【作者】 李萍；

【导师】 张薇；

【作者基本信息】 南京工业大学 ， 材料加工工程， 2006， 硕士

【摘要】 燃油的分裂与雾化过程实际上是液体射流的一种失稳现象,在工程上常常利用射流的这种失稳过程来实现燃油的雾化,以增加燃油的表面积提高燃烧效率。因此对液体射流分裂与雾化机理的研究不仅具有重要的理论意义,而且还具有深远的工程应用背景。近年来发展起来的计算流体力学(CFD)技术与具体工程问题相结合不仅可以节省大量的人力物力,提高实验效率,而且还可以得到实验无法得到的详细信息, CFD技术在结构设计和优化方面的应用越来越受到人们的重视。本文主要是利用专业CFX软件,采用计算成本不是很高,同时具有一定精度的粘度模型即RNG k-ε模型,对柴油喷雾特性进行模拟研究。柴油机燃油喷射雾化过程不仅受喷嘴结构形式和工作参数的影响,还受温度、气流运动等诸多因素的影响。本文对粘性液体射流分裂与雾化过程的机理进行了理论和数值研究,并将结果应用于柴油喷嘴雾化工作过程的模拟中,具体完成了以下几方面的工作:概括总结了前人关于射流稳定性及其分裂雾化机理的研究成果,同时对内燃机工作过程中,燃油的雾化模型进行了介绍,综述了计算流体力学的发展、特点和具体工作步骤,分析了湍流流动的特点,引出了选题的目的及意义;概述了计算流体动力学的有关知识,建立和选择了几何模型和数学模型,确定了合适的物理模型,对柴油的喷雾过程进行了具体数值计算,获得了较好的模拟结果,如喷嘴内、外速度场、压力场和柴油浓度场的分布;对喷嘴在不同参数条件下进行了大量雾化特性试验,分析研究了气液交角、喷孔直径等几何参数,气液比、油速、气速、压力等工况参数和液体性质等对雾滴索特平均直径(SMD)的影响规律,并把模拟计算值和理论值进行比较。通过理论分析和模拟研究,找出了影响雾化喷嘴雾化性能的主要因素;根据流体的流动特性,得出了雾化喷嘴的流体参数、喷嘴结构尺寸与雾化特性之间的关系,并将结果应用于喷嘴的设计中;自行设计了一种内混式蒸汽雾化器喷嘴。由于目前人们未能总结出各种结构参数对雾化质量影响的定量关系,喷嘴的设计还是主要依靠实验来解决,本文突破了只有用实验和测试手段才能得到雾化质量的传统方法,直接通过模拟和计算相结合的办法,对喷嘴的各项雾化指标进行的测定,既节省了人力、物力,还可以更直观地了解到喷嘴结构尺寸对雾化的影响趋势,对喷嘴的定型设计提供了依据。雾化喷射是一种复杂的过程。模拟结果与雾化理论机理对比取得较好的一致,说明本更多还原

【Abstract】 In fact, the process of fuel breakup and atomization is a kind of instability phenomenon of the liquid jet. In order to increase the oil surface area and promote efficient combustion, the instability process of the jet is always used to make the fuel atomization in engineering. So study on the mechanisms of breakup and atomization of liquid is not only important on theory, but also owns the engineering background.Being used to analyze the flow, mixing and mass transfer characters of fluid, Computational Fluid Dynamics (CFD) can not only save a lot of resource, but also get some important local data that cannot be gathered in experiment. Now CFD technology is regarded more and more in the fields of the design and optimization. The article mainly uses the professional software-CFX and adopts the viscosity models, i.e. RNG k-εmodel, which can be suitable, with moderate cost, to simulate the atomizing characteristics.The injection and atomization process is dynamic, which is not only affected by the nozzle configuration and injection pressure, but also affected by the temperature, pressure, gas flow. This thesis conducts a theoretic and numerical investigation on the mechanisms of the breakup and atomization of viscous liquid jets, and the results obtained from this studying are applied in the process simulation in internal mix sprayer. The following terms have been finished: the detailed review of the previous works on the stability analysis of liquid jets and it’s breakup and atomization are given, in addition, the fuel atomization models are introduced in this dissertation, introduce the development, characters and working steps of CFD, analyze turbulence characteristics, educe the intention and the signification of the article; generalize the knowledge about CFD,establish the geometry model and choose the mathematics model,ensure appropriate physics model, put up appropriate physical model,simulate the process of the atomization of the diesel oil , gain the good simulation results, such as distributing of the velocity field, pressure field and diesel oil density concentration field. Then the study about the spray characteristics of internal mixing atomizer is obtained. Many factors such as air-liquid angle, outlet diameter geometrical size, air-liquid rate, oil velocity, air velocity, pressure operating condition and liquid更多还原