基于稳态流通特性的螺旋进气道结构参数灵敏度分析

为了探究设计参数对气道流通特性的影响,以GD190型单缸直喷式柴油机进气道为例,进行5因素21水平的最优拉丁超立方试验。利用AVL-Fire软件完成气道稳流试验三维数值模拟计算,采用最小二乘法建立进气道响应面模型,开展基于响应面法的面向螺旋进气道流通特性的灵敏度分析。研究结果表明:影响平均流量系数和平均涡流比最敏感的因素分别是气门喉口直径和螺旋角,要提高气道性能,不仅要考虑单个因素的影响,还要综合考虑多个因素的交互作用。灵敏度分析可为简化气道优化设计提供可靠的依据。     

基于NSGA-Ⅱ的螺旋进气道流通特性多目标优化

分析柴油机螺旋进气道结构参数对螺旋进气道流通特性的灵敏度,并以此为依据选取优化变量。以平均流量系数和平均涡流比的最大化为优化目标,基于构建的K riging近似模型,利用非支配排序遗传算法(N-dom inated Sorting G enetic A lgorithm,N SG A-II)对影响螺旋进气道流通特性的结构参数寻优求解。结果表明:相比于原始方案,优化方案的平均流量系数增加6.32%,平均涡流比增加11.03%,流通特性得到较大提升,研究内容表明所提方法的有效性。     

发动机进气道CFD分析方法

车用发动机燃烧系统开发的实际设计过程中,进气道的设计通过对缸内气体流动的影响直接控制燃油和空气的混合从而影响缸内燃烧过程。在此研究了进气道CFD分析方法,通过AVL-FIRE软件,建立进气道三维几何模型,生成网格模型,并进行求解计算出在不同气门升程下的气道流量系数和涡流/滚流比,最终通过优化流量系数同时权衡涡流/滚流比,实现发动机快速稳定的燃烧。     

环状阀流量系数影响因素数值研究

采用计算流体力学软件FLUENT,对不同环状阀做流场模拟计算,得到6条环状阀流量系数α,与升程和通道宽度比H／b的关系曲线。通过理论分析及对比各模拟曲线,分析了升程、阀座通道宽度和密封边宽度对流量系数的影响。模拟曲线相比实验曲线具有更大H／b范围,且考虑了阀座通道宽度和密封边宽度对曲线的影响,可以更好地指导压缩机环状阀的设计。     

煤气化核心调节阀的数值模拟与结构优化

该文以航天煤化工系统中的某型号笼式调节阀为研究对象,应用CFD数值模拟方法研究了调节阀的内流场特性。通过模拟给定压差下阀门不同开度的流量特性,得到调节阀的流量特性曲线,并与试验测定的数据进行比较分析,模拟值与试验值吻合较好。根据流场特性对流道做了优化并对新结构做了数值模拟,结果表明,优化后的流道流阻减小、涡流强度减弱、进而减少了能量损失。     

汽轮机凝汽器冷却水流量的在线测量方法研究

凝汽器冷却水流量对汽轮机运行经济性和安全性产生很大的影响,冷却水流量的在线测量目前尚无成熟的方法。提出借助于冷却水管路与凝汽器之间的连接弯管对冷却水流量进行在线测量。首先对流体在弯管内流动的自由涡流理论和强制涡流理论进行了分析,给出了弯管的理想流量与弯管内外压差之间的关系式。然后借助于数值模拟软件FLUNT,对流体在弯管前后以及弯管中流动过程中的速度和压力分布进行了数值模拟,指出弯管前后流体的速度和压力分布的不均匀性比较小。最后,以某300MW汽轮机为例,研究通过弯管流量与弯管内外压差之间的关系。结果表明,尽管进入凝汽器的冷却水弯管前后直管段均较短,但其流量系数随流量变化基本不变。从而证明可以借助于冷却水管路弯管内外压差实现对冷却水流量的在线测量。     

迷宫式调节阀流量特性的数值模拟

为了研究迷宫式调节阀的流量特性,利用CFD方法对其内部流场进行了模拟,得到流场中压力和速度分布,计算流量系数并得到流量特性。模拟试验结果表明迷宫流道结构能达到均匀降压,调节阀流量特性为线性,符合预期目标。     

发动机不同气门升程下气道及缸内流场分析

介绍了发动机螺旋进气道参数化设计的方法,使用Pro/E软件建立了螺旋进气道的三维模型,实现了螺旋进气道在不同气门升程下的参数化设计。应用Star-CD分析软件对螺旋进气道内的气体流动进行数值模拟计算,得到不同气门升程下气道及缸内流体的速度场和压力场分布图,计算出螺旋进气道的涡流比和流量系数,可以为螺旋进气道的改进设计提供指导。     

压缩机环状阀流量系数数值研究

应用计算流体力学软件FLUENT对环状阀流场进行模拟,得到流量系数αv与气阀升程和阀座通道宽度比H/b的关系曲线.使用MATLAB拟合得到流量系数计算公式.计算公式清晰地反应了升程和阀座通道宽度对流量系数的影响情况,使得环状阀流量系数的计算方便、快捷.     

叶片式水力旋流器操作参数优选

采用CFD软件中基于各相异性的雷诺应力湍流模型,应用PC-SIMPLEC算法,对叶片式旋流分离器内部流场进行了全面深入的三维数值模拟,得到了旋流器内部流场的压力分布特性和油相体积分数分布特性。通过数值模拟和试验研究,对旋流器的操作参数进行了优化,分析了不同分流比和流量对分离效率的影响,并最终优选出最佳分流比和最佳操作流量。     

Development of a new system for measuring the swirl ratio of an engine cylinder head under an unsteady flow condition

A new impulse-type swirl meter that measures the swirl ratio (R_s) and flow coefficient (C_fmean) during an intake air process for the intake port of an engine cylinder head under unsteady flow conditions was developed. The camshaft of the cylinder head was directly rotated by a step motor, allowing the valve lift to be adjusted automatically with the camshaft profile in the newly developed swirl measurement system. The measurements of the swirl ratio and flow coefficient were automated using a FPGA-DAQ board and a computer. The rotational speeds of the camshaft were held constant at steps of 90, 120, 150, 180 and 210 rpm during the measurement. As the camshaft rotation speed increased, the values of R_s tended to decrease while those of C_fmean tended to increase, implying that R_s and C_fmean depend on the engine speed. These results should be considered in the design of an intake port. With the newly developed swirl measurement system, it is possible to measure R_s and C_fmean repeatedly in a very short time. The repetitive measurement results of R_s and C_fmean were statistically processed. Through an uncertainty analysis, the values of the upper and lower bounds of R_s and C_fmean can be calculated for each camshaft rotation speed.

     

Investigation of in-cylinder flow patterns in 4 valve S. I. Engine by using single-frame particle tracking velocimetry

The in-cylinder flow field of gasoline engine comprises unsteady compressible turbulent flows caused by the intake port, combustion chamber geometry. Thus, the quantitative analysis of the in-cylinder flow characteristics plays an important role in the improvement of engine performances and the reduction of exhaust emission. In order to obtain the quantitative analysis of the in-cylinder gas flows for a gasoline engine, the single-frame particle tracking velocimetry was developed, which is designed to measure 2-dimensional gas flow field. In this paper, influences of the swirl and tumble intensifying valves on the in-cylinder flow characteristics under the various intake flow conditions were investigated by using this PTV method. Based on the results of experiment, the generation process of swirl and tumble flow in a cylinder during intake stroke was clarified. Its effect on the tumble ratio at the end of compression stroke was also investigated.     

Steady-flow characteristics and its influence on spray for direct injection diesel engine

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.     

A study on in-cylinder flow field of a 125cc motorcycle engine at low engine speeds

The in-cylinder flow characteristics of a four-stroke, four-valve, pent-roof small engine of motorcycle at engine speeds from 2000 rpm to 4000 rpm were studied using computational fluid dynamics (CFD). The aim of this study was to investigate the in-cylinder flow characteristics of small engines, including tumble, swirl, turbulent kinetic energy (TKE), angular momentum, in-cylinder air mass, turbulent velocity, turbulent length scale, and air flow pattern (in both intake and compression strokes) under motoring conditions. The engine geometry was created using SolidWorks, then was exported and analyzed using CONVERGE, a commercial CFD method. Grid independence analysis was carried out for this small engine and the turbulence model was observed using the renormalized group (RNG) k-ɛ model. The pressure boundary conditions were used to define the fluid pressure at the intake and exhaust of the port. The results showed that the increase in the engine speed caused the swirl flow in the small engine to be irregularly shaped. The swirl flow had a tendency to be stable and almost constant in the beginning of the compression stroke and increased at the end of compression stroke. However, the increase of in engine speed had no significant effect on the increase in tumble ratio, especially during the intake stroke. There was an increase in tumble ratio due to the increase in engine speed at the end of compression stroke, but only a marginal increase. The increase in engine speed had no significant effect on the increase in angular momentum, TKE, or turbulent velocity from the early intake stroke until the middle of the intake stroke. However, the angular momentum increased due to the increase in engine speed from the middle of the intake stroke to the end of compression stroke, and the angular momentum achieved the biggest increase when the engine speed rose from 3000 to 4000 rpm by 10 % at the end of the intake stroke. The increase in engine speed caused an increase of TKE and turbulent velocity from the middle of intake stroke until the end of compression stroke. Moreover, the biggest increase of TKE and turbulent velocity occurred when the engine speed rose from 3000 to 4000 rpm at the middle of intake stroke around 50 % and 25 %, respectively. Turbulent length scales appeared to be insensitive to increasing engine speed, especially in the intake stroke until 490 °CA. From that point, the value of the turbulent length scale increased as engine speed increased. The biggest increase in the turbulent length scales occurred when the intake valve was almost closed (around 20 %) and the engine speed was within two specific ranges (2000 to 3000 rpm and 3000 to 4000 rpm). Regarding the effect of engine speed, there were no significant effects upon the accumulated air mass in the small engine. The increase in engine speed caused an increase of turbulence in the combustion chamber during the late stages of the compression stroke. The increase in turbulence enhanced the mixing of air and fuel and made the mixture more homogeneous. Moreover, the increase in turbulence directly increased the flame propagation speed. Further research is recommended using a new design with several types of intake ports as well as combinations of different intake ports and some type of piston face, so that changes in air flow characteristics in small engines can be analyzed. Finally, this study is expected to help decrease the number of experiments necessary to obtain optimized systems in small engines.

     

Experimental study on axial stratification process and its effects (I)-Stratification in Engine-

This paper is the first of several companion papers, which investigate axial stratification process and its effects in an SI engine. The axial stratification is very sophisticate phenomenon, which results from combination of fuel injection, port and in-cylinder flow and mixing. Because of the inherent unsteady condition in the reciprocating engine, it is impossible to understand the mechanism through the analytical method. In this paper, the ports were characterized by swirl and tumble number in steady flow bench test. After this, lean misfire limit of the engines, which had different port characteristic, were investigated as a function of swirl ratio and injection timing for confirming the existence of stratification. In addition, gas fuel was used for verifying whether this phenomenon depends on bulk air motion of cylinder or on evaporation of fuel. High-speed gas sampling and analysis was also performed to estimate stratification charging effect. The results show that the AFR at the spark plug and LML are very closely related and the AFR is the results of bulk air motion.     

收缩形预旋喷嘴流场的实验研究

采用实验的方法,在一个不包含转动件的静腔系统中,对预旋进气角度为30°的收缩喷嘴和预旋进气角度分别为30°,25°,20°的非收缩预旋喷嘴特性进行研究,得到了喷嘴收缩和预旋角度对预旋喷嘴出口流场的影响。实验结果表明,相对于非收缩喷嘴,收缩喷嘴可以提高出气全速度,降低出气全速度不均匀系数,提高周向出气速度,这有利于冷却效率的提高;预旋角度的减小也有利于提高冷却效率。     

A study on the characteristics of in-cylinder intake flow in spark ignition engine using the PIV

In this study, to investigate m-cyhnder tumble or swirl intake flow of a gasoline engine, the flow characteristics were examined with opening control valve (OCV) and several swirl control valves (SCV) which intensify intake flow through steady flow experiment, and also turbulent characteristics of m-cyhnder flow field were investigated by 2-frame cross-correlation particle image velocimetry (PIV) method In the investigation of intake turbulent characteristics using PIV method, the different flow characteristics were showed according to OCV or SCV figures The OCV or SCV installed engine had higher vorticity and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder Above all, SCV B type was superior to the others About energy dissipation and reynolds shear stress distribution, a baseline engine had larger loss than OCV or SCV installed one because flow impinged on the cylinder wall It should be concluded, from what has been said above, as swirl component was added to existing tumble flow adequately, it was confirmed that turbulent intenstty was enlarged, flow energy was conserved effectively through the experiment In other words, there is a suggestion that flow characteristics as these affected to m-cyhnder combustion positively     

The experiments for the enhancement of regression rate of hybrid rocket fuel

Many studies have been conducted to increase regression rate of solid fuel in hybrid rocket. One of them resorts to swirl flow since it can extend the residence time of oxidizer in the fuel grain. Also, metal wires may lead to increase the regression rate of solid fuel as shown in solid propellants. In this study, a series of experiments was designed to investigate the enhancement of regression rate of solid fuel by embedded metal wires and by fuel port grain. And fuel port was designed with a helical configuration to attempt to induce swirl flow. PMMA with gaseous oxygen is the solid fuel used for investigation. Test results showed that embedded metal wires turned out to be ineffective method because only 3-4% increases in regression rate were observed. However, fuel port grain configuration yields higher burning performance of up to 50% increase in regression rate. Also pitch number as well as total impulse was found to be a design variable.     

喷水减温阀离心喷嘴雾化性能的优化研究

为了探索喷水减温阀喷嘴结构参数变化对其雾化效果的影响,优化喷嘴结构参数,根据Fluent软件VOF模块对喷水减温调节阀的离心喷嘴进行气-液两相仿真分析。以喷嘴出口直径、旋流槽倾斜角、旋流室收缩角作为优化因素,以雾化锥角、流量系数作为雾化性能的评价指标,进行正交实验设计。基于响应面法建立雾化锥角和流量系数的代理模型,再运用粒子群优化算法对代理模型进行寻优,得到一个最优结构参数。结果表明:当出口直径为2.55 mm,旋流槽角度为40°,旋流室角度为110°时,雾化性能得到最优,雾化锥角比原模型增大17.7％,流量系数增大32.53％,为喷嘴的设计提供了一个新的方案。     

单螺杆压缩机几何参数对压缩机性能的影响

根据单螺杆压缩机的结构特点和工作过程特性,分析了单螺杆压缩机中啮合副的几何参数对压缩机性能的影响。计算了不同中心距系数和星轮螺杆直径比情况下压缩机的排气量,排气孔口位置和面积以及在排气孔口位置保持不变的情况下的流动损失情况。通过分析发现:排气量随星轮螺杆直径比的增大而增大,而随中心距系数的增大呈先增大后减小的趋势。排气开始位置不受星轮螺杆直径比变化的影响,只随中心距系数的增大而往排气侧延迟,排气孔口面积则随星轮螺杆直径比的增大而增大。在排气孔口位置不变的情况下,随星轮螺杆直径比增大,排气过程的流动阻力损失线性增加。该分析结果为压缩机改型设计提供了依据。