车用柴油机微粒捕捉器的系统模拟

提出了一个车用柴油机微粒捕捉器（DPF）的系统模拟数学模型。利用数学模型可以对DPF在汽车实际运行过程中的性能,包括DPF再生的时间间隔,排气阻力特性以及DPF的使用对汽车附加能量的消耗等随汽车实际运行工况的变化进行分析研究,为汽车DPF的优化设计提供参考数据,并可以对DPF实际使用中的一些性能进行预测。     

GDI发动机燃用甲醇及甲醇/汽油混合燃料的微粒排放特性研究

在缸内直喷汽油机上进行了燃用纯甲醇和甲醇/汽油混合燃料的微粒排放特性研究,分析了点火定时、喷油定时和过量空气系数对微粒排放的影响规律。试验结果表明:在选定的发动机典型常用运行工况下,燃用纯甲醇燃料(M100)时,缸内直喷汽油机几乎不产生微粒排放;燃用甲醇/汽油混合燃料时(M20或M25),排气微粒数浓度主要集中在核态微粒区域,微粒质量浓度主要集中在积聚态微粒区域,其中M25燃料的微粒排放性要优于M20燃料;随着点火定时的提前,排气微粒数浓度和质量浓度均有所升高;随着喷油定时的提前,排气微粒数浓度降低,微粒质量浓度升高。     

湍流管流中柴油机微粒沉降特性的模拟研究

应用 CFD 软件对湍流管流中柴油机微粒的沉降特性及其影响因素进行了研究.分析了对柴油机微粒沉降具有重要影响的湍流管流中流场的结构特征,研究了微粒热泳沉降和湍流脉动沉降特性以及两者在微粒沉降中的相互作用,并对影响微粒沉降的各种因素进行了分析.通过研究,获得了湍流管流中柴油机微粒的沉降特性和沉降规律,研究结果可以为柴油机微粒沉降的控制以及微粒热泳净化技术的研究提供一定的依据.     

柴油机排气微粒旋流净化技术的初步研究

根据柴油机排气微粒净化的要求,研制了一台柴油机排气微粒轴流直流式旋流净化器,并对旋流净化器的净化特性进行了初步的理论分析和试验研究,研究结果表明,排气微粒旋流净化技术对净化柴油机排气微粒是有效的;柴油机运行工况及旋流子结构参数对排气微粒净化效率有一定影响;排气微粒的凝聚是微粒旋流分离净化的前提。通过对净化器结构的优化以及采取必要的微粒凝聚措施,相信会显地提高柴油机排气微粒旋流净化器的净化效率,利     

层流管流中不同入口类型下柴油机微粒的热泳沉降

采用临界轨道半径思想,对层流管流中不同入口类型下柴油机微粒的热泳沉降特性进行了研究.给出了3种不同入口类型条件下层流管流入口段流场以及微粒热泳沉降的求解方法;分析了对柴油机微粒热泳沉降具有重要影响的层流管流流场的结构特征;在此基础上,对不同入口类型层流管流入口段中柴油机微粒的热泳沉降特性及其影响因素进行了分析.通过研究,获得了柴油机微粒在不同入口类型层流管流入口段中的热泳沉降规律.     

湍流通道内微粒受力对其输运特性的影响

柴油机排气过程中的微粒运动和沉降对微粒测量、排气再循环系统的正常工作以及微粒的净化捕集等具有重要的影响.利用微粒受力模型和微粒随机轨道模型,对湍流通道中微粒的输运特性以及微粒受力对其输运特性的影响进行了分析.通过研究,给出了重力、热泳力和Saffman升力在不同条件下对湍流通道内微粒输运特性的影响规律.研究结果对于加深柴油机微粒在湍流通道中运动及沉降规律的理解具有重要的意义.     

汽车排气微粒演变特性的参数分析

通过理论分析的方法对汽车排气尾流中的微粒演变特性进行了研究．建立了描述汽车排气尾流中微粒演变过程的核化模型和凝并模型．在此基础上,对排气微粒在尾流中的核化与凝并过程以及影响因素进行了分析．研究结果表明：核化增加了尾流中超细微粒的数量;燃料硫含量、排气稀释比、尾流温度以及相对湿度等对微粒的核化有较大的影响;凝并将显著改变尾流中的微粒粒径分布;排气微粒的初始数密度和粒径分布对尾流中的微粒凝并具有较大的影响．     

动态粗粉分离器结构优化与数值模拟

为提高机组运行的稳定性和经济性,将静态粗粉分离器改造成动态粗粉分离器,采用Fluent软件模拟动态粗粉分离器内部气体流场变化和颗粒运动轨迹,研究分析调节动叶轮转速、静叶转角、入口风速对动态粗粉分离器的出粉细度,分离效率,循环倍率,系统阻力等分离特性的影响变化。结果表明:在入口风速17 m/s~19 m/s,动叶轮转速70 r/min,静叶角度45°时,动态粗粉分离器各项运行指标均较理想,动态粗粉分离器处于最佳运行状态,模拟结果能为实际工程应提供了一定理论依据。在现场试验中,动态粗粉分离器各项运行特性也均优于静态粗粉分离器。     

柴油机DPF湍流通道内微粒形态对微粒输运特性的影响

利用建立的椭球形微粒的运动学方程和动力学方程以及湍流场中椭球形微粒的受力及力矩模型,对柴油机微粒捕集器(DPF)湍流通道中微粒的输运特性进行了研究,着重对微粒形态的变化对湍流通道中微粒的运动轨迹、运动方位以及沉降速度的影响进行了分析.结果表明:微粒在壁面附近存在富集现象,且这种现象随着微粒长短半轴比的增加愈发明显;随着气流速度的增加,微粒有向通道内扩散的趋势,且微粒形态对微粒运动轨迹的影响变得显著;在湍流场通道中,椭球形微粒的长轴倾向于与流体流动方向平行,微粒长轴在垂直于壁面方向和展向上的姿态角分布则比较均匀,距壁面量纲为1距离对微粒长轴取向的影响不大;微粒量纲为1沉降速度与微粒形态关系紧密,且随短半轴长的增长并非呈单调变化规律.     

柴油机排气微粒捕捉器燃气再生技术的研究

提出了一种新的柴油机排气微粒捕捉器的加热再生技术 ,即利用燃气与排气中的氧气燃烧清除微粒捕捉器中沉积的微粒 ;根据液化石油气的物化特性和排气中的含氧量 ,对这种方法的可行性进行了理论分析和试验验证 ;研制了一种以液化石油气为再生燃料的柴油机排气微粒捕捉器 ,并对燃气流量、过滤体内的微粒沉积量以及再生时间等影响因素进行了台架试验研究。     

The Effective Pore Radius of Screen Wicks

The effective pore radius in screen-wick heat pipes was investigated, which is very important for the prediction of maximum heat transfer rates due to capillary limitation. An equation for the effective pore radius of the screen wicks was derived based on the model of the screen geometry. The capillary height for stainless steel and phosphor bronze screens was measured using water, ethyl alcohol, and Freon 113 as the test liquids. The effect of surface treatment (acid cleaning and oxidation) on the capillary height was also examined. From the comparison of the experimental data for water and ethyl alcohol with those for Freon 113, it was indicated that the contact angle was 24.2° for water and 16.9° for ethyl alcohol. Consequently, it was found that the effective pore radius of the screen wicks could be predicted fairly well from the expression presented in this study, and that the contact angle should be taken into consideration to evaluate the maximum capillary pressure accurately.     

In-situ measurement and numerical simulation of nitriding kinetics of grain-oriented silicon steel

Although nitriding plays a critical role on the low-temperature production process of grain-oriented silicon steel, the quantitative modeling on nitriding kinetics is still in lack. We have in-situ measured the nitriding kinetics of grain-oriented silicon steel at 750 °C in the gas mixture of N₂ + H₂ + NH₃ using thermogravimeter (TG), and found that the kinetics could be divided into three stages. First, the weight of sample decreased until the nitriding period of 40s, indicating that no nitriding could occur but just the oxide layer on the surface be reduced. Next, the weight increased with the increasing rate until 120s, suggesting an accelerated nitriding during this period. Finally, the weight increased with a constant rate during nitriding, i.e. the nitriding with a constant rate. It was found that nitrogen atoms could diffuse into the steel matrix along the grain boundaries with the largest depth of about 50 μm during the nitriding for 590s. Moreover, the lamellar oxide particles on the surface that were formed during decarburization process transformed to the spherical ones when they were reduced by H₂ during nitriding, leading to the formation of spongy oxide layer. With a reasonable assumption that the reduction kinetics of oxide layer should determine its resistance to nitriding, we have established a mathematic modeling with a properly defined boundary condition. The calculated average N content and the N-penetrating maximum depth during nitriding both show excellent agreements with the experimental measurements.     

单晶硅片制绒后产生白斑的原因分析及改善措施

针对单晶硅片在制绒后出现的白斑及脏污现象,通过对异常硅片进行绒面测试、厚度测试和产线对比实验,排查异常现象产生的原因,并结合显微红外测试和X射线能谱分析(EDS)测试对产生异常的原因进行深入分析。分析结果表明:硅片制绒后出现白斑现象主要是硅片生产环节造成的。进刀面出现异常,一方面是由于硅片清洗液残留所致,另一方面是由于粘棒胶通过金刚线带入硅片表面后,后道工序难以清洗造成的。M2异常硅片进刀面有大片灰白状是有机硅类物质附着、粘胶导致的;M2和157.4 mm异常硅片其他异常区域有小片亮白、灰白状,主要是清洗剂中的磷酸盐、硅酸盐残留。     

Effect of thickness and surface treatment on silicon water reflectance

In this paper we present reflectance measurements on silicon wafers and the dependence of the reflectance on the thickness, on the texturization and on the back metallization. Silver and aluminum have been deposited using screen printing and also vacuum evaporation as a reference. The work was intended as a contribution to the problem of light trapping that becomes important for thin wafers for commercial, low cost, silicon cells. For the case of wafers with polished surfaces, the results are analysed to yield the reflectivity of the back surface and the total energy absorbed in the sample. Texturization, on the contrary, introduces diffraction phenomena making the evaluation of the absorbed energy more complex.     

退火硅钢高温力学性能分析

利用Gleeble-3500热模拟试验机对退火取向硅钢和无取向硅钢进行高温拉伸试验,测试硅钢在高真空度下的真应力-真应变曲线。结果表明：随着退火温度的升高,硅钢试样的屈服强度和抗拉强度呈现先增大后减小趋势;取向硅钢在900℃的高温退火后的塑性最好;拉伸温度在750℃以上时,抗拉强度都大大降低;断面收缩率随着温度的升高先增加后明显下降。     

氨水雾化电晕放电净化船舶柴油机烟气的试验设计

本文首先概述了雾化电晕放电净化烟气中颗粒物的基本原理,在此基础上提出了一种加氨雾化电晕放电法净化船舶柴油机烟气的试验设计。这种烟气净化方法在以往雾化电晕放电净化炭粒的基础上,使烟气中的NOx和SO2在一定条件下与氨反应生成铵盐颗粒,从而达到净化它们的目的。最后设计试验不同的反应温度和氨水浓度分别对NOx、SO2净化效率的影响。     

Fracture prediction of electromagnetic silicon steel in reheating furnace

This article proposes the use of strain energy density (SED) for the prediction of fracturing in silicon steel slabs undergoing reheating in a furnace. Reheating is commonly used to soften steel before hot rolling into ultra-thin silicon steel sheets referred to as electromagnetic steel. High heating rates are required to reduce the time spent in the reheating furnace to increase the efficiency of producing ultra-thin electromagnetic steel sheets and decrease fuel consumption. However, an excessive increase in heating rates may induce fracturing due to the comparatively brittle nature of the silicon used in electromagnetic steel slabs to enhance the electromagnetic properties. In this study, the authors used finite element numerical calculation to elucidate the fracture mechanism of electromagnetic steel slabs undergoing heating. The authors then used SED as a criterion by which to optimize the heating rates without inducing fracturing in electromagnetic steel. The proposed model could be used as a guide to shorten the time required for heating various types of steel in reheating furnaces.     

Wood chips size distribution in relation to blade wear and screen use

The study investigated the effect of wearing chipper knives on machine productivity, fuel consumption and particles size distribution. The test included two different tree species (poplar and pine), two tree parts (branches and logs) and two screen types (large and medium). Chip quality was defined by CEN international technical standards. Knife wear causes a significant reduction of chipping productivity and a remarkable increase of fuel consumption. The replacement of the standard wide mesh screen with a narrower screen has a similar effect, further decreasing productivity and increasing fuel consumption. For the same screen type and knife wear level, productivity and fuel consumption are the same for poplar and pine. Knife, tree species and tree part also have a significant impact on chip size distribution. Chips produced from logs always contain a smaller proportion of oversize particles and a higher proportion of accepts. For the same large mesh screen, poplar chips tend to be larger than pine chips and to contain a higher proportion of oversize particles. On the contrary, pine chips tend to be smaller and to contain a higher proportion of fines. The use of a narrower mesh screen on pine material does not seem to offer any significant reduction of oversize particles, whose presence is already very limited. Therefore, a standard large mesh screen should be used when chipping pine material.     

Active screen plasma nitriding of 316 stainless steel for the application of bipolar plates in proton exchange membrane fuel cells

Proton exchange membrane fuel cell (PEMFC) has attracted considerable interest because of its superb performance, and many researches are focused on the development of high-performance, long-life bipolar plates. Stainless steel bipolar plates offer many advantages over the conventional graphite bipolar plates, such as low material and fabrication cost, excellent mechanical behaviour and ease of mass production. However, the insufficient corrosion resistance and relatively high interfacial contact resistance (ICR) become the major obstacles to the widespread use of stainless steel bipolar plates. In this work, active screen plasma nitriding (ASPN), a novel plasma nitriding technique, was used to modify the surface of 316 austenitic stainless steel. A variety of analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), glow discharge optical emission spectrometer (GDOES), were employed to characterize the nitrided samples. The results reveal that a nitrogen supersaturated S-phase layer has been successfully produced on the surface of all nitrided 316 stainless steel samples. The interfacial contact resistance (ICR) value can be decreased dramatically after ASPN treatment and the corrosion resistance can also been improved. In addition, better corrosion resistance can be achieved by active screen plasma nitriding with a stainless steel screen than with a carbon steel screen. This technique could be used to improve the performance and lifespan of bipolar plates for fuel cells.     

28MnCr5齿轮钢中关键元素的控制研究

针对莱钢生产的28MnCr5齿轮钢中的C、Si、S、P等元素的控制工艺进行了研究,结果表明为了得到理想的成分控制,在电弧炉出钢时,应控制钢水中w(C)小于0.20％,w(P)小于0.010％,尽量减少钢水中硫含量.为防止精炼钢水增硅、回磷,电弧炉出钢严禁下渣.在VD工位,钢水中会有0.02％左右的碳增量,0.02％左右的硅增量,因此在LF调整合金成分时,应该留出一定的增量.