基于概率统计的发动机停机位置影响因素试验研究

通过大量停机试验,研究不同影响因素下发动机停机时刻曲轴位置的分布规律,并对数据进行概率统计分析,研究停机过程节气门开度、发动机转速等参数对停机位置分布的影响.试验数据分析表明:停机过程中节气门开度对停机位置的分布具有显著影响,节气门开度从0开始逐渐增大,停机位置分布更加趋于集中在压缩冲程的中间区间即上止点前曲轴转角为6...     

LPG单一燃料电控发动机冷起动控制的研究

根据LPG发动机冷起动的特点，设计了LPG发动机冷起动控制策略，在4缸直列单一LPG气态进气道多点顺序喷射发动机上进行了9℃、15℃和20℃的冷起动试验研究。试验结果表明：通过优化初始燃油喷射脉宽、起动喷射脉宽衰减梯度、初始节气门开度、节气门开度衰减梯度等控制参数，可以实现LPG发动机燃烧稳定、起动可靠，并尽可能缩短浓混合气供给时间；为保证可靠起动，LPG发动机和汽油发动机在起动阶段都需要浓混合气，但相对于汽油机，温度对LPG发动机能够成功起动的初始喷气脉宽的影响不是很明显，使用LPG燃料可以缩短起动阶段提供浓混合气的时间，起动过程中为产生相同的转矩，LPG发动机需要较大节气门开度。     

起动初始条件对GDI汽油机反转直接起动模式实现的影响

针对一台4G15缸内直喷汽油机试验研究了冷却水温、活塞初始位置、油轨内燃油压力等起动初始条件对反转直接起动模式实现的影响,并分析了在不同初始条件下膨胀缸和压缩缸控制参数的优化选取策略。研究结果表明:随着初始条件的变化,与之相匹配的优化控制参数也有所改变。燃油压力和冷却水温降低后,需采用较浓的混合气。冷却水温在70~80℃之间时有利于反转起动模式的实现,提高燃油压力同样也有利于反转起动模式的实现。为使反转直接起动模式成功实现,活塞初始位置需要控制在适当的范围内,当压缩缸活塞初始位置处于上止点后曲轴转角为-60°~70°之间时,在压缩缸和膨胀缸相继着火后可使发动机获得较大的正向转动速度,有利于提高起动响应性。     

喷油脉宽和节气门开度对直线发动机性能的仿真研究

基于直线发动机实验台架,建立了直线发动机的GT-Power仿真模型,并进行直线发动机样机实验,将实验数据与仿真结果进行对比,验证了仿真模型的正确性.基于验证的仿真模型,研究了直线发动机的燃烧特性,分析了各主要设计、控制参数对发动机起动性能的影响.结果表明:在节气门开度不变的情况下,喷油脉宽的大小直接影响发动机气缸内的缸压曲线,且随着喷油脉宽的增大缸内压力也不断增大;当喷油脉宽不变,节气门开度在10°～ 60°的范围内变化时,随着节气门开度的增大,直线发动机的缸内压力逐渐降低.     

基于混合动力起动模式发动机起动过程HC排放试验研究

针对ISG型混合动力汽车发动机起动过程中HC排放问题,试验中采用了混合动力起动模式,研究了不同电机拖转转速和不同的冷却液温度条件下发动机起动过程HC的排放控制.不同的ISG电机拖转转速影响缸内混合气的混合与燃烧,合适的拖转转速可以减少HC的排放.试验证明:在常温起动阶段,发动机HC排放性能最佳电机拖转转速为1200r·min-1.试验分析了不同冷却液温度下起动过程HC生成的机理,为HC排放的优化控制提供了理论依据.     

并联混合动力汽车发动机低温冷起动过程分析

通过对并联混合动力汽车发动机进行冷起动试验,研究了超级电容、ISG电机和发动机在冷起动条件下的性能,同时分析了混合动力汽车发动机的冷起动过程.利用冲击起动,发动机在ISG电机的拖动下,克服冷起动初期的摩擦力矩,达到了理想的点火转速,减少了冷起动持续时间,优化了发动机冷起动性能.     

用PLIF测量GDI发动机滚流平面的混合气浓度

通过一台全透明石英气缸套的汽油缸内直喷光学发动机,利用平面激光诱导荧光法(PLIF)定量测量了发动机滚流平面内的混合气浓度分布.在不同节气门开度及不同喷射策略下研究了缸内混合气分布随曲轴转角的变化,讨论了气流运动强弱、喷射时刻及喷射量对发动机混合气的影响;针对可视区域的平均及局部燃空当量比提出了评价不均匀度,并开展了循环变动分析.结果表明:节气门开度不为0时,单次早喷策略均可在上止点附近形成不均匀度评价指标小于0.14的混合气,且不均匀度随进气流动增强而下降;推迟喷射时,油气混合速度明显加快,单次晚喷及双喷工况在上止点附近均可形成不均匀度评价指标小于0.15的混合气;单次早喷、非怠速工况的平均燃空当量比在上止点附近的循环变动小于0.06,而大部分单次晚喷及双喷工况均大于0.13;局部燃空当量比循环变动较大的区域通常为混合气云团运动方向的前沿,较弱的进气流动及推迟喷射会提高整个有效区域内的循环变动.     

曲轴偏置式三缸机的平衡性理论分析与研究

为研究曲轴偏置式发动机的平衡性,应用数学几何理论推导并改进了传统曲轴偏置式发动机曲柄连杆机构的运动学解析方程。基于改进的解析方程对偏置式三缸发动机的平衡性进行分析研究,推导出应用单轴平衡与曲轴过量平衡方法完全平衡一阶往复惯性力矩的平衡轴与平衡重布置相位计算公式;应用虚拟样机技术,对采用同一套曲柄连杆活塞组的偏置式三缸机和对心式发动机的平衡性进行对比分析验证。研究结果表明:曲轴偏置未改变三缸发动机平衡性但平衡相位发生了改变,改进的平衡理论可以准确描述曲轴偏置发动机运动规律,新的平衡方法可以实现一阶惯性力矩的全平衡,相比传统平衡方案提高了剩余往复惯性力矩幅值的均匀性,最大幅值减小约14.5%。     

用于控制的发动机转矩估计方法研究

有一定精度和实时性的发动机动态转矩估计模型,对机电混合电动汽车动力及传动系统控制有重要意义.对发动机动态特性的影响因素进行了分析;分析了平均值模型的优缺点,针对混合动力控制和建模仿真的需要,对模型进行了有效的简化,大大提高了模型的实用性;分析了混合动力中发动机的特定动态工况,建立了特定动态工况下的发动机神经网络模型;基于发动机稳态和动态试验数据,对平均值模型和神经网络模型进行了实证研究.结果表明,基于神经网络的简化平均值模型适用于发动机稳态工况和节气门开度变化率不大的动态工况;神经网络模型适用于发动机稳态工况和特定的动态工况.     

混合动力汽车发动机转速控制策略研究

为消除混合动力汽车发动机运转过程中的转速振荡，利用发动机转速-节气门开度-扭矩对应关系，采用PID控制器调整发动机转速波动。同时，对低负荷发电工况、换档过程发动机转速调整工况下混合动力汽车发动机转速控制策略进行了研究。试验表明上述工况中没有较大振荡产生，发动机转速响应迅速，能够满足整车设计的需要，并为同类研究提供参考。     

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.     

Contents in Volume 23,2014

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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%.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

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.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

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.