氢气／空气当量比对微燃烧器燃烧特性的影响

以美国麻省理工学院(MIT)研制的硅基六晶片微燃烧器为研究对象,采用考虑了基元反应动力学机理燃烧程序的二维计算流体动力学(CFD)数值分析方法,研究了在微尺度燃烧器入口处混合气体流量不变的情况下,改变氢气/空气当量比对微尺度燃烧器燃烧特性的影响.整个模拟计算主要包括混合气体的流动路径、微燃烧器的内部区域以及整个燃烧器的墙壁面;计算过程中考虑了氢气/宅气的流体动力学特性、传热学特性和详细的基元反应机理.计算结果显示,当氢气/空气当量比为0.4时,燃烧器发生熄火;当量比为0.5、0.6时,燃烧器内部能维持稳定燃烧;当量比为0.7时,燃烧器的微细通道内出现同燃现象.结果表明,利用二维CFD数值模拟的方法研究微尺度燃烧器燃烧特性足可行的.     

微空间下氢氧催化燃烧特性的数值分析

以CHEMKIN-IV中高速柱塞流反应器(PFR)作为燃烧室模型进行仿真分析.基于氢氧十九步基元反应化学动力学机理,分析了反应压力、当量比、进气流速对微空间下氢氧燃烧的影响.获得了燃烧室轴向温度场随当量比系数的变化规律,发现其最高温度出现在当量比约为1时,分析了较高的反应压力有利于提高微燃烧器氢氧燃烧效率,但过高的反应压力将导致微小空间燃烧着火滞后时间增加,使Damk(O)hler数降低.这些特性分析为Power MEMS的设计提供科学依据.     

基于CFD的钻头喷嘴水力特性分析

喷射钻井的实践和理论研究表明,喷射钻头不仅靠牙轮进行机械破岩,钻头喷嘴还是一个水力机械,高速射流的水力能量不仅能净化井底的岩屑,还具有直接破碎岩石的冲蚀作用.文中以基础流体力学理论和流场模拟来分析喷嘴的水力性能,建立不同结构喷嘴的CFD模型,对比分析各型喷嘴的水力性能,为牙轮钻头上喷嘴的选用与设计提供了理论依据.     

涡流强度对增压柴油机燃烧和排放特性影响的仿真研究

文章首先建立了16V132增压柴油机的燃烧系统仿真模型,之后进行了不同涡流强度方案下的整机燃烧过程CFD仿真计算,分析了涡流强度对发动机发电工况下的燃烧特性和排放特性影响规律,最终确定了合适的燃烧过程涡流比,为16V132增压柴油机燃烧系统的匹配设计提供理论指导。     

反应压力对微小空间氢氧燃烧过程影响的数值分析

基于氢氧19步基元反应化学动力学机理,对微燃烧器氢氧燃烧过程进行数值分析.研究表明:受反应机理控制,反应压力对微小空间燃烧过程的影响呈现复杂的非线性特性;较高的反应压力有利于提高微燃烧器氢氧燃烧效率,减少表面传热损失对微小空间燃烧稳定性和充分性的不利影响;但高压下链终止基元反应的主导作用导致微小空间燃烧着火滞后时间增加,使DamkOhler数降低,从而不可能无限制地提高反应压力来强化微燃烧器的燃烧负荷率.     

基于CFD的磁流体轴承润滑膜特性分析

磁流体轴承具有转速高、密封性好、承载力强等优点,符合高速铁路中的应用需求。提出一种磁流体轴承结构,并运用CFD方法对轴承润滑区的承载性能以及热效应问题进行了仿真计算,在此基础上进一步分析了偏心率对轴承承载力及温升的影响规律,为之后磁流体轴承的进一步设计提供帮助。     

基于CFD技术的电动截止阀流场特性研究

根据电动截止阀的结构尺寸建立其流道模型,采用计算流体动力学(C FD)方法对截止阀的内流道进行动态数值计算,在截止阀开启80％ 和100％ 两种状态下,得到流道内流体的速度和压力分布情况.通过C FD技术对截止阀内流体流动状况进行模拟,能够确定流体通过阀道时压力、速度的变化和产生涡流、回流的位置,为截止阀工作性能改善、...     

基于CFD技术的节流阀流量特性的数值模拟分析

采用计算流体动力学(简称CFD)方法对节流阀内部结构流量特性进行了数值模拟和分析,利用Solid Works Flow Sim ulation模块进行仿真,用数值模拟的方法得出其流量特性Kv值,从而为节流阀结构的设计提供相应理论依据。     

微尺度下氢氧预混合气催化燃烧的研究

基于空间气相和表面催化的详细化学反应机理,应用计算流体动力学软件对亚毫米燃烧器内的氧氧预混合燃烧进行模拟,在对催化燃烧模型进行试验验证的基础上,讨论不同反应模型的燃烧特性以及壁面材料和进口流速等对催化燃烧反应的影响.模拟结果显示,表面催化反应会使壁面相邻位置空间气体内的OH质量分数降低,对该催化壁面临近区域的气相反应有所抑制;壁面催化反应与空间气相反应耦合进行时,燃烧效率可达到最大值;进口速度对出口排气温度的影响要大于对外壁面最高温度的影响,进口速度过高会导致燃烧效率降低;燃烧器材料的选择也对催化燃烧有着重要的影响,采用热导率较小的材料时,燃烧器壁面存在较高的温度梯度,燃烧器外壁面温度也较高,而采用热导率较大的材料时,壁面对进口端的气体预热作用增强,高温燃烧区域向入口端移动.     

燃烧室结构对天然气转子发动机燃烧过程的影响

以一台由端面进气汽油转子发动机改装而来的预混天然气转子发动机为研究对象,在FLUENT软件的基础上通过编程实现转子发动机三维网格的偏心运动,并选择合适的湍流模型、燃烧模型以及详细的CHEMKIN化学反应机理,建立基于化学反应动力学的端面进气天然气转子发动机三维动态数值模拟模型。通过与试验数据进行对比和分析,验证模型的可靠性。在此基础上,研究燃烧室结构对端面进气天然气转子发动机的缸内流场、温度场和中间产物浓度场的影响。结果表明,当燃烧室凹坑布置于转子曲面长度方向的前端和转子曲面宽度方向的中心时,燃烧过程同时利用了燃烧室后部的滚流以及燃烧室中部高速流区对火焰的加速作用,缸内整体燃烧速率最大。同时,其缸内压力最大以及中间产物OH的生成量也最大,其压力峰值比中置凹坑燃烧室提高了19.9%,但其NO质量分数仍在0.5%以内。     

Ignition and combustion characteristics of the gas turbine slinger combustor

This paper describes the ignition and combustion characteristics of a gas turbine slinger combustor with rotating fuel injection system. An ignition test was performed under various airflow, temperature and pressure conditions with fuel nozzle rotational speed. From the test, there are two major factors influencing the ignition limits: the rotational speed of the fuel nozzle, and the mass flow parameter. Better ignition capability could be attained through increasing the rotational speed and air mass flow. From the spray visualization and drop size measurement, it was verified that there is a strong correlation between ignition performance and drop size distribution. Also, we performed a combustion test to determine the effects of rotational speed by measuring gas temperature and emission. The combustion efficiency was smoothly enhanced from 99% to 99.6% with increasing rotational speed. The measured pattern factor was 15% and profile factor was 3%.     

Vibration assisted electrochemical micromachining of high aspect ratio micro features

The most used processes for generation of high aspect ratio microchannels are Nd: YAG laser technology on silica substrate and ultra violate lithography (UV-LIGA) process on metals. There are a few micromachining technologies such as micro mechanical milling, micro electro discharge machining (EDM) and electrochemical micromachining (EMM) for production of high-aspect-ratio micro features on highly stressed and anticorrosive metal like stainless steel. This paper discusses the micro fabrication of high aspect ratio micro features at the intended location on high strength stainless steel sheet of very small thickness to high thickness with highest average aspect ratio 14.33 achieved during microchannel generation by EMM with the help of coated microtool. Mathematical model relating aspect ratio with various parameters and machining conditions is derived to explore the ways to increase the aspect ratio of micro features. Experimental investigations were carried out to know the effect of vibration of microtool, frequency of pulsed voltage, microtool tip shape, thickness of work piece and non-conducting layer coated microtool on high aspect ratio micro features. Vibration of microtool with very small amplitude improved the stability of micromachining due to improved flow of electrolyte.     

Analysis of the combustion instability of a model gas turbine combustor by the transfer matrix method

Combustion instability is a major issue in design of gas turbine combustors for efficient operation with low emissions. A transfer matrix-based approach is developed in this work for the stability analysis of gas turbine combustors. By viewing the combustor cavity as a one-dimensional acoustic system with a side branch, the heat source located inside the cavity can be described as the input to the system. The combustion process is modeled as a closed-loop feedback system, which enables utilization of well-established classic control theories for the stability analysis. Due to the inherent advantage of the transfer matrix method and control system representation, modeling and analysis of the system becomes a straightforward task even for a combustor of the complex geometry. The approach is applied to the stability analysis of a simple combustion system to demonstrate its validity and effectiveness. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Dong Jin Cha received his B.S. and M.S. degrees from Hanyang University in Seoul, Korea, in 1981 and 1983, respectively. He then received his Ph.D. in ME from the University of Illinois at Chicago in 1992, and worked at the US DOE NETL for the next three years as a National Research Council (NRC) Associate. Dr. Cha is currently a Professor at the Department of Building Services Engineering at Hanbat National University in Daejeon, Korea. His research interests include combustion instability of gas turbine for power generation and fluid flows in building services engineering. Jay H. Kim received his BSME from Seoul National University in 1977, MSME from KAIST in 1979 and Ph.D. in ME from Purdue University in 1988. He has joined the Mechanical Engineering faculty of the University of Cincinnati in 1990, and is currently a Professor. Before joining the University of Cincinnati, he worked in industry for six years in Korea and US. His research interests have been in broad areas of acoustics, vibrations and applied mechanics with recent focuses on human/bioacoustics and vibration, gas pulsations and elastic stability. Yong-Jin Joo received his BSME and MSME from Sung Kyun Kwan University in Seoul, Korea, in 1990 and 1992, respectively. Mr. Joo is currently a Project Leader for IGCC Operation Technologies at KEPRI (Korea Electric Power Research Institute) which is the central R&D center of KEPCO (Korea Electric Power Corporation). His research interests include the development of operation and maintenance simulator for power plants including IGCC.     

某重型燃气轮机燃烧室燃烧流动的数值模拟

对某重型燃气轮机燃烧室燃烧天然气进行数值模拟,在模拟过程中采用了雷诺应力模型、EBU-Arrheniue湍流燃烧模型和六通量辐射模型来描述其燃烧流动过程,运用FLUENT软件求解了三维流场和温场分布.计算结果能够很好地反映该重型燃气轮机燃烧室燃烧流动特点,对预测燃烧室内的燃烧流动有一定参考价值.     

Spray and combustion characteristics of a dump-type ramjet combustor

Spray and combustion characteristics of a dump-type ram-combustor equipped with a V-gutter flame holder were experimentally investigated. Spray penetrations with a change in airstream velocity, air stream temperature, and dynamic pressure ratio were measured to clarify the spray characteristics of a liquid jet injected into the subsonic vitiated airstream, which maintains a highly uniform velocity and temperature. An empirical equation was modified from Inamura’s equation to compensate for experimental conditions. In the case of insufficient penetration, the flame in the ram-combustor was unstable, and vice versus in the case of sufficient penetration. When the flame holder was not equipped, the temperature at the center of the ram-combustor had a tendency to decrease due to the low penetration and insufficient mixing. Therefore, the temperature distribution was slanted to the low wall of the ramcombustor. These trends gradually disappeared as the length of the combustor became longer and the flame holder was equipped. Combustion efficiency increased when the length of the combustor was long and the flame holder was equipped. Especially, the effect of the flame holder was more dominant than that of the combustor length in light of combustion efficiency.     

微细立铣削切削振动试验研究

基于45钢微细立铣削试验,分析了微细立铣削切削振动的基本特征,研究了直槽立铣加工时铣削参数对振动加速度和振动位移量影响的基本规律.研究结果表明:在同样的切削工况下,微细立铣削的切削振动远大于大直径立铣刀铣削的情况;铣削参数是振动加速度的主要影响因素,振动加速度随铣削参数的增加都呈上升趋势,但轴向切深H和转速n对振动加速度的影响比进给量f更显著;在一定的参数范围内,减小主轴转速n和增大轴向切深H能够减小振动位移量的大小.     

Effect of cation on micro/nano-tribological properties of ultra-thin ionic liquid films

Room temperature ionic liquids (RTILs) have some unique characteristics which meet the requirements as high performance lubricants. In this work, three kinds of RTILs films with the same anion but different cations were prepared on single-crystal silicon wafer by dip-coating method. Thermal stability of the RTILs was evaluated using thermal gravity analysis in a nitrogen atmosphere. The morphology, nano-friction and nano-adhesion properties of the RTILs films were experimentally investigated at nano-scale using AFM/FFM. Chemical compositions of the films were characterized with a multi-functional X-ray photoelectron spectrometer. Micro-tribological properties of RTILs films were investigated using AISI-52100 steel ball in ball-on-plate configuration, and compared with perfluoropolyether. The worn surface morphologies were measured with a 3D optical surface profilometer. Results show that 3-butyl-1-methyl-imidazolium tetrafluoroborate exhibited the best anti-wear ability in comparison with the other three lubricants. RTILs films could be used as a kind of novel lubricant for application in M/NEMS. The corresponding friction-reduction and anti-wear mechanisms of the tested ultra-thin RTILs films under tested condition were proposed based on the experimental observation. The investigation revealed that friction-reduction and anti-wear properties of RTILs were strongly dependent on their chemical structures. For the friction at nano-scale, the flexibility and surface energy of the lubricant played significant role, while for the friction at micro-scale, both the rigid cycle structure and flexible chain of the RTILs played crucial role.     

Investigations on the effect of measurement errors on estimated combustion and performance parameters in HCCI combustion engine

Several parameters derived from heat release analysis are used for combustion diagnostics and control in internal combustion engines. It is important to tune the input parameters used in heat release calculations, in order to get correct estimation of heat release rate. In this study, tuning of input parameters is carried out by using cumulative heat release calculations of cylinder pressure during motoring. This tuning procedure uses offline iterative processing of motoring in-cylinder pressure data. The tuned parameters obtained from this method can also be utilized for online analysis of combustion parameters. Input parameters used in these investigations are intake air temperature, intake air pressure, phasing between the acquired pressure and crank angle position, compression ratio and scaling factor of heat transfer coefficient. Effect of error in these input parameters on estimated combustion and performance parameters like IMEP, combustion phasing, combustion duration, heat release rate, and maximum mean gas temperature are evaluated. The relative importance of measurement error in input parameters and its maximum expected error in the final results is analyzed in a HCCI combustion engine. Results shows that measurement errors in phasing between pressure and crank angle position, compression ratio and inlet air pressure affect estimated combustion and performance parameters significantly.     

A modeling study of local equivalence ratio fluctuation in imperfectly premixed turbulent flames

The effect of fluctuation of Equivalence Ratio (ER) in a turbulent reactive field has been studied in order to check the global combustion characteristics induced by the local fluctuation. When the flow is premixed on a large scale, closer examination on a small scale reveals that local fluctuations of ER exist in an imperfectly premixed mixture, and that these fluctuations must be considered to correctly estimate the mean reaction rate. The fluctuation effect is analyzed with DNS by considering the joint PDF of reactive scalar and ER, followed by modeling study where an extension of stochastic mixing models accounting for the ER fluctuation is reviewed and tested. It was found that models prediction capability as well as its potential is in favor to this case accounting the local ER fluctuation. However, the effect of local fluctuation did not show any notable changes on the mean global characteristics of combustion when statistical independence between the reactive scalar and ER field is imposed, though it greatly influenced the joint PDF distribution. The importance of taking into account the statistical dependency between ER and combustible at the initial phase is demonstrated by testing the modeled reaction rate.