汽油醇混合燃料发动机冷起动排放特性研究

随着国Ⅲ及以上排放法规的实施,对发动机冷起动过程排放的控制显得越来越重要.在一台3缸进气道喷射汽油机上开展了不同环境温度下醇类汽油混合燃料对冷机起动及其后怠速暖机过程排放特性的研究.研究中设计了一种新颖的排放采样系统,测量了冷起动和暖机过程的HC和CO排放.甲醇汽油与乙醇汽油混合燃料排放对比发现:甲醇汽油具有更加优良的冷起动排放性能.分别在环境温度为5℃、15℃和25℃时进行了甲醇汽油对冷机起动及怠速暖机过程排放特性影响的研究.研究表明:在相同的环境温度下,HC和CO排放随着试验燃油中甲醇添加比例的增加明显降低;甲醇汽油对发动机冷机起动及暖机阶段HC和CO排放的改善在温度较低时表现的更为明显,环境温度为5℃,发动机燃用M30时,HC排放可降低40%,CO可降低70%.     

低比例甲醇汽油发动机冷起动非常规排放和燃烧特性研究

在电控进气道喷射汽油机台架上,分别使用汽油、M10、M20和M30 4种燃油在常温条件下模拟了NEDC测试循环中的前2个市区工况循环(ECE),对冷起动过程中催化剂前后的常规排放和非常规排放以及燃烧特性进行了研究。研究结果表明:随着燃油中甲醇比例的增大,4种燃油的CO、NOx排放量逐步减少,而甲醇、甲醛等非常规排放量逐步增多。THC排放量在冷起动初期随着甲醇比例的增大而增加,在发动机温度上升后随着甲醇比例的增大而减少。但是在常规三效催化剂起燃以后,催化剂后的常规和非常规排放基本上均能得到有效控制。随着汽油燃料中甲醇添加比例的增大,在冷起动过程中发动机燃烧持续期缩短,缸内平均指示压力略有升高,对发动机缸内燃烧有一定的改善作用。     

直喷汽油机二次喷射改善冷起动性能的研究

通过一台直列4缸汽油机分析了喷油模式对直喷汽油(GDI)发动机冷起动过程及冷态怠速过程的影响.结果表明:通过调整喷油策略可以改变缸内混合气的燃烧过程,在二次喷油比例为0.6∶0.4、喷油定时分别为上止点前300°CA和140°CA、环境温度为-30℃条件下,发动机的燃烧特性最佳,HC排放最低.在车辆冷起动过程中,通过二次喷射可以有效缩短混合气的滞燃期和燃烧持续期,以达到缩短起动时间、提高起动性能的目的.在起动后的怠速阶段,采用二次喷射可以大幅提高发动机的燃烧稳定性,有效消除怠速不稳的问题.在闭环控制阶段,通过二次喷射合理组织缸内混合气分布,可以有效改善减稀混合气造成的车辆抖动问题.此外,缸内混合气燃烧过程的优化可以有效降低冷起动过程的HC和CO排放,但会造成NOx排放的小幅升高.     

进气预热降低汽油机冷起动排放的研究

研究了不同进气温度、加热方式和蓄热箱容积对发动机冷起动排放的影响规律。结果表明，提高进气温度有利于减少冷起动阶段的HC、CO排放。最初参与缸内燃烧的新鲜空气的温度对冷起动HC排放有重要影响，对发动机进气歧管内的冷空气进行加热可以大幅度降低HC排放。蓄热箱容积一定时（30L），存在一个进气温度（70℃）可以使HC、CO排放改善得到最佳效果（分别降低36％和13％）。较强的蓄热能力，可以在较大温度范围内减少排放。     

甲醇汽油双燃料发动机的怠速性能试验

在一台加装了甲醇喷射系统的汽油机上,对不同比例甲醇汽油作用下的发动机怠速特性进行了试验.试验过程中将发动机转速及水温分别控制在800,r/min和90,℃左右,调整甲醇和汽油的喷射脉宽使甲醇比例从0%逐渐增加至100%,同时保证混合气的浓度被控制在理论空燃比附近.结果表明:随着甲醇比例的增加,燃烧效率和指示热效率有所上升;缸内混合气的燃烧速度加快,燃烧持续期明显缩短;平均指示压力的循环变动系数逐渐降低;反映缸间差异的曲轴自由端0.5谐次角位移振动幅值降低.HC、CO和NOx排放的平均值也随甲醇比例的增大而明显降低.     

甲醇-柴油混合燃料对发动机燃烧及排放特性的影响

在一台YTR3105直喷式柴油机上进行了小比例甲醇-柴油混合燃料发动机的燃烧及排放特性试验研究。结果表明:在相同的平均有效压力和转速下,随着甲醇含量的增加,燃料着火延迟相应增大,使得燃烧过程向上止点后移动。混合燃料的滞燃期比柴油长,预混燃烧放热率峰值增大,燃烧持续期缩短,缸内最大爆发压力和压力升高率增加。与纯柴油相比,甲醇-柴油混合燃料HC排放有所升高,但NOx和碳烟排放降低。大负荷时,CO排放显著下降。     

甲醇柴油对增压中冷柴油机燃烧与排放性能的影响

针对在增压中冷柴油机上燃用不同比例甲醇柴油对发动机燃烧和排放性能的影响进行了研究。结果表明：随着混合燃料中甲醇含量的增加,发动机动力性略有降低,使用经济性提高,缸内最大压力和温度降低,NOx和碳烟排放降低,HC排放增加;CO排放小负荷下大幅增加而在大负荷下略有降低。     

用汽油和甲醇燃油分层拓展HCCI燃烧高负荷的试验研究

在一台单缸HCCI发动机上研究了进气道喷射汽油缸内喷射甲醇形成汽油甲醇燃油分层的HCCI燃烧排放特性,探索了其拓展HCCI燃烧高负荷的潜力。试验结果表明:在汽油HCCI燃烧中喷射甲醇能够有效降低缸内混合气的温度,推迟着火时刻,延长燃烧持续期,从而降低压力升高率和缸内最高燃烧压力,有利于拓展HCCI燃烧高负荷。一定的HCCI负荷工况存在最佳的汽油甲醇比例,且汽油甲醇最佳比例随着负荷的增加不断减小。在最大压力升高率0.5MPa/°CA和较高的指示效率的限制下,自然吸气条件下采用汽油和甲醇燃油分层的HCCI燃烧最高负荷比汽油HCCI燃烧提高了近50%,达到0.62MPa。     

喷射参数对二甲醚PPCCI发动机燃烧与排放特性的影响

在一台6缸增压电控共轨二甲醚发动机上进行试验,研究了预喷时刻、预喷燃料量、喷射压力、主喷时刻等喷射参数对二甲醚部分预混合充量压缩燃烧(PPCCI)发动机燃烧与排放特性的影响。试验结果表明:随预喷时刻提前,缸内压力峰值降低,二甲醚发动机缸内燃烧由两阶段放热转变为PPCCI三阶段放热,氮氧化物(NOx)排放显著降低,HC和CO排放升高;随预喷射燃料量增加,缸内压力峰值及预混合燃烧的冷焰反应和热焰反应速率明显增大,NOx排放逐渐降低,HC和CO排放显著升高;随喷射压力降低,预混合燃烧热焰反应速率增加,主喷扩散燃烧始点推迟,扩散燃烧放热率峰值和NOx排放明显降低,HC和CO排放升高;随主喷时刻推迟,预喷预混合燃烧几乎没有变化,主喷扩散燃烧延后,缸内压力峰值和放热率峰值降低,NOx排放显著降低,HC和CO排放升高。     

基于缸内直喷的甲醇汽油混合燃料HCCI燃烧排放特性研究

在缸内直喷发动机上研究甲醇汽油混合燃料的HCCI燃烧排放特性,分析了其非常规排放的性能。试验中选用汽油、M10(甲醇体积分数10%)、M20(甲醇体积分数20%)3种燃料,并通过FTIR方法测量甲醇及甲醛等非常规排放。研究结果表明:在汽油中添加甲醇可以有效拓展HCCI燃烧的高负荷范围,M20燃料的高负荷范围比汽油提高近9%,指示燃油消耗率比汽油高5%～10%,但指示能量消耗率比汽油低2%～6%。CO、THC、NOx等常规排放随甲醇添加比例的增加而降低,而甲醇和甲醛等非常规排放随甲醇添加比例的增加而增加,并随负荷增高呈先增加后减少的趋势。     

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.