压缩比、CO2和LPG对二甲醚燃料均质压燃燃烧的影响

在一台2-135柴油机上实现了纯DME的均质压燃(HCCI)燃烧方式.实验结果表明,DME的HCCI燃烧模式不但可以实现无烟燃烧,还可以有效控制发动机Nox排放,使其接近于零排放.在实验负荷范围内,CO排放随负荷增加而降低;HC的排放随负荷增大而减少.对DME的HCCI燃烧机理进行研究表明,由于纯DME十六烷值高导致的着火比较早(上止点前28°CA左右),使得发动机只能在中低负荷较小范围内运行.为了扩展发动机工况,控制HCCI着火,进一步通过调节实验发动机压缩比,以及在优化的压缩比下,在进气道加入气体CO2或者在DME中加入LPG降低燃料十六烷值的方法来改进和控制HCCI的燃烧.实验表明以上方法可以有效控制HCCI燃烧,拓宽HCCI发动机运转范围.     

废气再循环对二甲基醚均质压燃燃烧过程影响的试验研究

在一台单缸发动机上进行了废气再循环(EGR)对二甲基醚(DME)均质压燃(HCCI)燃烧过程影响的试验研究。结果表明，EGR比例小于20％对运行最大负荷工况范围影响不大；采用高比例EGR可以拓宽DME均质压燃运行工况范围，随着EGR率增大，HCCI运行的最大负荷工况增大，着火燃烧时刻推迟，燃烧放热率降低，缸内最大爆发压力降低，发动机热效率增大；EGR率小于75％，HC排放略有降低或相当，EGR率为75％时，HC排放显著增加；EGR率大于25％，随着EGR率增加，CO排放增大，小负荷工况尤其明显，在中高负荷工况，EGR率对CO排放影响较小。     

废气再循环对二甲醚/天然气双燃料均质压燃燃烧过程和排放特性的影响

在一台单缸直喷式柴油机上研究了冷却废气再循环(EGR)对二甲醚(DME)／天然气(CNG)双燃料均质压燃(HCCI)燃烧过程和排放的影响．结果表明，EGR率加大，着火时刻滞后，放热速率降低，燃烧持续期延长，DME比例加大，着火始点提前，放热率峰值上升，燃烧持续期缩短，EGR率增大，发动机“失火”和爆震燃烧的DME比例增大，但“失火”和爆震燃烧之间的DME比例区间变宽，EGR可以拓宽HCCI发动机的工况范围．对应不同比例的EGR，有一个热效率最佳的DME比例区域．HC排放和CO排放随EGR率的增高而增加，随DME比例的增大而降低．NO。排放在不发生爆震的情况下保持在极低的水平．因此，控制DME比例和EGR率是控制DME／CNG双燃料HCCI发动机燃烧过程、性能和排放的关键。     

DME/LPG燃料比例实时优化的HCCI燃烧控制新方法

根据燃料设计的思想，提出了混合燃料比例实时优化的HCCI燃烧控制新方法。在一台2135柴油机上，通过燃料成分设计（DME／LPG混合燃料）、混合气成分设计（进气添加二氧化碳）、发动机参数调整（改变压缩比）等多种模式对二甲醚HCCI燃烧进行了研究和比较。试验结果表明，在不同工况下实时进行DME／LPG比例优化，通过改变燃料的理化特性和可燃混合气的成分，实现了HCCI着火与燃烧的有效控制，能够显著拓展二甲醚HCCI燃烧的运行负荷范围，并且各个工况下热效率最高、HC和CO排放最低。     

废气再循环对二甲醚/甲醇均质压燃燃烧过程影响的试验研究

在单缸柴油机上进行了冷却废气再循环(EGR)对二甲醚(DME)/甲醇均质压燃(HCCI)燃烧过程影响的试验研究。结果表明,EGR对拓宽二甲醚/甲醇HCCI发动机的最大负荷作用不大;随着EGR率增大,主燃烧开始时刻和放热峰值明显后移,主燃烧持续期延长,放热峰值降低。EGR率为25%时的最大爆发压力比没有EGR时降低了近1.3 MPa,最大爆发压力出现的位置推迟了7°CA;EGR率增大,二甲醚/甲醇HCCI发动机的指示热效率升高。对应给定的EGR率,存在一个热效率较高的DME比例区间;HC和CO排放随EGR率的增大而增加,随DME比例的增加而降低,NOx排放接近于零。控制EGR率和DME比例是控制二甲醚/甲醇HCCI发动机燃烧过程、性能和排放的关键。     

醇醚双燃料发动机均质压缩燃烧试验研究

以ZS195型直喷式柴油机为原型机,开展了进气道喷射醇醚混合燃料HCCI试验研究。试验研究结果表明,甲醇的添加能够抑制二甲醚(DME)低温反应,降低缸内最大爆发压力和燃烧温度,推后主燃烧反应时刻,解决二甲醚的过快和过早燃烧,可以有效调节HCCI着火时刻和扩展其运行工况。双燃料HCCI发动机的指示热效率最高可以达到49%左右,超过原柴油机10%。通过调节甲醇喷油量,可实现HCCI燃烧着火点可控以及扩展HCCI发动机运行负荷范围。     

压缩比对汽油HCCI燃烧和排放特性的影响

通过优化动力技术对一台四缸汽油机进行改造设计,实现均质混合气压燃(HCCI),考察了压缩比对汽油机HCCI负荷拓展及冷却液和进气温度对HCCI燃烧排放特性的影响。试验结果表明:提高压缩比可以在更低的进气温度下实现SI/HCCI燃烧模式的切换,CO排放升高,HC排放下降,NOx排放呈下降趋势,且在高负荷工况时下降得更加明显。在压缩比为15时,HCCI汽油发动机可以在1 200~3 600r/min转速范围内实现稳定燃烧,提高压缩比有效拓展了HCCI发动机负荷范围。随着进气温度及冷却液温度的升高,燃烧相位提前,燃烧持续期缩短,缸内压力、放热率及温度升高;缸内循环变动率减小,实现更稳定的HCCI燃烧;CO、HC排放也随之降低,但NOx排放有升高趋势。     

二甲醚均质充量压燃发动机排放特性的试验研究

试验研究了压缩比为10．7的二甲醚均质充量压缩点燃燃烧发动机的排放特性。试验结果表明，采用DME HCCI燃烧方式可以有效控制发动机的氮氧化合物排放，使其接近于零，实现无烟燃烧。在一定的负荷范围内，发动机的碳氢和一氧化碳排放与柴油机相当；低负荷时混合气过稀，则碳氢和一氧化碳排放偏高，而高负荷混合气过浓时，又有可能导致敲缸。发动机稳定运转的条件是一定的空燃比必须对应一定的发动机转速和负荷。     

二甲醚发动机采用PCCI-DI燃烧方式的研究

开展了DME PCCI-DI发动机燃烧和排放特性的试验研究,并与DME HCCI发动机的性能进行了对比.结果表明:DME PCCI-DI发动机的输出功率在一定程度仍然受到均质浓混合气燃烧爆震的限制,但发动机的功率输出较DME HCCI发动机有较大的提高.HCCI发动机的Nox的排放能维持在非常低的水平,但其HC和CO排放远高于DME PCCI-DI发动机,且其只能在很窄的范围内工作.由于DME PCCI-DI发动机具有一定的预混燃烧量,从而使扩散燃烧速率加快,是一种具有最高爆发压力较小、压力升高率较低以及低燃烧噪声的一种燃烧模式.在目前HCCI发动机没有完全成熟的条件下,PCCI-DI模式是兼顾HCCI燃烧优点,拓宽HCCI发动机运转范围的较为合理的一种燃烧模式.     

DME/柴油混合燃料HCCI燃烧与排放特性的试验研究

在单缸柴油机上采用轴针式喷嘴进气道燃油喷射方式,开展了二甲醚(DME)/柴油混合燃料预混均质压燃(HCCI)燃烧及其排放特性的试验研究,探讨了喷油嘴启喷压力、进气温度以及进气掺混不同比例CO2对混合气制备率和发动机性能的影响.结果表明:低沸点液相DME在进气道喷射过程中所具有的闪急沸腾效应,可有效强化柴油/DME混合燃料的雾化与蒸发,减少燃油撞击壁面而出现的进气歧管壁湿现象,从而改善柴油HCCI发动机均质混合气的形成与燃烧,拓宽发动机的运行工况范围.进气掺混0~30%的CO2能使HCCI发动机的正常工作范围从0.32MPa提高到0.5MPa,实现高负荷工况下同时降低NOx和碳烟的排放,但CO和未燃HC排放有所增加.     

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.     

Wind power for pumping: The development of the ITP windpump

Water pumping has been one of the main applications for wind power in the past and despite the spread of mains-electric pumps, more than a million windpumps remain in regular use. This paper reviews the general technical and economic requirements for pumping water using wind energy and by way of example gives an overview of the development of the new ITP wind-pump. It then considers the future prospects for this kind of technology.     

Methods of creating solar-reflective nonwhite surfaces and their application to residential roofing materials

We describe methods for creating solar-reflective nonwhite surfaces and their application to a wide variety of residential roofing materials, including metal, clay tile, concrete tile, wood, and asphalt shingle. Reflectance in the near-infrared (NIR) spectrum (0.7–2.5 μm) is maximized by coloring a topcoat with pigments that weakly absorb and (optionally) strongly backscatter NIR radiation, and by adding an NIR-reflective basecoat (e.g., one colored with titanium dioxide rutile white) if both the topcoat and the substrate weakly reflect NIR radiation. Coated steel and glazed clay-tile roofing products achieved NIR reflectances of up to 0.50 and 0.75, respectively, using only cool topcoats. Gray-cement concrete tiles achieved NIR reflectances as high as 0.60 with coatings colored by NIR-scattering pigments. Such tiles could attain NIR reflectances of up to 0.85 by overlaying a white basecoat with a topcoat colored by NIR-transparent organic pigments. Granule-surfaced asphalt shingles achieved NIR reflectances as high as 0.45 when the granules were covered with a white basecoat and a cool color topcoat.     

Thermal decay of an initially hot isothermal water body with application to thermal energy storage

The thermal decay of an initially hot isothermal water body contained in a tank was studied. Analytical solutions (including a group-theoretic solution) were obtained for the one-dimensional heat conduction equation with heat loss from the sides of the tank. The convective heat transfer coefficient was assumed not to be constant over the surface of the tank but to vary with space and time. A very good agreement was obtained between the group-theoretic solution and a numerical solution using the Crank-Nicholson finite difference scheme. The analytical results are discussed in terms of the underlying physical mechanisms.     

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.     

秸秆燃烧中温度对钾转化与释放的影响

通过对稻秆原料进行常规特性分析和EDX元素含量分析,发现钾在稻秆无机元素中占有重要地位。参考原料化学分馏法和土壤中钾的分类与测试方法,给出了对生物质原料及其燃烧产物中钾的定性与定量简易方法。通过程序控温型固定床对稻秆先进行缓慢氧化,然后以100℃为间隔从400～900℃进行成灰,并分别测试其成灰率、有效钾和全钾的份额。结合稻秆原料及其灰中钾的份额分析,进行了稻秆灰中有效钾转化与释放的计算,发现有效钾在700～800℃之间有快速的释放和形态转变。稻秆灰的XRD分析结果表明秸秆灰中钾主要以KCl、K_2SO_4形式存在,得到了钾以盐的形式进行转化与释放的机理。该文中燃烧温度对钾转化与释放的影响规律对设计秸秆电厂时的炉型选择和燃烧参数确定有一定参考价值。