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。     

钢壳陶瓷喷涂隔热排气道气缸盖单缸试验研究

介绍了单缸增压风冷模拟试验台设计调试过程和气缸盖温度测量方法。采用陶瓷钢壳隔热排气道气缸盖,增大供油量后,发动机功率从２９．４ＫＷ提高至３３．１ｋＷ,其燃油湖水率、排气烟度有所下降,但排气温度约升高２０℃,在相同工况下,隔热排气道内表面温度上升４５℃,但气缸盖外表面温度下降２５℃。     

耐火纤维——空气层绝热结构的效果试验

本文通过介绍国外的“双层炉壳”箱式电阻炉的情况及国内箱式电炉的试验情况,说明了耐火纤维——空气层绝热结构是一种简单、便宜、行之有效的隔热方法。并通过模拟试验情况的介绍,向大家推荐了空气层厚度的较佳数值。     

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。     

柴油机排气道数值模拟和优化设计

使用Fluent软件对不同气门升程的排气道流场进行CFD数值模拟,并将计算结果同试验数据进行对比,发现两种方法获得的流量数据吻合良好。通过对数值模拟结果进行分析,指出了排气道改进的方向,改进后排气道的数值模拟结果显示流量系数获得较大提升。     

气缸盖中一些关键功能结构的承载机理研究

借助有限元和力学等效原理等方法，对气缸盖中的一些关键功能结构的承载机理进行了深人研究。研究结果表明：气缸盖中的喷油器护套、进排气道、气门导管座孔、中隔板和加强筋通过不同的形式，传递并分散了作用在气缸盖上的燃气爆发压力；这些结构对抑止气缸盖的整体变形、降低气缸盖的总体应力集中水平具有重要的作用；调整这些结构的特性参数可以达到对气缸盖整体和局部应力水平的有效调整。     

基于缩孔预测的蠕墨铸铁气缸盖铸造工艺改进

针对蠕墨铸铁气缸盖铸造过程中出现的铸造缩孔缺陷,对气缸盖进行了铸造过程数值仿真及缩孔缺陷预测.结果表明:在铸件凝固过程中,喷油器安装孔位置是金属液的最后凝固位置,缩孔主要出现在喷油器安装孔位置以及远离直浇道一侧的进排气门导管处.缩孔缺陷产生的主要原因是金属液补缩能力不足以及在喷油器安装孔位置金属液的冷却速度过慢.为了防止缩孔缺陷的产生,基于铸造过程的数值模拟结果,对铸造工艺进行了改进,即增大内浇口宽度以及在喷油器安装孔位置安放冷铁.数值模拟与实际浇注表明,改进工艺方案有效地防止了气缸盖内缩孔缺陷的产生,提高了气缸盖铸件的铸造质量.     

某16缸中速柴油机冷却水系统分析与优化

为了分析某柴油机冷却水套冷却性能,用CFX软件对整体冷却水系统进行绝热的三维流动模拟并对冷却效果最差的8#缸进行了气缸盖-冷却水套-气缸套的流固耦合传热仿真,获得了详细的速度场和温度场分布。模拟结果显示整体冷却水套大部分区域流速在0.5m/s以上,进排气门冷却环的流速最大,高温区域主要集中在气缸盖火力面、排气道侧和气缸套中部。在此基础上,提出了冷却水套的三种改进方案并进行比较,结果表明:方案3为最佳优化方案,其平均传热系数比原方案提高了30%以上。     

隔热材料导热系数预测及其在发动机排气管隔热中的应用

由于排气管隔热在特种车辆中的重要性,在对排气管隔热方案分析的基础上,采用大型通用CFD软件STAR-CD,模拟氧化锆空心球隔热材料的导热系数,并对排气管真实的流固耦合模型进行大量的数值模拟试验。数值模拟可以分析隔热结构中隔热材料厚度、表面发射率、隔热方式等因素对排气管隔热效果的影响;通过隔热材料与真空层的匹配,得到既满足紧凑性要求,又能高效隔热的排气管隔热方案。     

高温服役过程热障涂层隔热性能演变规律

为分析热障涂层(TBCs)在高温盐雾腐蚀等恶劣服役环境下导热系数的变化规律,采用格子玻尔兹曼(LBM)方法,并利用涂层隔热温差分析模型系统地研究了陶瓷层(TC)厚度、黏结合金层(BC)厚度以及烟气侧和冷却空气侧对流传热系数对涂层隔热温差的影响。结果表明:涂层的隔热性能在腐蚀反应发生后迅速衰减;随着烧结的发生,涂层的有效导热系数增大,其隔热性能变差;陶瓷层厚度对涂层的隔热性能起决定性作用,涂层隔热性能随陶瓷层厚度的增加几乎线性增大,而黏结合金对涂层隔热性能的影响很小;烟气对流传热系数增大会导致叶片基体温度升高,而冷却空气对流传热系数增大则有助于降低叶片基体温度。     

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。     

Heat transfer characteristics of SA-178 boiler tubes covered with erosion resistance coatings

An experimental investigation has been conducted to determine the heat transfer characteristics of SA-178 boiler tubes coated with various erosion resistant coatings. Four tubes were tested to gather data for this investigation. The three outer surface coatings employed consisted of a 0.20 mm ceramic coating, a 0.70 mm black plasma coating, and a 0.70 mm metallic coating. The improved performance of two of the coated tubes over that of the uncoated tube indicated that the addition of material to the outer surface of these tubes did not decrease the tubes overall heat transfer coefficient. This would be expected if conduction were in fact the sole heat transfer mode experienced by the tubes. Radiation heat transfer in conjunction with the outer surface finish of the tubes were the dominant factors leading to the improved heat transfer capability of the ceramic and black plasma coated tubes.     

Heat losses from a salt-gradient solar pond

A theoretical approach for the calculation of heat losses from a cylindrical flat-bottomed salt-gradient solar pond is discussed. Steady-state heat losses from the sides and bottom of the pond have been estimated, when the pond is uninsulated as well as insulated. The insulating materials considered in the present study are dry sand, mud powder, dry cement, marble dust and mica powder. The effective insulation is varied by varying the thickness and interstitial air pressure of the insulating materials. We find that the losses are reduced to a minimum with a marble dust wall of thickness 0·20 m at an interstitial air pressure of 0·5 mm of mercury.     

Heat Transfer Processes in Low-Heat-Rejection Diesel Engines

The past five years have seen considerable interest in the possibility of constructing diesel engines in which all or part of the combustion chamber is insulated from the environment. either by ceramic materials or by high-temperature alloys backed with an air gap. It is hoped that such a design will permit engine mass to be reduced by the elimination of water cooling, and engine efficiency to be increased by the use of a secondary cycle to extract heat from the exhaust gases. In assessing the practicality of an uncooled engine, it is essential to establish the degree of insulation achievable by a proposed design. This requires identification of the principal heat loss mechanisms. This paper describes the construction of a three-dimensional time-varying combustion-chamber model, and shows that the cyclic motion of the piston leads to an important heat loss not calculable by static models. Insulation is shown to increase the importance of this loss mechanism. Estimates of the loss are given. By adapting methods established for the analysis of thermal regenerators, an approximate closed-form expression for the heat loss is obtained.     

陶瓷隔热发动机缸内传热研究

本运用１维边界层传热模型研究了燃烧室壁面温度变化引起边界层厚度及层中气体性质变化对缸内传热的影响，分析了陶瓷隔热发动机制工内的传热特性，并对其燃油消耗率上升，排温增高等原因，做出了合理的阐述。     

摩托车排气烟度及其测试方法的试验研究

通过大量的试验研究,本文对摩托车排烟特性进行了总结、归纳,并提出了一种简便易行的摩托车排烟测试方法,同时对方法的重复性、区分性进行了试验验证。用此方法对部分摩托车的排气烟度进行测试,发现一些摩托车的排烟超过30％。试验说明对摩托车排气烟度进行限制势在必行。     

柴油机缸内近气缸盖壁面边界层预测模型的研究

分析了缸内壁面速度边界层和热边界层的形成过程,建立了缸内近气缸盖壁面面湍流速度壁面函数和温度壁面函数,研究了边界层内的速度分布、温度分布及速度边界层厚度和热边界层厚度,并将预测结果与拖动发动机的实测值进行了比较,发现两的趋势是一致的。研究结果表明,缸内近气缸盖壁面有边界层形成,同一位置的速度边界层与热边界层的厚度很接近,不同位置的边界层厚度不同,大约在2mm-4mm左右。     

绝热发动机表面瞬态传热的实验研究与解析计算

以绝热发动机燃烧室陶瓷涂层表面的实测瞬态温度和平均热流为边界条件，应用傅里叶数学分析理论，探索出一种确定陶瓷涂层表面局部瞬态热流的数学方法；并结合带陶瓷涂层的２１００型低散热发动机，给出实际计算结果。     

Experimental and numerical study of the natural convection from a heated horizontal cylinder wrapped with a layer of textile material

Natural convection heat transfer enhancement from a horizontal cylinder with a textile coating is studied experimentally and numerically. The coating layer may be used for two purposes. According to the thickness of the coating it may be used as an insulating material or for surface augmentation. In the experimental study, two cylinders having different diameters of 4.8 mm and 9.45 mm are used. The bare cylinders having a radius smaller than a certain critical size were wrapped with a textile material. Wrapped cylinder diameters were increased to 9 and 12.8 mm respectively after coating and constant heat flux was applied to all bare and wrapped cylinders. Experimental study was carried out at different ambient temperatures in a conditioned room which can be maintained at a stable required value and inside a sufficiently designed test cabin. The ambient and cylinder surface temperatures (T_∞ and T_w) varied between 10 °C – 40 °C and 20 °C – 60 °C respectively. Heat transfer rates from bare and wrapped horizontal cylinders were compared and heat transfer enhancement was observed. On the basis of the experimental data average Nusselt numbers were calculated and compared with the well known correlations on natural convection heat transfer from a horizontal cylinder in the specified range of Rayleigh number, and it is seen that the results are in good agreement. The problem is also investigated numerically. Experimental and the numerical results fall in ± 30% band.     

1180℃烧结炉专用工装设计

燃气轮机零部件"火焰筒"陶瓷烘干以后需要在1180±10℃的烧结炉内进行烧结工序,火焰筒上除了两个直径35 mm的圆孔及底部的扇形孔内壁20 mm内没有陶瓷涂层外,其他位置均涂有W-200高温陶瓷涂层,没有涂层的区域为被保护区域,可以直接与工装接触,传统工装采用一个活动销、一个固定销结构,该结构可以有效固定"火焰筒",但是工件拆装不便,工装移动时工件发生摆动,难以保证不与陶瓷涂层接触。结合之前情况对工装结构和材料进行改进,通过软件三维仿真和高温试验,成功研制出一种新的工装,有效解决了不破坏陶瓷涂层,方便工件装卸,移动时稳定性好等问题。