柴油机润滑系统各元件对工作压力的影响分析

通过对柴油机润滑系统的工作原理和各元件在系统回路中的作用进行描述,对影响系统工作压力的因素进行分析;对主油路调压阀、滤清器旁通阀、机油冷却器旁通阀在系统中的作用及其工作特点进行论述。通过研究分析后得出,要保证柴油机润滑系统能处于最佳工作状态,不但要求进行仔细的系统设计,对零部件的设计和质量控制也十分关键。     

柴油机机油滤清器旁通阀特殊故障分析

柴油机机油滤清器设置旁通阀是为了保证柴油机的正常润滑．当机油滤清器堵塞时，机油可通过旁通间进人油道继续润滑柴油机．在机油滤清器正常工作时，旁通阀通常处于常闭状态，只有在机油滤清器严重堵塞的极特殊情况下，旁通间才会处于开启状态．1旁通间工作状态分析由于机油滤清器滤芯的定期清理或更换，所以在柴油机使用期内，除极个别旁通阀偶尔在工作状态开启一两次外，绝大多数旁通网都一直处于常闭状态．102系列柴油机机油滤清器的旁通间开启压力一般为137kPa，当两端的压差超过137kPa时，机油推动旁通阀的阀芯压缩弹簧后移，当闭芯…     

车用汽油机活塞销座轴承润滑特性

利用活塞、连杆系统多体动力学分析结合弹性流体动力学润滑(EHL)模型,研究了活塞销座轴承的润滑特性.首先建立了活塞、活塞销和连杆的有限元模型,利用Craig-Bampton方法对其进行了自由度缩减以降低求解规模,然后在活塞销座轴承和连杆小头轴承引入EHL润滑模型,计算了活塞销座轴承的油膜厚度、油膜压力和干接触压力等轴承润滑特性参数.研究了是否考虑活塞和活塞销的结构弹性及油膜空穴对计算结果可能产生的影响,分析了活塞销孔间隙、活塞销刚度和活塞销孔几何形状等参数对其润滑特性的影响,用不同形状销孔的润滑特性计算结果解释了发动机热拉伤试验中出现的活塞销孔拉伤情况.结果表明:活塞和活塞销的结构弹性及油膜空穴是汽油机活塞销座轴承分析中不可忽略的影响因素;活塞销刚度和活塞销孔几何形状对活塞销座轴承润滑特性有重要的影响.     

活塞裙部流体动力润滑数值分析

对内燃机活塞-缸套系统的流体动力润滑与动力学行为进行了耦合分析,在考虑活塞二阶运动的基础上建立了活塞裙部润滑的数值模型。运用龙格-库塔方法求解二阶运动模型,并采用有限元方法求解裙部润滑的平均雷诺方程。分析了裙部不同型线、活塞销不同偏置的油膜厚度、油膜压力和活塞摆角等二阶运动状况。在润滑油不同粘度以及是否考虑粘压特性条件下,对油膜摩擦力和摩擦功率进行了对比。结果表明,裙部采用中凸椭圆型线,活塞销向主推力侧偏置,可减小二阶运动,改善润滑状态,润滑油粘度对裙部摩擦损失有较大的影响,而粘压特性则对裙部润滑的影响较小。     

活塞裙部的润滑分析及活塞系统2阶运动的研究

基于平均流量型分析了活塞裙部的润滑问题，并且与活塞运动方程结合求解了活塞系统２阶运动的轨迹，探讨了活塞结构参数对２阶运动 的影响，计算和比较了在不同参数下活塞初部的摩擦力。     

某船用大功率柴油机拉缸故障分析

针对某船用大功率柴油机运行过程中的拉缸故障进行拆检分析和有限元仿真研究.分析与研究结果表明:润滑油喷嘴堵塞影响了活塞热量散发和气缸套有效润滑,在高负荷下加速了零件磨损,进而导致拉缸故障.不同负荷下,活塞、气缸套和活塞环均向外部膨胀,活塞与气缸套间存在足够的热膨胀余量;而活塞环与气缸套间将出现过盈配合,在高负荷和润滑失效...     

基于Hydsim的高压共轨电控喷油系统喷油特性仿真分析

为了深入研究柴油机喷油系统关键结构对喷油特性的影响,运用Hydsim软件建立系统仿真模型,通过改变进出油节流孔和控制活塞的结构参数,分析其对喷油特性的影响。仿真结果表明:随着进油节流孔面积增大,针阀开启速度变慢,落座速度加快;随着出油节流孔面积增大,针阀开启速度加快,落座速度影响不大,在满足喷油要求的前提下出油节流孔面积应取较小值;随着控制活塞直径增大,针阀开启速度变慢,落座速度变快。可以依据针阀升程和喷油率的仿真曲线,选择适当范围的结构参数。     

考虑活塞热变形的活塞裙部润滑计算分析

采用三维有限元方法进行了柴油机活塞的热分析 ,计算得到了活塞的热变形 ,建立了活塞裙部考虑热变形的流体动力润滑模型。利用这个模型进行了考虑活塞裙部热变形的润滑计算 ,通过和冷态的润滑计算结果对比 ,发现热变形对活塞的润滑性能有很明显的影响 ,应在活塞裙部设计中予以考虑。     

船用柴油机进排气旁通阀开启工况和控制策略研究

使用相继增压技术可以充分发挥高速、高功率密度船用柴油机的性能优势,但是在相继增压技术的使用过程中,依然存在涡前排温超限和增压器喘振等风险。尤其是在船机推进加载的瞬态过程中,喘振现象的出现会极大地影响加载时间。为了降低上述风险,本文对进排气旁通阀开启工况和控制策略进行了研究。研究结果表明:稳态工况时,开启进排气旁通阀,有利于降低低速外特性工况的涡前排温和烟度;瞬态工况时,开启进排气旁通阀,可以降低增压器喘振风险,从而使瞬态推进加载时间从120秒缩短到30秒。此外,先进的控制策略可以使进排气旁通阀在增压器瞬态切换工况时更精准地发挥降低喘振风险的作用。     

高增压船用柴油机低负荷降低涡轮前排气温度的方案研究

采用仿真和试验相结合的方法,研究高增压船用柴油机推进特性低负荷降低涡轮前排气温度的方案。通过仿真计算发现,由于受活塞和气门型线的限制,进/排气门正时优化的改善效果不明显;而进/排气旁通可大幅降低涡轮前排气温度,同时改善低负荷下的油耗。进/排气旁通系统在柴油机的试验测试表明其能够大幅降低涡轮前排气温度,最多可达120℃。     

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。     

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.