车用稀燃天然气(CNG)发动机的开发研究

采用稀薄燃烧方式，是降低发动机排放和改善经济性的有效手段。在以柴油机为原型机开发的单燃料天然气发动机中，对进气系统和燃烧系统等进行了优化设计，采用了增压中冷、多点顺序喷射、高能直接点火以及综合电控技术，使之达到空燃比的精确控制和高能点火，以实现天然气的稀薄燃烧。同时对研制的样机在稀薄燃烧状态下的性能进行了试验研究，获得了良好的经济性和排放性能。     

电控多点喷射天然气发动机的开发

进行了柴油机改为天然气发动机的进气系统、燃烧系统、天然气供给系统、点火系统和电控系统等的设计．通过采取高效稀薄燃烧控制方案,实现了不采用EGR情况下NOx排放物的有效控制,仅匹配氧化催化转化器, 发动机排放即可达到欧Ⅲ(ESC)法规要求．同时,通过改进活塞环及活塞结构,解决了由柴油机改为天然气时发动机机油消耗量过高的问题．试验结果表明,CA6SE1-21N天然气发动机不仅达到了原柴油机的标定功率水平,而且具有良好的可靠性．     

柴油/天然气双燃料发动机柴油燃烧策略的研究

基于自主研发的第三代并行式柴油/天然气双燃料发动机电控系统,利用FIRE软件建立柴油/天然气双燃料发动机柴油喷射系统的多次喷射模型。同时,通过进气压力控制过量空气系数,实现柴油/天然气双燃料发动机稀薄燃烧方式。针对高负荷工况,研究了多次喷射策略和稀薄燃烧方式对双燃料发动机最大压力升高率及NOx排放的影响。结果表明:发动机工作在高负荷及柴油替代率为80%时,采用双燃料稀薄燃烧方式能使NOx排放降低,但最大压力升高率仍可能超过安全临界值1MPa/(°)。采用合适的预喷射量与预喷射时刻能降低最大压力升高率。通过多次喷射和稀薄燃烧方式相结合的燃烧策略对缸内燃烧方式进行组织,可以实现双燃料发动机高替代率燃烧,并使高负荷时NOx排放达到或者低于国Ⅴ标准限值。     

机组用天然气发动机开发

以某V型增压水冷柴油机为原型机,新开发HC8V132G机组用天然气发动机。对柴油机进行冷却系统、燃烧系统、进气系统等重新设计,匹配燃气供给系统、点火系统和电控系统。对发动机进行了传感器和性能标定。采用高效稀薄燃烧控制策略,通过氧传感器采集尾气中的O_2含量计算空燃比,控制燃气Trim阀开度,实现燃气进气量的调整,完成发动机实际空燃比和设定空燃比闭环控制。试验结果表明,新开发的机组用天然气发动机达到了功率设计要求。     

6230SG型天然气发动机研发

在对原有的6230柴油机实施技术改造的基础上,进行6230SG型天然气发动机开发.6230SG型天然气发动机遵循稀薄燃烧原理,采用预燃烧室电火花塞点火,逐缸控制燃气进气正时,燃气-空气混合良好,采用每缸一套机械式燃气控制机构设计.型式试验结果表明:6230SG天然气发动机的各项主要技术指标均达到设计要求.该机获得了中国船级社颁发的天然气发动机型式认可证书,实际应用达到预期要求.     

预燃室点火控制对大功率稀燃天然气发动机性能影响的试验研究

介绍了大功率天然气发动机采用的稀薄燃烧的技术特点,以及为实现稀薄燃烧所采用的预燃室点火控制的主要结构和特点。为研究预燃室点火控制对于发动机性能的影响,设计了三种不同类型的试验方案,分别对预燃室进气喷射提前角、预燃室进气喷射压力、预燃室进气喷射持续期进行试验研究,为大功率稀燃天然气发动机性能优化提供了技术依据。     

基于可变循环的气体发动机T ie rⅢ排放方案展望

根据远洋船舶航行特点,构想了一种基于可变热力循环,使气体发动机能够兼具高压气体发动机和低压气体发动机优点的Tier Ⅲ排放方案。希望通过天然气预混合、可变压缩比、引燃优化、燃烧速率控制、空燃比控制等技术的组合应用,实现均质稀薄燃烧,降低NO_x排放,使高压气体发动机在不使用EGR和后处理技术的情况下,达到IMO Tier Ⅲ标准。     

车用天然气发动机关键技术研究与发展

阐述国内外车用天然气发动机技术的最新进展及关键技术,包括结构设计、稀薄燃烧、空燃比控制、高能量数字点火和后处理技术等。并对未来新型技术在天然气发动机领域的应用前景进行分析和展望。     

船用预燃室式天然气发动机稀薄燃烧特性试验

以船用预燃室式天然气发动机为研究对象，以点火正时(SOI)和过量空气系数(φ_a)为变量开展缸内稀薄燃烧特性影响规律的研究．在此基础上对试验数据开展主效应和帕累托分析，得出量化的规律性结果．结果表明：一方面，影响着火延迟和燃烧放热速率权重较大的为SOI，通过优化可以将滞燃期缩短至12°CA以内，将燃烧重心控制在14°CA ATDC以前；而对于燃烧持续期，影响权重较大的为φ_a，将各工况下φ_a控制为1.66～1.84，可以将燃烧持续期控制在28°CA以内；另一方面，φ_a的运行范围已经达到并超过了车用重载的稀薄极限．由于采用了独立供气的预燃室形式，船用预燃室式天然气发动机可在缸径较大、平均有效压力(BMEP)较高的前提下实现比重载天然气发动机更加稀薄的燃烧组织，从而有利于实现较高的热效率，同时更好的兼顾NO_x排放．     

天然气直喷发动机当量比与稀薄燃烧对比研究

针对一台自然吸气四缸天然气缸内直喷发动机,建立了发动机仿真模型,通过台架试验数据对模型进行了验证。开展了均质当量比燃烧和稀薄燃烧两种方案的整机动力性、热负荷和经济性对比研究。结果表明：稀薄燃烧时动力性下降明显,当量比燃烧时热负荷较高,空燃比稍大于当量比时经济性最好。     

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.