喷油策略对离子电流信号与HCCI燃烧相位相关性的影响

在一台进气辅助加热的缸内直喷HCCI汽油机上,研究了喷油策略对HCCI燃烧离子电流信号与HCCI燃烧相位之间相关性的影响.结果表明:喷油时刻推迟时,缸压和离子电流峰值均减小,燃烧和离子电流特征值相位亦推后;喷油量增加时,缸压和离子电流峰值增大,燃烧和离子电流特征值相位提前;最大燃烧放热率时的曲轴转角dQmax与离子电流差分最小值相位dImin的相关性最高,50%累积放热量对应的曲轴转角CA50与离子电流信号最小值相位Imin次之,10%累积放热量对应的曲轴转角CA10与离子电流起始点相位Ist最低,即使在爆震燃烧发生时,dQmax与dImin依然具有较高的相关性;喷油时刻对离子电流与燃烧相位的相关性影响不大;与二次喷油量相比,首次喷油量的调整对离子电流与燃烧相位的相关性影响更加明显;可通过调整首次喷油量进行基于离子电流的HCCI燃烧相位的闭环控制.     

工况参数对柴油机离子电流与燃烧相位相关性的影响

通过一台2.0,L柴油机研究了不同EGR率、喷油压力、循环喷油量、转速以及冷却水温等工况参数对柴油机燃烧循环变动及离子电流信号与燃烧相位相关性的影响.结果表明:柴油机燃烧过程产生的离子电流信号特征值与燃烧相位之间的相关系数在不同工况参数下均接近或达到0.8,属于高度相关,可以使用离子电流信号特征值对燃烧相位进行预测;离子电流信号特征值与燃烧相位之间的相关系数受燃烧循环变动的直接影响,降低燃烧循环变动可以有效提高其相关系数.     

可控自燃工况离子电流信号与NO_x排放相关性

基于改造的可控自燃(CAI)发动机试验台架,采用离子电流检测系统与瞬态NOx排放分析仪,结合Chemkin-Pro软件的化学反应燃烧数值模拟,研究了可控自燃工况下离子电流与对应循环NOx排放之间的相关性.结果表明:采用不同燃料的CAI燃烧过程中,离子电流信号强度与对应循环NOx排放呈现较为明显的正相关性,且缸内离子产物出现时刻相比NOx较早,使离子体积分数峰值时刻与NOx体积分数达到最大值的时刻之间出现了相位差.由此发现,在离子电流信号质量稳定时,综合离子电流信号强度与离子电流峰值相位的信息,能够实现循环内的NOx排放估测与反馈,为循环内的燃烧优化及后处理系统精确控制提供了参考依据.     

基于离子电流的缸内直喷汽油机HCCI燃烧检测研究

在缸内直喷汽油机上,对基于离子电流的HCCI燃烧检测方法进行了研究.结果表明,直喷方式下,离子电流信号受背景噪声影响,信噪比较低.当过量空气系数φa＜1.6时,信号特征值与燃烧相位线性对应关系良好;但φa继续增加时,信号幅值大幅减弱,二者线性相关系数显著降低.喷油策略也会对燃烧相位检测结果造成影响,在相同过量空气系数下...     

SI/HCCI双燃烧模式汽油机火花塞离子电流检测装置的研究

为了研究离子电流信号在HCCI燃烧负荷拓展控制中的应用,研制了一套用于SI/HCCI双燃烧模式下离子电流检测装置,检测出两种模式下的离子电流信号,取得了满意的效果。研究表明离子电流信号能够良好地指示实际燃烧过程,如燃烧定时、非正常燃烧等,可为HCCI燃烧控制提供非常重要的信息。     

基于振动信号和瞬时转速信号的HCCI燃烧相位CA10辨识

为了实现基于循环的HCCI燃烧闭环控制,提出了一种基于爆震传感器信号和瞬时转速信号的CA10(缸内燃料燃烧10%累积放热量时的曲轴转角θ10)辨识模型.在装有全可变气门系统的汽油HCCI发动机上,测取HCCI发动机各工况下爆震传感器信号和瞬时转速信号,用时频分析方法从爆震传感器信号及瞬时转速中提取表征振动信号相位信息的特征量和瞬时转速信号特征量,分析了它们和HCCI燃烧相位θ10之间关系,提出了一种计算简单,以爆震传感器和瞬时转速信号特征量为因变量的CA10辨识模型.分析表明,CA10辨识模型能比较准确地识别HCCI燃烧相位的θ10值,对于HCCI动态过程燃烧相位θ10的预测平均误差小于1.7,°CA.     

供油参数对柴油机离子电流特性影响的试验

基于一台2.0,L高压共轨柴油机,并结合自行开发的电子控制与信号采集系统,研究了包括不同喷油压力、循环喷油量和喷油时刻在内的共轨供油参数对柴油机离子电流信号特性的影响.结果表明:离子电流幅值与积分值随喷油压力、循环喷油量的提高与喷油时刻的提前而增大.在不同的共轨供油参数下,离子电流相位总是滞后于燃烧相位,但离子电流相位与燃烧相位的变化规律一致,证明了离子电流信号相位表征燃烧相位的可行性.     

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。     

臭氧对天然气HCCI发动机燃烧影响的数值研究

HCCI(均质充量压燃)发动机的燃烧过程主要是受到燃料本身的化学反应动力学控制,因此改变燃料的化学性质能够有效地控制HCCI发动机的燃烧过程。由于天然气不易压燃的化学特性,所以天然气HCCI发动机低负荷运行时,会因燃烧反应速率过慢而出现火焰温度低、燃烧不充分甚至"失火"等现象。本研究中,通过耦合详细介绍天然气和臭氧(O3)的燃烧反应机理,并结合HCCI单区模型,模拟计算了进气道添加O3对天然气HCCI发动机燃烧相位的影响并进行化学反应路径分析。通过模拟计算与试验结果对比得出:进气道中添加10~40 ppm的O3可以改变天然气的燃烧反应路径,实现对天然气HCCI发动机燃烧相位的控制。低浓度的O3能有效地改变天然气低温燃烧时的燃烧相位并提高缸内燃烧压力,拓宽天然气HCCI发动机低负荷工况范围。     

汽油HCCI发动机燃烧相位及瞬态过程的控制

由于HCCI燃烧受化学动力学控制,燃烧相位控制一直是HCCI面临的挑战之一.通过缸内直喷方式,可以灵活控制HCCI燃烧相位.研究表明,在HCCI失火界限,在负气门重叠期喷入燃油,能够实现燃油重整,通过调整不同的负气门重叠喷油量,可以控制燃烧相位;在HCCI爆震界限,负气门重叠期的喷油会导致燃烧粗暴,NOx排放大量上升,而在压缩行程喷入燃油形成分层混合气,能够有效地控制燃烧相位,且不引起排放的恶化.通过负气门重叠喷油形成的组分控制和压缩行程喷油形成的浓度控制相结合,能够在整个HCCI运行范围内有效地控制燃烧相位.通过考察燃烧相位调整的瞬态过程,发现通过缸内直喷技术,能够在一个发动机循环内实现燃烧相位的调整,控制灵活,响应迅速.     

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.     

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.     

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。     

Contents in Volume 23,2014

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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.