气体机点火时刻和燃料当量比对气耗影响的研究

研究了天然气(LNG)发动机点火提前角与燃料当量比对燃料消耗率的综合影响,对点火过程的各阶段进行了分析,对不同当量比的混合气燃烧过程进行了对比,通过改变点火提前角和燃料当量比,得到不同工况下发动机的点火提前特性和燃料调整特性,本次试验数据表明:在各工况下,要获得最低的燃料消耗率,点火提前角与燃料当量比均存在一个最佳值,选择较合适的点火提前角与燃料当量比,使天然气发动机可以兼顾低速动力性与高速经济性。     

稀燃天然气掺氢发动机的热效率与排放特性

为了分析在天然气中掺入不同体积比的氢气对发动机经济性和排放性的影响,在一台6缸火花点火天然气发动机上开展了体积掺氢比在不同工况下对热效率和排放特性影响的试验研究.结果显示掺氢可以拓宽发动机的稀燃极限,提高燃烧速度,使得最佳转矩点火提前角(MBT)相对推迟;在点火提前角不变的情况下掺氢对热效率没有明显优势,而且会使NOx排放升高.而在MBT时,掺氢可以一定程度上提高发动机的指示热效率,降低未燃CH4和CO的排放,改善NOx与未燃碳氢(主要为CH4)的trade-off关系.掺氢的优势还体现在可以让发动机高效的工作在更稀的情况下,从而有利于降低NOx的排放和传热损失.     

在稳定性指标制约下汽油机应用稀燃和EGR的局限性

本文应用微机检测发动机稳定性指标,在一台采用涡流室火花塞组成快速燃烧系统的汽油机中,对影响燃油消耗率、NO_x排放和稳定性指标的主要参数如空燃比、点火提前角和废气再循环率进行了试验研究。结果进一步表明:在稳定性指标制约条件下,稀燃能节油,但不能降低NO_x排放;EGR能降低NO_x排放,但不能节油。     

纯氢和天然气掺氢燃料发动机的试验研究

在某点燃式发动机上,试验研究了纯氢和不同比例天然气掺氢的燃烧与排放特性。结果表明：纯氢燃料燃烧快,燃烧持续期短,缸压和放热率升高率大且峰值较高,λ=1．1时,峰值压力为3．9MPa,燃烧持续期为12℃A。氢燃料的稀燃界限宽,过量空气系数λ=3时,峰值压力降低到1．7MPa,NOx排放趋于零。天然气掺氢可以改善天然气燃烧特性,拓展天然气的稀燃极限。在相同工况下,掺氢30％的混合气燃烧持续期比天然气缩短20℃A,但缸压峰值和NOx排放增加,这可以通过稀燃和优化点火提前角来降低峰值压力和NOx排放。掺氢30％的混合气可以在λ=1．857时稳定的工作,此时峰值压力降低到1．57MPa,NOx的排放小于50×10^-6。     

不同点火提前角时HCNG发动机的燃烧与排放特性

在一台火花点火天然气发动机上开展了在不同点火提前角下燃用不同体积掺氢比(O%～50%)的天然气掺氢燃料(HCNG)的试验研究,进行热效率、燃烧放热率、循环变动及排放特性的分析.结果表明:与原天然气发动机相比,HCNG发动机的最大扭矩点火提前角(MB了)减小,MBT时指示热效率变化不大;点火提前角增大时,火焰发展期增长,最大压力变动率减小,快速燃烧期和平均指示压力变动率先减小后增大;在相同点火提前角时,以上4个参数均随掺氢比的增加而减小.N0x、CO排放浓度随掺氢比增加而增大,CH4排放則相反.     

增压稀燃天然气发动机排放特性

为了研究增压稀燃天然气发动机的排放特性,对发动机进行了空燃比和点火提前角调整试验、十三工况排放等试验,并在增加氧化型催化转化器后进行了相关试验,对试验结果进行研究分析,获得了天然气发动机的排放规律.结果表明:NMHC排放随空燃比增大先减少后增加,NOx排放随空燃比增大先增加后减少,在空燃比19～21左右达到最大值.NMHC比排放随转速升高略有降低,NOx排放随转速升高先减小后增加,发动机最低NOx排放点所对应的发动机转速为1600～1800 r/min.定MAP下,NMHC排放随点火提前角增大先降低后增加,NOx排放随点火提前角增大而增大.加Ⅰ型氧化催化器后发动机NOx、CH4、CO、NMHC排放值分别减少了15%、97%、78%、60%.试验结果表明,增压稀燃和氧化型催化转化器相结合是天然气发动机一种有效方案.     

重型增压预混天然气发动机动力性和排放性试验研究

为解决天然气发动机排放问题,对严重影响天然气发动机HC和NOx排放的空燃比和点火提前角这两个参数进行试验研究。结果表明,增大点火提前角可以提高发动机功率输出,降低有效燃气消耗率和HC排放,增加NOx排放;增大空燃比,发动机功率和NOx排放下降,而有效燃气消耗率和HC排放上升,且均在稀燃极限空燃比时急剧变化。     

点火正时对甲醇汽油发动机排放的影响

以吉利MR479Q汽油机为试验对象,采用AVL SESAM FTIR多组分气体分析仪和DEWETRON-CA燃烧分析仪,对典型稳态工况下汽油机燃用不同掺混比例甲醇汽油时的常规和非常规排放点火正时调整特性进行了试验和分析.汽油机燃用甲醇汽油后转矩有增大趋势,相同工况最大转矩对应最小点火提前角(MBT)随甲醇掺混比例增大而减小.甲醇汽油不改变汽油机常规排放变化规律,但因燃烧过程改善,绝对排放量显著降低.非常规排放随甲醇掺混比例升高显著增大,甲醇体积分数为80%,(M 80)时未燃CH_3OH排放达0.9×10-3以上,CH_2O排放达0.25×10-3以上.相同甲醇汽油下,未燃CH_3OH排放随点火提前角增大而升高,CH_2O随点火提前角增大有所降低.     

不同点火时刻下天然气掺氢缸内直喷发动机燃烧与排放特性

在缸内直喷火花点火发动机上开展了天然气掺混0％-18％氢气的混合燃料不同点火时刻下的试验研究。结果表明：对于给定的喷射时刻和喷射持续期,点火时刻对发动机性能、燃烧和排放有较大影响,喷射结束时刻与点火时刻的间隔对直喷天然气发动机极为重要,喷射结束时刻与点火时刻的间隔缩短时,混合气分层程度高,燃烧速率快,热效率高。最大放热率等燃烧特征参数随点火时刻的提前而增加。HC排放随点火时刻的提前而下降,CO2和NOx排放随点火时刻的提前而增加,NOx排放的增加在大点火提前角下更明显。掺氢可降低HC排放,对CO和CO2排放影响不大。掺氢量大于10％时可提高天然气发动机热效率。     

空气辅助喷射甲醇发动机燃烧特性试验研究

为了优化低负荷下甲醇发动机的燃烧及性能,将空气辅助喷射系统应用于甲醇发动机,并研究了喷气时刻、点火提前角和喷气脉宽对甲醇发动机燃烧特性的影响,结果表明：推迟喷气时刻至进气门开启之后有利于加快燃烧速度,提高发动机燃烧稳定性,尤其是在稀薄燃烧时的影响更明显,最佳的喷气时刻为300°CA BTDC．增大点火提前角可以缩短发动机的急燃期,提高燃烧稳定性,但是当喷气时刻推迟时,为了获得更好的动力性,最佳点火提前角也要推迟．增大喷气脉宽能优化发动机燃烧质量,提升发动机动力性和稳定性,但是当喷气时刻较早(闭阀喷射)或过晚时,喷气脉宽大于4 ms后动力性和燃烧稳定性增加不明显．并且在喷气时刻300°CA BTDC、喷气脉宽7 ms时,发动机的动力性和燃烧稳定性达到最佳．     

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.