液雾碰壁对环形喷嘴雾化质量的影响

本文应用于基于激光衍射原理手瞬变喷雾场粒径分布测量系统，进行了液雾碰壁对环形喷雾雾化质量影响的实验研究，对液滴壁过程进行了理论分析，并提出了个液滴碰壁模型。     

直喷式柴油机燃烧室形状对碳粒形成过程影响的试验研究

本文介绍了作者采用可视化技术和图象分析技术研究直喷式柴油机燃烧室形状对燃烧室内喷雾场和燃烧碳粒场影响的研究结果。分析了四角形燃烧室和盆形燃烧室喷雾发展历程和燃烧碳粒场发展历程，找出了四角形燃烧室碳粒排放量较低的原因。     

模型饱和器冷态喷雾场的实验研究

针对HAT循环关键部件增湿饱和器内典型的传热，传质过程现象，为了最优化该过程和为今后数值分析提供有效的数据，设计了模拟饱和顺内传热，传质过程中的开放式冷态实验系统。使用相位多普勒分析仪DualPDA（Phase Doppler Analyzer）对冷态模型饱和器的喷雾场进行了详细的实验研究，测量了不同水压，不同气流速度下的喷雾场，得到喷雾场内液滴的三维平均速度分布，脉动速度分布，平均粒径大小分布等，分析了喷雾水压和鼓风气流速度对喷雾场的影响，分析结果表明，改良设计的离心喷嘴具用良好的喷雾性能和轴对称性，水压增大可以增大喷雾场中粒子速度，通量及降低平均直径，喷嘴喷雾长度随气流速度减小，气流速度可以改变喷雾场的分布，有利于液滴蒸发和液滴破裂。     

供油提前角对直喷式柴油机喷雾、燃烧和碳粒变化历程的影响

介绍了采用同步双成像技术研究供油提前角对直喷式柴油机喷雾、燃烧和碳粒变化历影响的研究结果。研究结果表明：增大供油提前角时,着火会发生在燃油停止喷射后。停喷后着火和停喷前着火相比,其着火瞬间的喷雾场和此后的燃烧场、碳粒场的变化历程有明显不同。增大供油提前角可以减少燃烧过程前期的碳粒生成量,进而降低碳粒排放。     

GDI喷油器喷雾碰壁的基础试验研究

为了研究直喷汽油机喷雾碰壁可能导致的机油稀释与碳烟排放增加问题,对某款直喷汽油机喷油器进行改造,使用相位多普勒激光测试系统(phase Doppler analyzer,PDA)研究了不同壁面条件下,近壁面处喷雾液滴的粒径分布与法向速度分布特点。研究结果表明:碰壁过程对距壁面较近的液滴径向发展有显著影响,自由喷雾表现为由轴线向外液滴特征粒径减小,而喷雾碰壁则为增大趋势;壁面温度对液滴粒径概率分布和法向速度分布影响显著,壁面加热条件下粒径集中于10μm范围内,而绝大多数液滴法向速度趋近于0;壁面干湿条件的影响主要表现在粒径概率分布、特征粒径径向发展和法向速度分布,粒径概率分布形态产生变化,特征粒径径向发展呈现为由轴线向外先减小后略有增大的趋势,法向速度在10~30m/s范围内的液滴数量明显减小。此外,碰壁位置是影响液滴分布的关键因素,碰壁位置距喷嘴越远,液滴粒径分布越趋向均匀。     

不同燃料喷雾撞壁后液滴破碎过程

运用相位多普勒激光测试(PDA)系统对汽油、异辛烷、甲醇和乙醇的自由喷雾以及喷雾撞壁后的粒径和粒速分布分别进行试验,并根据理论模型对不同燃料撞壁后的飞溅比例进行预测.结果表明:甲醇与乙醇自由喷雾液滴直径明显大于汽油和异辛烷,多集中于10～30,μm范围,且在相同的喷射条件下更容易产生撞壁飞溅和二次破碎.喷雾内部液滴运动状态差别极大,在R8(喷孔轴线为8,mm)位置更易产生飞溅破碎,其中甲醇与乙醇在R8处飞溅比例分别为55.9%,和56.7%,,而汽油和异辛烷仅为49.7%,和49.1%,.反射液滴直径由于飞溅破碎作用相比自由喷雾明显减小,且使喷雾中心区域的入射液滴更容易产生碰撞与相互作用.自由喷雾和入射喷雾边缘部分液滴法向速度分布较中心更为分散.乙醇自由喷雾边缘切向速度大于汽油,而入射液滴相反.     

基于X射线同轴相衬成像技术的喷雾场研究

介绍了一种全新的运用X射线同轴相衬成像技术对汽油机喷雾场进行研究的试验方法,并对其相衬成像的原理作了简介,理论分析了成像的可能性.通过分析试验所得的喷雾照片可知:X射线同轴相衬成像技术可以去除液滴微粒对传统可见光技术测量时光的散射、折射的影响,且能在不破坏喷雾场内部结构的基础上观察到喷雾场真实的内部结构,同时能够测得瞬态的喷雾场速度.该测试系统具有成像清晰、图形处理方便等特点.     

燃烧室内喷雾两相流场数值研究

采用贴体曲线网格、RNG k-e湍流模型和随机轨道法计算了火焰筒内的喷雾两相流动,构造了包括旋流器在内的主燃烧室计算网格,计算了5种旋流器下的主燃烧室的气流场和喷雾场,分析了不同旋流器对喷雾场和气流场的影响,以及喷雾对气流场的影响,并与实验结果进行了对比。结果显示旋流器叶片角度增大或者外内旋流器流量比的增加,都会导致液滴的喷雾锥角增大。喷雾使气流场的速度减小,旋流强度降低,随着旋流器叶片角度增加或者外内旋流器流量比的增加,喷雾场对气流场的影响增大。提出了主燃烧室内旋流器设计的改进方案。     

LPG碰壁喷雾的试验及数值模拟研究

基于离散液滴模型(DDM),并结合柴油机实际工作情况,建立了喷雾碰壁的数学模型.将该模型与KIVA程序耦合,对多种形态的喷雾碰壁进行了模拟计算.在压力定容室内,利用PIV高速摄影技术对液化石油气(LPG)和柴油的碰壁喷雾过程进行了试验研究.将模拟与试验结果进行了对比分析,并着重考察了碰壁角度对燃料碰壁过程的影响,获得了LPG喷雾碰壁特性的一般规律.与柴油相比,在同样条件下,LPG能在壁面上溅起较厚的液滴雾层,且溅起的液滴尺寸较小,在壁面上附着的油膜厚度较薄,说明LPG比柴油蒸发速度快,雾化质量好;随着碰壁喷雾倾斜角的增大,2种燃料在碰撞点壁面附近所产生的液滴数显著减少.     

撞击式喷雾特性的拉格朗日数值模拟

采用数值模拟的方法对自由喷雾和撞击式喷雾特性展开研究.在开源CFD程序KIVA-3V的基础上,嵌入改良的环境压力表征的液滴碰撞模型,对1 MPa和6 MPa下自由喷雾与撞击式喷雾喷射过程中的液滴碰撞频率、索特平均直径(SMD)等微观特性进行研究.结果表明:低压环境(1 MPa)下撞击式喷雾的液滴碰撞后融合频率较高,其SMD较自由喷雾偏大;随着压力升高,液滴碰撞后表现出以"弹开"为主的结果,高压环境(6 MPa)下撞击式喷雾相比自由喷雾会有更小的SMD,更有利于随后的雾化与燃烧过程.在此基础上继续研究喷油量对撞击式喷雾雾化特性的影响,进一步发现了高压环境下空气阻力和环境压力诱导的液滴弹开行为主导了撞击式喷雾的微观特性,为今后直喷式内燃机供油系统的改进提供了参考.     

Direct numerical simulation of ignition in turbulent n-heptane liquid-fuel spray jets

Direct numerical simulation was used for fundamental studies of the ignition of turbulent n-heptane liquid-fuel spray jets. A chemistry mechanism with 33 species and 64 reactions was adopted to describe the chemical reactions. The Eulerian method is employed to solve the carrier-gas flow field and the Lagrangian method is used to track the liquid-fuel droplets. Two-way coupling interaction is considered through the exchange of mass, momentum, and energy between the carrier-gas fluid and the liquid-fuel spray. The initial carrier-gas temperature was 1500 K. Six cases were simulated with different droplet radii (from 10 to 30 μm) and two initial velocities (100 and 150 m/s). From the simulations, it was found that evaporative cooling and turbulence mixing play important roles in the ignition of liquid-fuel spray jets. Ignition first occurs at the edges of the jets where the fuel mixture is lean, and the scalar dissipation rate and the vorticity magnitude are very low. For smaller droplets, ignition occurs later than for larger droplets due to increased evaporative cooling. Higher initial droplet velocity enhances turbulence mixing and evaporative cooling. For smaller droplets, higher initial droplet velocity causes the ignition to occur earlier, whereas for larger droplets, higher initial droplet velocity delays the ignition time.     

Experimental investigations of spray generated by a pressure swirl atomizer

This paper has focused on the droplets behavior of kerosene RP-3 spray produced by a pressure swirl atomizers in terms of spray pattern, droplet size spatial distribution, mean droplet size, and distribution index with variations of pressure differential. The analyses have been carried out experimentally with the aid of optical diagnostic methods. The spray pattern, such as spray cone angle and fuel spatial distribution, has been measured by the technique of planar laser induced fluorescence of kerosene. A method for correction of fuel distribution measurement error induced by laser attenuation in spray is proposed and validated. The droplet size spatial distribution in central axis plane of the spray has been measured by a planar droplet sizing method which combining laser induced fluorescence and Mie scattering. The spray pattern in axial center plane and cross-sectional plane perpendicular to axis of the atomizer indicate that the droplets in spray concentrate around the outer periphery and in a narrow annular zone at the near-field of fuel injector exit, and then disperse to produce a solid spray at downstream of the spray. The analyses of droplet size spatial distribution, Sauter mean diameter, and distribution index with pressure differential clearly show the presence of droplets collision and its adverse effects on droplet size uniformity. The spray outline, droplet mass spatial distribution, and droplet size spatial distribution, droplets dispersion and collision in the process of atomization provide a great insight into the processes of atomization and spray development, which are key information for fuel injector design and quality control. The visualizations of spray pattern and droplet size spatial distribution with variations of pressure differential for pressure swirl atomizer are key issues in swirl cup or internally staged airblast fuel injectors because pressure swirl atomizer provides primary atomization or pilot spray which affects the quality of air/fuel mixing in lean-burn combustion. Moreover, a well-defined and complete database regarding the isothermal hollow cone spray is provided for validation of spray model.     

空心喷雾油滴碰撞热多孔介质的数值研究

为加深对多孔介质发动机中均匀混合气形成的了解,用改进的KIVA-3V详细模拟了空心喷雾油滴碰撞热多孔介质的过程。在KIVA-3V中增加了油滴碰撞热多孔介质壁面的碰撞模型、传热模型及空心喷雾的线性不稳定性液膜破碎(LISA)模型。油滴与热壁的碰撞模型和传热模型经检验证明了其合理性。在简化多孔介质结构的基础上,在不同的环境压力及喷雾锥角下,模拟了空心喷雾与热多孔介质的相互作用。计算结果表明:油雾在碰撞到热多孔介质后,发生分裂的油束和多孔介质区域的高温,促使油滴实现快速蒸发并为油蒸汽与空气充分混合创造了前提。不同的空间压力及喷雾锥角直接影响到油滴在多孔介质中的分布。     

The effect of ionisation of spray in cooling air on the wetting characteristics of finned tube heat exchanger

A major concern when introducing a water spray to pre-cool the air flowing into a finned tube heat exchanger is that wetting of the heat exchanger surface may cause corrosion. In an attempt to prevent droplets from impacting and wetting the heat exchanger, the use of an electrostatically charged spray was investigated. Experiments were performed whereby electrostatically charged spray was sprayed on a heat exchanger with an electric charge having the same polarity as the droplets. The results indicated that droplet deposition decreased significantly as the charge on the droplets was increased. However, total prevention of deposition could not be achieved, since the equipment used could not produce high enough voltages. This concept shows some promise, and it is recommended that further research be performed on it.     

燃油喷射雾化机理的探讨

本文从空气动力干扰假说出发，通过分析油－气交界面上不稳定波波幅增长和破碎过程，定性和定量地探讨了索特平均直径及滴径分布。本文认为，燃油雾化过程可分为两阶段：一次雾化和二次雾化。一次雾化只发生在油－气交界面上，主要是喷注和空气之间的气动干扰作用，由射流表面产生不稳定波波幅增长和破碎所引起的；而二次雾化则发生在油气渗混区，由一次雾化后产生的油滴在空气中进一步破碎和相互聚合来决定。算例表明，燃油二次雾化假设及其对索特平均直径ＳＭＤ和滴径分布所作的定量分析是一次成功的尝试。     

Numerical investigation of the effects of fuel spray type on the interaction of fuel spray and hot porous medium

The interaction between two types of fuel spray and a hot porous medium is studied numerically by using an improved version of KIVA-3V code. The improved KIVA-3V code is incorporated with an impingement model, a heat transfer model and a linearized instability sheet atomization (LISA) model to model the hollow cone spray. An evaporating fuel spray impingement on a hot plane surface was simulated under conditions of experiments performed by Senda to validate the reasonability of the KIVA-3V code. The numerical results conform well with experimental data for spray radius in the liquid and the vapor phases. Computational results on the interaction of two types of the fuel spray and the hot porous medium show that the fuel spray can be split, which provides conditions for quick evaporation of fuel droplets and mixing of fuel vapor with air. The possibility of fuel droplets from hollow cone spray crossing the porous medium reduces compared with that from solid cone spray, with the same initial kinetic energy of fuel droplets in both injection types.     

Spherical-shaped ice particle production by spraying water in a vacuum chamber

A theoretical and experimental study was performed to examine the water spray evaporation method for ice particle production. The conditions for the formation of ice particles were investigated theoretically by the diffusion-controlled evaporation model. The prediction by the model was proved to agree relatively well with experiments. The production of cold storage heat will increase almost proportionally to the number of spray nozzles because no substantial difference was found in the mean droplet size of the overlapped sprays from twin nozzles. Finally, based on the results, the vacuum chamber was designed, and spherical ice particles of size below 300 μm were experimentally obtained by spraying water droplets of ambient temperature in the vacuum chamber where pressure is maintained below the freezing point of water. From the experiment for producing ice particles, it was found that the spray flow rate influences the performance of the system more than the position of spray nozzle.     

伞喷油雾与热多孔介质相互作用的数值模拟

为深入认识多孔介质发动机中均匀混合气的形成，用改进的KIVA-3V详细模拟了伞喷油雾与热多孔介质之间的相互作用．在KIVA-3V中增加了油滴碰撞热多孔介质壁面的碰撞模型、传热模型．为检测数值模型的合理性，在Senda等人的实验条件下进行了数值计算．油束碰壁后油滴和油蒸气分布的数值计算结果与实验结果吻合较好．在简化多孔介质结构的基础上和不同的环境压力及喷雾锥角时，模拟了伞喷油雾与热多孔介质的碰撞过程．计算结果表明，伞喷油雾的喷雾锥角及空间压力对油滴在多孔介质中的分布有着很大的影响，在多孔介质厚度一定时，通过调节这些参数，能够形成均匀混合气．     

多流体碱雾发生器内蒸发喷雾射流的数值模拟

通过对多流体碱雾发生器中伴随气固两相流的蒸发喷雾射流的数值模拟,得到了碱雾发生器内气液固三相的速度矢量场.计算结果表明,气体轴向速度呈中间高两头低的对称分布;对于不同粒径的液滴,呈现出不同的空间分布规律,大液滴由于惯性大,可以穿越周围的气流区,比小液滴有更大的扩展角;在喷嘴出口2倍管道直径区域,由于雾化液滴与固体颗粒存在较大的速度差,有利于固体颗粒的碰撞增湿.     

NUMERICAL MODELING FOR INTERACTION OF A WATER SPRAY WITH SMOKE LAYER

Interaction of a water spray with a smoke layer was studied numerically. A one-dimensional model was developed by taking smoke and air as two quasi-steady layers. W ater droplets of the spray were divided into several typical classes based on the droplet distribution function. Spray characteristics such as droplet diameter and velocity, shape of the spray envelope, gas temperature, and flow rate inside the spray envelope were calculated with heat and mass transfer to the induced air flow. The simulated results agreed with the experiments on full cone water spray in a normal atmospheric environment, and indicated some physical principles for using water spray to minimize smoke damage.