"Bump燃烧室"内新概念稀扩散燃烧混合气形成机理的研究

基于自行研制的实验装置,用片状激光诱导荧光法(PLIF)对普通商用柴油喷雾的撞壁混合过程进行了实验研究,并用CFD数值分析软件对其进行了模拟计算,二者结果基本吻合．平板和实际燃烧室的实验及计算结果均表明,撞壁射流在遇到限流沿(Bump)后会剥离壁面,形成二次空间射流,扩大撞壁射流与空气的空间混合体积及混合速率,出现与周围空气迅速混合的“闪混”现象,减少壁面燃油堆积量．计算结果还表明,Bump的存在改变了缸内气流运动的流场结构,Bump附近旋向相反的“双涡结构”极大地增强了二次空间射流对周围空气的卷吸,促进了燃油与空气的混合,是Bump燃烧室内稀混合气形成及稀扩散燃烧的关键所在．     

限流沿燃烧室中实现柴油喷雾稀扩散燃烧的混合气形成过程

提出了一种在于激光诱导荧光法的实验方案，采用增压式共轨喷油器，在定容燃烧实验装置内进行柴油喷雾形成、发展、撞壁和混合过程的实验。实验发现，燃油喷雾在燃料室壁面的沉积可通过在壁面设置一个“限流沿”（BUMP），使之从壁面剥离，剥离后的壁面射流形成一个迅速扩散的二次空间射流，进而形成较均匀、较稀薄的混合气，它有利于减少碳烟和NOx排放。     

有限流沿燃烧室内喷雾撞壁过程的数值研究

作者应用STAR—CD软件对有限流沿燃烧室内喷雾撞壁过程进行了数值研究，发现在活塞接近上止点时，因为缸内温度较高，所以在喷雾到达燃烧室壁面时，大部分液滴已经蒸发，这样基本上没有液滴与壁面的相互作用，所以撞壁模型的选取对计算结果的影响不大。同时也验证了限流沿可以使燃油从壁面剥离。     

“BUMP燃烧室”内混合气形成的多维数值研究

用CFD多维数值分析软件对BUMP燃烧室内柴油喷雾的撞壁混合过程进行了模拟计算,并与用PLIF法取得的试验结果进行了对比,二者基本吻合。试验和模拟计算结果均表明,撞壁射流在遇到BUMP后会剥离燃烧室壁面,形成二次空间射流,扩大撞壁射流与空气的空间混合体积及混合速率,出现与周围空气迅速混合的闪混现象,燃烧室壁面燃油堆积量下降。计算结果还表明,BUMP的位置、高度、形状和角度不同对形成二次空间射流及稀混合气的作用也不相同,在实际应用中应对其进行优化和合理匹配,以便降低柴油机的NOx和碳烟排放。     

温度及压力对柴油机燃烧室内混合气形成影响的数值模拟

用CFD分析软件对柴油机燃烧室内不同环境条件下柴油喷雾的混合气形成及撞壁混合过程进行了模拟计算，并与PLIF法取得的试验结果进行了对比，二者基本吻合．试验和模拟计算结果均表明，油束撞壁后主要沿燃烧室壁面向下移动，在燃烧室近壁区形成一层薄而浓、面积较大的混合气层，且随燃烧室内气体密度的增大，对应时刻及位置的速度、喷雾贯穿距、燃烧室壁面的燃油堆积量、近壁区浓混合气层的面积及混合气浓度减小．     

撞壁距离对柴油喷雾特性的影响

利用复合激光诱导荧光(PLIEF)技术,通过高温高压定容燃烧弹研究了撞壁距离对柴油喷雾撞击平板后的燃油分布影响.试验中,撞壁距离从12.5 mm变化到32.5 mm.结果表明:撞壁距离对燃油分布有重要影响,随着撞壁距离的增加,液相燃油质量分数增加,过浓区间(φ2)的气相燃油质量分数减小,较浓区间(1φ≤2)的气相燃油质量分数增加到一定数量并保持变化不大,稀混合气区间(0φ≤1)的气相燃油质量分数逐渐增加;瞬态最大当量比(φmax)降低;瞬态最低温度(Tmin)发展趋势与φmax相反;气/液相喷雾壁面射流半径和高度大幅减小,甚至不与壁面相撞.     

柴油喷雾撞壁形态和油束发展特征

在一台高温、高压定容燃烧弹上研究了不同撞壁距离、喷射压力和环境温度与压力条件下,柴油油束撞壁后近壁面区域的喷雾特性.利用高速摄像测量了自由喷雾和撞壁喷雾的油束发展历程,并结合仿真对燃油气相浓度和流场特性进行分析.结果表明:在环境温度为500~900,K、环境压力为1~4,MPa时,喷射压力对喷雾锥角影响较小;环境温度达到700,K及以上时,喷射压力对喷雾贯穿距的影响较小,特别当撞壁距离减小到30,mm和20,mm时,出现喷雾贯穿距随喷射压力增大而略微减小的趋势;相对于撞壁喷雾,环境温度对自由喷雾贯穿距的影响更大;随着撞壁距离减小,喷雾贯穿距逐渐减小,喷雾锥角逐渐增大,而喷雾高度则呈现先增大后减小的趋势.在上述4种边界参数中,撞壁距离对撞壁油束发展特征影响最大.     

燃烧室壁面形状对撞壁射流气体混合过程的影响

本文研究了燃烧室壁面形状对撞壁射流气体沿壁发展过程的影响，实验发现：射流气体撞壁后主要沿壁面发展；近壁区域会形成浓混合气层，并且混合很慢，本文提出了两种方法，１）在壁面设置矩形凹槽，并且利用环境的气流运动加快射流气体的混合。２）在壁面上设置条形障碍物，使射流气体脱离壁面形成空间流动，另外，本文也模拟了ＯＳＫＡ－Ｄ燃烧系统中燃油撞壁后的发展过程。     

撞击平板壁面的柴油喷雾的燃油分布研究

利用复合激光诱导荧光(PLIEF)技术,在一个高温高压定容弹内研究了柴油喷雾撞击平板后的燃油分布。研究结果表明:撞壁对燃油分布有重要影响。撞壁喷雾可以分为:(1)气液相喷雾同时撞壁,在近壁面形成近壁浓区,瞬时最大燃空当量比(Φmax)和最低温度(Tmin)存在于撞壁点附近;(2)气相喷雾撞壁液相喷雾不撞壁,近壁面当量比相对较高,Φmax和Tmin存在于撞壁点上方的自由射流段中;(3)气液相喷雾都不与壁面接触,相当于自由喷射。随着撞壁距离的增加,液相燃油质量分数增加,Φ2的过浓区间的气相燃油质量分数减小,1Φ≤2的较浓区间的气相燃油质量分数增加到一定数量并保持变化不大,0Φ≤1的稀混合气区间的气相燃油质量分数逐渐增加。     

BUMP燃烧室内柴油喷雾气液相缸内浓度场测量激光诱导荧光法的实现和研究

本文应用复合激光诱导荧光（Planar Laser Induced Exciplex Fluorescence）测试技术,实现了对BUMP燃烧室内柴油喷雾的气液相浓度分布同时进行测量的光学测试系统,并研究了改变BUMP燃烧室形状和二次撞壁距离对喷雾气液相浓度场分布的影响情况。研究发现,BUMP燃烧室形状对喷雾缸内分布有明显作用,合适的BUMP高度能够剥离撞壁喷雾,形成二次射流,加速喷雾在燃烧室内与空气的混合,研究中缩口角度14°,BUMP高度1.5mm的BUMP燃烧室具有研究中最理想的喷雾气液相缸内分布。     

Contents in Volume 23,2014

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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.     

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.