个阶段，在机理上属于典型的均质着火机理；在950℃以上时，焦炭着火早于挥发分着火，其着火机理转变为联合着火．此外，温度升高会缩短半焦颗粒着火时间等特征时间，而半焦颗粒粒径的增加则会增大挥发分火焰的体积并显著延迟焦炭的着火时间．研究结果为高效清洁利用轮胎衍生燃料提供了一定的基础研究数据．     

二甲醚均质压燃燃烧过程的试验研究

在一台单缸直喷柴油机上进行了二甲醚(DME)均质压燃(HCCl)燃烧过程的试验．研究结果表明，进气中加入30％的惰性气体CO2,发动机实现HCCl运转的负荷范围从0．05MPa扩展到0．35MPa．二甲醚在HCCl模式下表现出明显的双阶段着火特性，增加惰性气体的浓度，第一阶段着火始点滞后，燃烧放热峰值降低，燃烧持续期延长．排放测试表明，HCCl模式下发动机的NOx排放接近于零，可实现无碳烟排放，但CO和HC排放较高．     

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。     

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.