Binomial mixing model for premixed reacting turbulent flows applied to autoignition

A turbulent mixing model based on a stochastic process using a binomially distributed random variable is presented and tested in a premixed decaying turbulent flow. Attention is focused on the joint probability density function (PDF) of reactive and inert scalar that are calculated by the PDF transport equation. The numerical work under study is applied to a field similar to autoignition in which the initial medium is composed of partially burnt gas distributed within the fresh mixture. Three dimensional direct numerical simulation has been performed in order to check the prediction capability of the model whose results showed an excellent agreement with the data from numerical experiments. The joint PDF distribution calculated by the binomial model demonstrates that binomial sampling process successfully describes the realistic features of the PDF evolution.     

双转子连续混炼机非等温混合过程的数值模拟研究

利用PRO/E软件建立了双转子连续混炼机混炼段的三维几何模型,并应用FLUENT有限元软件对高聚物熔体在SCM50双转子连续混炼机混炼段中的流动和混合过程进行了三维非等温流场分析,给出了双转子速度场和剪应力场的基本规律.计算结果表明:螺棱顶部具有较大的剪应力和速度梯度,返混螺棱区存在回流现象.所得结论可为双转子连续混炼机的数值模拟研究提供一定的方法指导,并为其工程实践提供一定的理论指导.     

涡流喷嘴反求技术研究

涡流喷嘴是涡流管的核心部件,其结构特征直接决定涡流管能量分离效果的好坏。基于逆向工程技术,以快速模具制造技术(RT)实现快速实物特征复制,获取完整的原型表面点云信息;以逆向工程(RE)技术完成喷嘴流道高精度重建;以正向再设计完成喷嘴的改进,找到优化喷嘴结构的设计方案。     

喷嘴参数对柴油机喷油规律与性能的影响

采用广安博之(Hiroyasu)等准维模型,建立高原运行柴油机工作过程模型;基于一维非定常可压缩理论建立柴油机喷射系统模型,二者耦合计算高原环境喷油器主要结构参数对柴油机实际运行时的喷油规律、燃烧特性和输出性能的影响.台架试验验证了模型的可信性.结果表明:喷孔数和喷孔直径对喷油规律影响最为敏感,喷孔夹角对喷油规律影响微弱.在海拔4 000m时,针对该型柴油机,喷孔面积存在一个最优区间,在该区间给出了功率变化率和喷孔面积的关系式.在燃烧室结构和供油系统参数不变的情况下,当喷孔面积减小为原喷孔的25%～60%时,柴油机功率最大提升8.5%;油耗最大下降8.8%,排气温度下降35℃以上.但是缸内温度明显上升,NOx排放恶化.研究为通过优化喷油器参数改善高原运行柴油机燃烧和性能提供了参考.     

Characteristics of self-excited combustion oscillation and combustion control by forced pulsating mixture supply

Characteristics of self-excited combustion oscillation are experimentally studied using confined premixed flames stabilized by a rearward-facing step. A new idea to suppress combustion oscillation was applied to the flames. The characteristics of unsteady combustion were examined, which is driven by forced pulsating mixture supply that can modulate its amplitude and frequency. The self-excited combustion oscillation having weaker flow velocity fluctuation intensity than that of the forced pulsating supply can be suppressed by the method. The effects of the forced pulsation amplitude and frequency on controlling self-excited combustion oscillations were also investigated comparing with the steady mixture supply. The unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillations, and it also exhibits desirable performances, from a practical point of view, such as high combustion load and reduced pollutant emissions of nitric oxide.     

沥青混合料强制式搅拌机拌臂布置形式的试验研究

根据搅拌机内沥青混合料的运动特点,分析了拌臂不同布置形式与混合料的相互作用关系,并在试验研究的基础上,给出了拌臂的合理布置形式.结果表明:合理的拌臂布置要在不破坏物料大循环的前提下,尽可能加快物料轴向循环的频次.推荐采用拌臂对置排列.     

氧枪喷头车削专用夹具的设计

炼钢转炉氧枪喷头喷氧孔布置在圆锥面上,且孔型特殊,加工表面质量要求高,造成加工难度较大.为解决这一加工难题,应利用车床便于加工复杂孔型且加工精度高的特点,采用设计车削专用夹具对工件加工的方法.这一专用夹具,通过对夹具体的合理结构设计,实现待加工孔中心线与车床主轴中心线对齐,较好地解决了工件准确定位问题,利用胀套结构实现...     

Improvement of flame stability and NOx reduction in hydrogen-added ultra lean premixed combustion

Lean premixed combustion is a well known method in gas turbine combustors that can reduce fuel consumption and decrease flame temperature. In lean premixed flames, flame instabilities can occur because the combustion takes place near the lean flammable limit. For the purpose of increasing flame stability, a small amount of hydrogen was added into a fuel, which has ultra low lean flammable limit. The extinction stretch rate increased and total equivalence ratio at extinction decreased with hydrogen addition; consequently, ultra lean premixed combustion was possible and flame stability could be achieved at low temperature conditions. The NO_x emission increased with hydrogen addition for the same stretch rate and equivalence ratio, but the extinction stretch rate and lean flammability limit was enlarged. Consequently, NO_x emission decreased with hydrogen addition in the near extinction conditions. Hydrogen addition could improve flame stability and reduce NO_x emission in ultra lean premixed combustion. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Dr. Eun-Seong Cho received his B.S. and M.S. degrees in Mechanical Engineering from Hanyang University, Korea, in 1996 and 1998, respectively. He then received his Ph.D. degree from Seoul National University, Korea, in 2005. He was a principal engineer of KD Navien research center and currently a research associate at Delft University of Technology, The Netherlands. His research interests include eco-friendly clean combustion technology, new and renewable energy systems. Prof. Suk Ho Chung received his B.S. degree from Seoul National University, Korea, in 1976 and Ph.D. degree in Mechanical Engineering from Northwestern University, USA, in 1983. He is a Professor since 1984 in the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests cover combustion fundamentals, pollutant formation, laser diagnostics, and plasma-assisted combustion.     

Development of a multi-optical source rapid prototyping system

Two sets of optical sources with different laser beam diameter are integrated into a rapid prototyping system for increased machining speed in this research. The smaller laser beam is used to scan the object contour to obtain an accurate machining surface and the larger laser beam is used to quickly scan the inner part of the contour without precision control limitation to save machining time. The fabrication parameters of this system are investigated based on product quality and accuracy of practical implementations. The path planning of the inner part and the outer contour are discussed. The user-friendly man-machine interface is developed using the Visual Basic program .     

用于燃烧场诊断的分子滤波瑞利散射技术

为了测量燃烧场的热力学性质,研究了分子滤波瑞利散射技术.分子滤波瑞利散射技术采用窄线宽激光器、分子滤波器和像增强CCD相机,通过分子吸收凹陷检测激光片照射流场产生散射光的频谱,抑制背景杂散光和米散射,解析流场热力学信息.建立了分子滤波瑞利散射诊断系统和分子滤波器,根据测得的滤波图像和碘蒸气吸收光谱,获得了甲烷一空气预混...     

Application of rapid prototyping and rapid tooling for development of patient-specific craniofacial implant: an investigative study

In today’s competitive world, the life-style of the average human being has become very fast. This causes a huge number traffic accidents resulting in various types of injuries. In India, most of these accidents take place during bike riding and this causes different types of fracture of bones. One of these injuries is head injury. For the proper treatment of such patients, demands for patient-specific craniofacial bio-implants are increasing day by day. This kind of ‘tailored’ implant development through near net shape manufacturing is a highly challenging task since the developmental time and cost has to be as low as possible. At the Central Mechanical Engineering Research Institute (CMERI), one such process of implant development was explored taking one case of head injury. The implant was developed through the “3D CAD-rapid prototyping (RP)-rapid tooling (RT)-investment casting (IC)” route. For achieving the task, only the facilities available at CMERI were utilized.     

基于焊接的金属成型技术的发展

快速成型技术发展至今，金属材料直接成形已成为其研究热点和一个重要发展方向。这里介绍了金属直接成型技术的工艺方法，并详细阐述了焊接快速成型工艺的发展情况及其关键技术。焊接成型技术是一种非常实用且制造成本低的快速制造方法，成型零件具有优良的强度和性能。随者焊接成型的深入研究和关键问题的解决，其必将在制造领域发挥巨大作用。     

An experimental study on combustion processes and nox emission characteristics of the air-staged burner

The combustion processes and emission characteristics in air-staged burner have been experimentally studied. The light fuel oil doped with pyridine(C₅H₅N) is used to investigate the fuel NO_X emission characteristics. Experiments are carried out for a wide range of operating conditions of single-staged and multi-staged burner. The detailed discussions are made for the flame structure of the air-staged burner as well as effects of excess air ratios, staged air flow percentage, and spray conditions on flame pattern and NO_X emission characteristics.     

A study on the usability of biodiesel fuel derived from rice bran oil as an alternative fuel for IDI diesel engine

The world is faced with a problem of air pollution due to the exhaust emissions from automobile. Recently, lots of researchers have been attracted to develope various alternative fuels and to use renewable fuels as a solution of these problems. There are many alternative fuels studied in place of diesel fuel made from petroleum. Biodiesel fuel (BDF) is a domestically produced, renewable fuel that can be manufactured from vegetable oils, used vegetable oils, or animal fats. In this study, the usability of BDF, one of the oxygenated fuels as an alternative fuel for diesel engines was investigated in an IDI diesel engine. Emissions were characterized with a neat BDF and with a blend of BDF and conventional diesel fuel. Since the BDF includes oxygen of about 11%, it could influence the combustion process strongly. Therefore, the use of BDF resulted in lower emissions of carbon monoxide and smoke emissions with some increase in emissions of oxides of nitrogen. It is concluded that BDF can be utilized effectively as a renewable fuel for IDI diesel engines.     

A study on the rapid bulk combustion of premixture using the radical seeding

The objective of this study is the rapid bulk combustion of mixture in a constant volume chamber with a tiny sub-chamber. Some narrow passage holes were arranged to induce simultaneous multi-point ignition in the main chamber by jet of burned and unburned gases including radicals from the sub-chamber, and the equivalence ratios of pre-mixture in the main chamber and the sub-chamber were the same. The principal factors of the Radical Induced Auto-Ignition (RIAl) method are the diameter of the passage holes and the volume of sub-chamber. The relationship between the sub-chamber and diameter of passage hole was represented by the ratios of sub-chamber volume to passage hole volume. The ratios are non-dimensional coefficients for sub-chamber characteristics. As a result, the RIAI method reduced the combustion period, which expanded the lean limit in comparison with SI method.     

基于C群的燃油箱设计软件开发

利用c拌作为开发语言,以VisualStudio2008作为开发工具,开发了燃油箱设计软件。为提高设计效率,使用Access数据库技术储存标准零部件参数,并在设计过程中根据设计要求筛选数据以帮助用户选择。同时采用ActiveXAutomation技术对AutoCAD和SolidWorks进行二次开发,生成设计图纸。     

Investigation of complex rapid EDM electrodes for rapid tooling applications

This paper describes a collaborative research programme aimed at investigating the use of quick EDM electrodes obtained via appropriate rapid prototyping techniques in finishing laser-sintered tools. Two methods were employed in obtaining the EDM electrodes: copper coating of stereolithography models and copper coating of direct metal laser sintered (bronze) models.The amount of copper deposited on both electrode models proved problematic as the electroplating process was unable to deposit enough copper in the inner cavities of the electrodes, with very gradual reduction in copper layer thickness from the outer faces/surface to virtually no deposition in the inner walls and bottom face. Consequently, the electrodes were not suitable for the envisaged EDM process.     

大功率柴油机燃烧室优化及其与喷油嘴的匹配试验

运用仿真与试验相结合的方法,利用KIVA-3软件对燃烧室进行了优化研究,确定燃烧室的优选方案。并在一台模拟增压单缸机上对燃烧室的优选方案与不同方案喷油嘴进行优化匹配试验,确定喷油嘴最佳方案。结果表明:采用燃烧室B和8×Ф0.42 mm喷油嘴,可以达到研究目的。     

Simulation of the fluidic features for diffuser/nozzle involved in a PZT-based valveless micropump

PZT-based valveless micropump is a microactuator that can be used for controlling and delivering tiny amounts of fluids, and diffuser/nozzle plays an important role when this type of micropump drives the fluid flowing along a specific direction. In this paper, a numerical model of micropump has been proposed, and the fluidic properties of diffuser/nozzle have been simulated with ANSYS. With the method of finite-element analysis, the increased pressure drop between inlet and outlet of diffuser/nozzle induces the increment of flow rate in both diffuser and nozzle simultaneously, but the increasing rate of diffuser is faster than that of nozzle. The L/R, ratio of L（length of cone pipe） and R （radius of minimal cross section of cone pipe） plays an important role in fluidic performance of diffuser and nozzle as well, and the mean flow rate will decrease with increment of L/R. The mean flow rate reaches its peak value when L/R with the value of 10 regardless the divergence angle of diffuser or nozzle. The simulation results in-dicate that the fluidic properties of diffuser/nozzle can be defined by its geometric structure, and accordingly determine the efficiency of micropump.     

Prism Signal Processing of Coriolis meter data for gasoline fuel injection monitoring

Prism Signal Processing is a new recursive FIR technique offering rapid filter design and calculation. It has previously been applied to Coriolis mass flow metering to generate fast (48 kHz) flow measurement updates, facilitating for the first time the direct mass flow measurement of individual fuel pulses injected into a laboratory diesel fuel injection test bench. In this paper we describe an augmented sensor signal filtering scheme which enables rapid tracking of the desired mode of flow tube vibration while notching out undesired modes. The new scheme is applied to a gasoline injection test bench where the vibrational interference is greater than for the previously described diesel system due to increased hydraulic shock. The paper presents experimental findings which illustrate the further challenges to be overcome in order to achieve the goal of traceable direct mass flow measurement of individual fuel injection pulses. For example, when a fuel pulse is shorter than the resonant period of the flow tube, the observed phase difference appears to show dependence on the instantaneous phase of the flow tube vibration.