基于CFD的增压柴油机不同喷油提前角的排放影响分析

在考虑进气涡流比的情况下,对某490增压直喷柴油机不同喷油提前角下的缸内喷雾及燃烧过程进行了三维CFD模拟,给出了4种不同喷油提前角时的缸内火焰、NOx和Soot的时空分布.计算和分析了不同的喷油提前角下,上止点前后喷入缸内的油量比例、着火时刻、上止点温度、最高燃烧温度等对燃烧与排放物的影响.结果表明上止点前后的油量比例对排放有较大影响,对于该机型在喷油提前角较小的情况下,应考虑适当减小喷油锥角以充分利用燃烧室底部的空气.仅靠喷油提前角的变化并不能同时降低NOx和Soot的排量,并通过性能与排放试验进行了验证.     

某高原增压柴油机喷油提前角优化及性能研究

基于ECF-3Z燃烧模型建立适应高原环境的某增压柴油机工作工程模型,在平原台架试验验证的基础上,分析了喷油提前角对海拔4550m下缸内燃烧过程的影响。模拟结果表明:喷油提前角增大,缸内燃烧压力、温度曲线峰值上升且出现时间前移,燃烧重心提前,NOx排放上升,功率得到恢复;同时,缸内预混合燃烧得到强化,后燃期变短,燃烧室中心区域空气利用率得到提高。根据模拟结果选择提前6°CA喷油并在海拔4550m下对原机进行试验。试验结果表明:在调整喷油提前角后,功率提升了3.6%,涡前排气温度上升了46.6℃,燃油消耗率下降了1.4%。     

高功率密度柴油机的喷油时刻对燃烧排放的研究

运用AVL FIRE软件,建立某台单缸高功率密度柴油机模型,研究喷油时刻对该柴油机燃烧排放的影响规律,并用柴油机台架试验验证模型的合理性。着重仿真分析了不同喷油时刻对柴油机缸内压力、温度、放热率、功率、燃油消耗率以及排放的影响。分析结果表明:喷油时刻每提前3°曲轴转角,缸内压力和温度分别升高6.55%和2.8%;放热速率快,放热相对集中;NO_x排放增加,碳烟排放降低;功率下降,燃油消耗率升高;当喷油时刻为上止点前16°曲轴转角时,NO_x和碳烟排放都能满足排放法规要求,且动力性和经济性能较好。     

不同喷油提前角对缸内碳烟生成影响的计算与分析

应用计算流体动力学对某小型高速增压直喷式柴油机缸内燃烧过程进行了数值计算,得出了不同喷油提前角下增压直喷式柴油机缸内混合气、温度和碳烟的分布情况,分析了不同喷油提前角下,上止点前后的喷油量的比例对碳烟排放的影响,并通过实际工况下的碳烟排放试验进行了验证。为增压柴油机性能与排放优化提供了参考。     

喷油策略对自由活塞直线发动机燃烧过程的影响

研究不同喷油策略对自由活塞发动机燃烧排放性能的影响,探索了适合自由活塞发动机柴油燃烧系统的喷油策略。基于AVL FIRE仿真平台,搭建三维动网格计算模型,通过台架试验数据,对试验喷油策略为矩形的缸压数据进行标定,验证了模型的准确性。然后对4种不同曲线形状喷油策略(普通三角形、等腰三角形、矩形和梯形)下的发动机燃烧放热及排放性能进行了仿真计算。研究结果表明:压缩上止点前采用矩形喷油策略缸内油气混合速率最快,压缩上止点后采用等腰三角形喷油策略更有利于油气混合;等腰三角形喷油策略下发动机峰值燃烧压力最大,最接近上止点,而且指示热效率最大,达到0.371;等腰三角形喷油策略下,缸内峰值燃烧压力和温度最大,NO排放最高而碳烟排放最低。     

汽油/柴油混合燃料发动机小负荷工况的燃烧及排放特性仿真研究

针对汽油/柴油混合燃料发动机,在均质压燃(HCCI)模式,利用缸径100 mm单缸柴油机,控制喷油量在每循环9.4 mg,转速在2 000 r/min,进气压力在0.2 MPa时,选取不同汽油/柴油比例掺烧、在不同喷油时刻进行数值模拟研究,结果表明,汽油/柴油混合燃料随汽油比例增大,喷油时刻提前,缸内平均压力呈先增后减,燃料燃烧速度先减后增,缸内平均温度呈上升趋势,喷油时刻提前,可大幅度降低CO,NO,喷油时刻在止点后-30°曲轴转角(CA)到-40°CA之间时,增大汽油比例能有效降低碳烟(Soot);G50燃料会随喷油时刻提前,燃油混合气雾化效果变好,CO,NO会进一步降低,而Soot排放呈先减后增规律,整体排放降低的最优喷油时刻在上止点后-35°CA。     

自由活塞式内燃直线发电机的燃烧性能研究

对一台二冲程汽油自由活塞式内燃直线发电机(FPLG)的活塞动态特性、缸内压强、缸内温度和NO_x排放进行了数值分析。针对FPLG特点,具体分析了其NO_x污染物的来源及形成机理。借助于数值分析软件Matlab/Simulink,计算并分析了点火提前时间和燃烧持续时间对FPLG缸内压力、缸内温度和NO_x排放的作用。计算结果表明:点火时刻在上止点前171°~126°而燃烧持续时间为36°~108°曲轴转角(点火提前时间相对上止点前为0 6ms,燃烧持续时间在412ms)时,增大提前点火时间和缩短燃烧持续时间都会使缸内的压力和温度上升,相应的NO_x的排放量也会急剧增大。     

某型中速柴油机降低NOx生成与排放的改进研究

在测试与数值模拟的基础上,对某型中速柴油机提出改进方案,并进行了改进方案下的燃烧排放测试和缸内燃烧、排放过程的数值模拟,得到了缸内温度、压力以及NOx生成与排放量的变化过程.研究表明:改进方案的计算结果和台架试验结果较好吻合;对该机型实施的适当推迟喷油提前角,缩短喷油持续期的改进方案,可使NOx排放修正值由改进前的11...     

喷油控制参数对柴油机燃烧噪声影响的试验研究

就不同的喷油控制参数对电控共轨柴油机燃烧噪声的影响进行了研究,柴油机在标定工况运行,通过改变喷油提前角、预喷油量和预喷与主喷时间间隔等控制策略,测量了柴油机顶部1 m处的噪声声压和噪声频谱,探讨燃油系统调整参数对柴油机燃烧噪声的变化规律,结果表明,随着喷油提前角的减小,柴油机噪声先降低再增大,上止点前17°曲轴转角(CA)喷油,噪声声压级最小;合适的预喷油量可以减小柴油机燃烧噪声,预喷油量过大或者过小都不利于燃烧噪声的控制;预喷与主喷时间间隔对燃烧噪声存在影响,时间间隔较小,燃烧噪声较大;预喷与主喷时间间隔较大时,主喷滞燃期增大,缸内压力升高率峰值增大,燃烧噪声升高。     

增压直喷汽油机燃油喷射特性对排放影响的试验研究

基于某1.5L涡轮增压直喷汽油机,搭建试验测试系统,采用试验匹配测试方法研究了喷油模式、喷油时刻、喷油比例、喷油压力等决定燃油喷射特性的关键参数对碳烟排放的影响。试验结果表明:单次喷油模式下在部分负荷时,喷油越提前,碳烟排放越多;在全负荷时,喷油越推迟,碳烟排放越多。在多次喷油模式下,随第一次喷油的推迟碳烟排放降低,随第二、三次喷油的推迟碳烟排放增加。提高喷油压力对部分负荷工况燃烧及排放改善不明显,但外特性工况碳烟排放显著下降,碳氢化合物排放总量也大幅度降低,缸内燃烧速度加快,燃烧稳定性提高,有效燃油消耗率降低约2%。     

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.