二级可调增压柴油机高海拔瞬态特性仿真

为改善车用柴油机高海拔下瞬态工况涡轮迟滞、进气流量响应慢及油耗和碳烟排放增加等问题,利用GTPower建立高海拔单可变截面增压(VGT)二级可调增压柴油机仿真模型,研究了0、3.5和5.5 km海拔下等速加载和恒载加速两种瞬态工况VGT叶片的调节特性,比较VGT叶片3种控制策略对柴油机瞬态特性的影响.结果表明:等速加载工况下,VGT最优控制策略为加载初期保持VGT叶片开度不变至加载中段,之后开度线性增加至加载后稳态工况对应开度;恒载加速工况下,加速初期开始增大VGT叶片开度,至加载中段开度增加至最大转速对应开度,之后VGT开度保持不变持续至加速结束的调节策略加速性能最好.二级可调增压柴油机高海拔加载、加速性能明显优于原机,5.5 km海拔加载过程转矩平均提高了6.2%,加速过程达到最终稳定转速时间缩短了44.8%,体现了二级可调增压系统改善柴油机瞬态特性的优越性.     

增压直喷柴油机瞬态工况燃烧参数的变化规律

为了研究车用增压柴油机瞬态工况下燃烧参数的变化规律,利用燃烧分析仪在试验台上研究了恒转速变转矩瞬态工况下,油门开度变化率对燃烧参数的影响规律。试验研究了该柴油机在1 000 r/min转速下,油门开度分别在5 s、10 s和15 s内由10%匀速增加到90%时柴油机的响应特性和燃烧参数的变化规律。试验结果表明:发动机存在转矩的增加相对于供油滞后的现象,且随着转矩变化率的增加,这种滞后更加明显;在同一转速增转矩工况中,随着负荷的增加,着火滞燃期缩短,最大放热率降低且前移,放热率重心前移;在油门开度相同的情况下,随着转矩变化率的增加,最高燃烧压力下降、最高燃烧压力点前移、着火滞燃期延长、燃烧持续期缩短、最大放热率降低且后移、放热率重心前移、最高燃烧温度下降。     

增压柴油机EGR阶跃工况瞬态响应特性仿真分析

建立了带EGR回路的增压柴油机瞬态仿真平台并验证了准确性.为了缩短EGR阶跃工况的响应时间,进行了EGR阀开度阶跃时间、开阀特性、目标EGR率等影响因素的不同控制策略的对比.结果表明,缩短EGR阀开度阶跃时间,采用“上抛型”开阀控制策略,可改善EGR流量等参数的瞬态响应特性,但会造成转矩波动增加.为减少转矩波动,提出了...     

基于智能滤波的柴油机电子油门控制策略研究

基于GD-1高压共轨柴油机,首先分析了油门抖动对车辆实际运行燃油经济性的影响,结果表明油门的滤波可一定程度改善燃油经济性;然后针对一阶低通滤波算法的缺陷提出了适应于驾驶工况要求的智能滤波的电子油门控制策略;最后在GD-1高压共轨柴油机上成功实现了该控制策略。仿真结果表明:控制策略实现了对电子油门的有效滤波控制,完全兼顾了电子油门的灵敏度和平稳度,小油门的波动幅度小于1%,0至100%的全油门急加速工况油门响应时间小于10个仿真循环,最大限度地发挥出电子油门的优越性能。     

可变增量的EGR控制策略对柴油机瞬态排放的影响

针对涡轮增压柴油发动机在瞬态工况下因涡轮延迟现象所导致的碳氢化合物(THC)和颗粒物(PM)排放相对较高的问题,研究瞬态工况下废气再循环(EGR)变化率与发动机动力性能和排放性能之间的变化规律,搭建基于AVLPUMA系统的柴油发动机瞬态排放测试平台,监测瞬态工况下EGR变化率、进气质量流量与NOx、PM和THC排放物之间的变化关系,在此基础上提出一种可变增量的EGR控制策略.结果表明:通过该策略能够快速有效地降低发动机的喷油量,提高新鲜空气进入气缸的质量流量,提高瞬态空燃比,改善燃烧,最大程度地降低涡轮延迟现象对发动机造成的不利影响;在试验工况条件下,使用该策略可使累计颗粒物排放最高降低83.5%,.     

满足国Ⅳ排放的重型柴油机控制策略设计优化

以某重型车用柴油机为研究对象,针对瞬态测试循环(ETC)工况,通过对轨压控制精度、小油门响应和烟度限制等设计优化,提高轨压控制平稳性、系统响应快速性及改善排放性能。试验结果表明:轨压控制精确性得到了提高,在ETC循环部分工况点,样机每秒轨压降减小了42.1%,小油门踏板开度响应速度增加了27.1%,平均消光烟度值降低了72%。最终样机通过了国Ⅳ阶段ETC排放测试,其中NOx排放裕度为27.7%,颗粒物(PM)排放裕度达到了46.7%。     

柴油机瞬态特性的台架模拟

设计了符合柴油发动机实际运行时的台架试验模型,分析了台架对发动机转速和扭矩的控制原理,进行了不同油门变化率下瞬态性能试验.试验结果表明:油门稳态变化下负荷能够线性增加,油气混合均匀,燃烧良好.油门不同变化率下,负荷都不同程度地出现了二次增加,且两次增加斜率不同,这验证了油气混合不均而引起燃烧恶化;油门变化率越大,由油气混合不均而引起的燃烧恶化越剧烈.     

共轨柴油机控制策略研究

在高压共轨系统开发完成并实现与柴油机的初步匹配后 ,在共轨柴油机上基于自主开发的 3 2位ECU进行了控制策略的深入研究 ;深入分析了高压共轨柴油机在正常运行工况、起动工况、加速工况和汽车下坡工况下的喷油控制策略以及轨压控制策略 ,并通过试验验证。为解决低速全油门扭矩和自由加速烟度的矛盾 ,提出了加速工况的“柔性油门”。匹配后的EQB2 3 1共轨柴油机性能和油耗优于原机 ,排放达到欧 2标准。     

某型16V发电用柴油机突加突卸试验研究

利用改进的比例积分微分(PID)控制策略,完成了100%负荷突卸和52.5%负荷突加的试验指标要求,并给出了柴油机在负荷突变过程中的动态调速特性曲线。为实现60%负荷突加试验的要求,通过优化PID油量表格和喷油正时,同时引入分段喷油策略,使该机突加性能改善明显,瞬态调速率降至6.5%,也为今后改善发电用柴油机突加突卸性能提供了理论依据。     

无回油喷油器高压共轨式电控柴油机轨压控制策略

基于高压共轨电控柴油机无回油喷油器轨压控制,分析了柴油机在负荷突增、突降及轨压跟随性控制困难的原因,并在高压共轨电控燃油喷射系统的基础上,通过在共轨管上增加1个自制的PVC阀,在ECU上增加一路控制通道,设计了柴油机轨压的控制策略,分别对负荷突增、突降及反复加大、减小油门进行试验,结果表明采用柴油机轨压的控制策略可有效改善柴油机轨压控制。     

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.