排气道隔热方式对气缸盖整体温度场影响的研究

本文对BF8L413F风冷柴油机气缸盖排气道采用的两种隔热方式——喷涂1.5mm氧化锆陶瓷涂层和1mm空气层隔热的隔热效果进行了研究。用ANSYS程序对原机和两种隔热方式的气缸盖温度场和热流场进行了数值模拟。计算模型和实际气缸盖结构基本一致,各部分形状、特别是排气道的结构形式没有作任何简化。数值模拟与实验结果吻和很好。研究表明排气道隔热可有效降低缸盖整体的热负荷,而空气层的隔热效果比陶瓷涂层的隔热效果更为明显。     

排气道隔热方式对气缸盖整体温度场影响的研究

本文对BF8L413F风冷柴油机气缸盖排气道采用的两种隔热方式－喷涂1．5mm氧化锆陶瓷涂层和1mm空气层隔热的隔热效果进行了研究。用ANSYS程序对原机和两种隔的热方式的气缸盖温度场和热流场进行了数值模拟。计算模型和实际气缸盖结构基本一致,各部分形状、特别是排气道的结构形式没有作任何筒化。数值模拟与实验结果吻作很好。研究表明：排气道隔热可有效降低缸盖整体的热负荷,而空气层的隔热效果经陶瓷涂层的隔热效果列为明显。     

Al-Fe2O3系反应合成灰铁管陶瓷内衬的隔热性能

主要测试和讨论Al-Fe2O3系SHS-重力分离法制备的陶瓷内衬灰铁管的隔热性能。实验结果表明，在添加剂SiO2的加入量分别为5％，10％，15％时，陶瓷层的厚度分别为1mm，2．1mm，2．5mm，管表面温度分别下降23．6％，32．7％和41．4％。隔热性能随温度的提高而下降，是内衬中的热阻碰撞、点缺陷、晶界散射、位错等因素综合影响的结果。     

降低6160A型机排气系统表面温度

降低６１６０Ａ型机排气系统表面温度张泉（山东潍坊柴油机厂）１前言６１６０Ａ型船用增压柴油机由于结构简单，运行可靠．使用维护方便，而深受用户青睐，成为我国中小型船舶的理想动力，但由于该机的排气系统无有效的隔热保护，因而使用该机的船舶机舱温度较高，使工作...     

柴油机排气道改进对散热量的影响

降低缸盖排气道的散热量能提高发动机热效率和排气温度,以某6缸重型柴油机为研究对象,结合流固耦合计算和一维、三维耦合计算,获得了较为准确的一维热力学模型．在此基础上设计不同表面积和直径的排气道方案,采用一维热力学仿真,计算各方案在多工况下的对流换热系数、散热量和涡前排气温度．结果表明：气侧对流换热系数基本不受气道表面积影响,但会随着气道直径的增大而迅速下降,并与直径的平方呈反比．散热量随着气道表面积减小等比例减小,也会随着直径增大而降低,且降低比例稍低于气侧对流换热系数的降低比例．涡前排气温度随着排气道散热量的降低而升高,A4方案的涡前排气温度最高,表面积减小到60%,标定工况点可以提升22.6℃．     

对气缸盖基本拓扑结构及其气道的参数特性研究

利用参数研究方法,对大功率柴油机气缸盖的基本拓扑结构及其气道的参数特性进行了研究,获得了在纯机械负荷下,气缸盖的底板、顶板、中隔板、缸体丝对立墙、进排气道以及进排气侧壁的总体厚度变化对气缸盖整体应力水平的影响规律。     

基于CFD分析的某轻型卡车发动机舱热保护研究

基于计算流体动力学(computational fluid dynamics, CFD)模拟仿真与热平衡试验,对某轻型卡车的整车温度场进行分析,发现蓄电池、排气歧管与涡轮增压器附近线束的表面温度较高,出现热害现象。根据热害发生位置,对高温部件使用隔热罩削弱热辐射,使蓄电池与线束在热浸状态与发动机最大扭矩(转速为1300 r/min)工况下,温度始终低于其许用最高温度,避免零部件的高温失效甚至自燃;并根据隔热罩厚度与隔热效果的关系,在不影响隔热效果的同时,降低隔热罩厚度,实现轻量化设计。     

发动机气缸盖维修技术要领

缸盖是用来密封发动机机体缸孔的重要部件．与缸套共同形成燃烧室,气缸盖上有很多孔道,分别是水道．承担分配各缸冷却水的分布冷却：油道,是润滑发动机上部零部件的主要通道;气道,分别是进气道和排气道。气缸盖承受着活塞爆炸作功巨大的反冲力的,所以设计这些孔道时要合理分布,注意应力集中,制作过程中还要进行时效处理。     

160系列柴油机讲座(5)

<正> 6 冷却系统 6160A系列柴油机的冷却水循环方式,陆用机和船用机均有开式和闭式两种型式。陆用机的开式冷却系统使用冷却水池贮水,水泵将从冷却水池吸入的冷水泵至主进水管内,冷却机油后进入机体、气缸套周围的冷却水腔,而后经机体顶面水孔进入气缸盖水腔,并从气缸盖排气道顶部的出水孔排至总出水管,最后导至水池中用喷头喷出,(或设置冷却塔),水池的容量应≥25m~3,水泵的吸水高度应≤2m,柴油机的出水温度应为70～75℃左右,为使柴油机受热零件在较稳定的温度下工作,进、出水温度应≤25℃。在环境温度较低时还可利用调节阀在进水中加入部分柴油机排出     

燃气轮机排气扩散段超温治理实施

对西门子SGT5-4000F(4)型燃气轮机排气扩散段的功能和结构进行了简要介绍,重点介绍了燃气轮机排气扩散段超温治理实施方案及效果。通过优化燃气轮机排气扩散段保温固定结构、增加耐高温隔热保温涂层等措施,成功将排气扩散段外表面温度控制在环境温度+25℃合格标准以下。该方案是一次扩散段超温治理的全新探索,所采取的措施也是在同型燃气轮机机组上的创新应用,具有较高的推广价值。     

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.     

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.     

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.     

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.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

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.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法,这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

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。