直喷汽油机中空锥形燃油喷雾的雾化和蒸发模型

高压旋流中空燃油喷雾日益广泛地应用于缸内直喷(GDI)汽油机中，为此发展了一种适合于模拟这种燃油喷雾雾化过程的薄膜喷雾模型．燃油薄膜的破碎过程采用表面波破碎理论来模拟．对Spalding蒸发模型和油滴阻力模型进行了改进，用来计算油滴的蒸发和阻力变形过程，同时引入初始喷雾液团的计算模块．在多维内燃机计算程序KIVA3的基础上建立了改进的数值计算模型，并对不同喷射条件下的定容压力容器中空旋流燃油喷雾过程进行了数值计算，对计算和实验所得的喷雾特性包括油束外形结构，油束喷雾贯穿度和油滴粒径进行了详细的比较，同时对单液滴的蒸发过程也进行了数值计算，油束模型的计算结果与实验结果吻合良好。     

涡流室式柴油机燃油蒸发过程的三维数值模拟

建立了高温高压条件下的油滴蒸发模型,并在不同的工质压力和温度下对模型进行了验证,模型计算结果和实验结果吻合良好。将此油滴蒸发模型和油膜蒸发模型相结合,应用到涡流室式柴油机的燃油蒸发过程中,通过三维数值模拟计算,研究了燃油蒸发过程中燃料蒸气浓度和工质温度场的变化历程以及燃油蒸发对涡流室平均温度和平均压力的影响。     

不同来流温度下单液滴燃烧的数值模拟

单液滴蒸发燃烧规律是研究喷雾蒸发与燃烧这一复杂物理化学过程的基础.与传统折算薄膜理论相比,从基本控制方程出发,建立了高温对流环境中单液滴的瞬态蒸发与燃烧模型.模型中详细考虑了液相内部环流、气相边界层流动以及热物性的变化,并采用数值模拟方法分析了来流温度对油滴蒸发燃烧特性的影响.计算结果复现了实验中液滴火焰由尾部火焰向包覆火焰的发展过程,验证了直径平方定律的适用范围,并得到了来流温度对油滴蒸发燃烧特性的影响规律.     

柴油机喷雾蒸发混合和燃烧的数值模拟

应用一个准维多区模型对柴油机喷雾的蒸发、混合和燃烧进行了数值模拟,提出了求解燃油蒸发过程的油滴直径瞬时变化的简单代数方程,考虑了碰壁对喷雾射流贯穿的影响。并对一台直喷式柴油机的燃烧过程进行了计算,计算结果与试验值符合较好。     

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。     

液滴蒸发一维数学模型及其在二甲醚喷雾中的应用

描述了液滴蒸发的一维数学模型及其数值求解方法,并且利用该模型首先对单液滴的蒸发过程和定容燃烧室内二甲醚(DME)的喷雾过程分别进行了模拟计算和分析,然后对二甲醚发动机的喷雾燃烧过程进行了数值模拟,并将模拟结果与KIVA程序中原有的Spalding蒸发模型及实验数据进行了对比.结果表明,一维蒸发模型对蒸发过程的描述较Spalding的零维蒸发模型更为真实.     

高温环境下二甲基醚(DME)喷雾特性的实验研究

对二甲基醚（DME）在高温条件下的喷雾特性进行了实验研究。结果结果表明：与常温条件相比，DME喷雾体喷雾核心面积变小，喷雾体呈薄雾状发展，DME蒸发极为迅速；高温条件下喷油前期DME的嘴端压力比常温下小；在所实验的温度范围内，环境温度对喷雾体的贯穿距离没有影响；环境密度对喷雾体贯穿距离的影响也较小，环境密度增大时，贯穿距离略有减小。     

甲醇喷雾着火过程的化学动力学模拟

本文利用广安博之的喷雾分区模型与油滴蒸发速率模型相结合,给出燃烧室内燃油与空气的分布.依据实验数据,确定了含有18种组分、30步基元反应、适合于柴油机缸内条件的甲醇喷雾着火过程的化学动力学模型,能模拟燃烧室内甲醇喷雾自燃过程特征,用于对使用空气加热的纯甲醇压燃过程的滞燃期预测.结果表明,该模型能较成功地预测各种发动机工况下的着火滞燃期.     

瞬时蒸发特性对LPG雾化性能的影响

依据LPG沸点低的特点,在FIRE8.42软件平台下建立瞬时蒸发模型,模拟LPG自由喷雾过程,得到LPG缸内直接喷射的油滴尺寸、温度以及油滴的贯穿距等参数的特性。通过与试验结果对比,表明瞬时蒸发模型符合实际情况。     

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．     

Numerical simulation of fuel sprays at high ambient pressure: the influence of real gas effects and gas solubility on droplet vaporisation

This paper deals with the numerical simulation of the vaporisation of an unsteady fuel spray at high ambient temperature and pressure solving the appropriate conservation equations. The extended droplet vaporisation model accounts for the effects of non-ideal droplet evaporation and gas solubility including the diffusion of heat and species within fuel droplets. To account for high-temperature and high-pressure conditions, the fuel properties and the phase boundary conditions are calculated by an equation of state and the liquid/vapour equilibrium is estimated from fugacities. Calculations for an unsteady diesel-like spray were performed for a gas temperature of 800 K and a pressure of 5 MPa and compared to experimental results for droplet velocities and diameter distribution. The spray model is based on an Eulerian/Lagrangian approach. The comparison shows that the differences between the various spray models are pronounced for single droplets. For droplet sprays the droplet diameter distribution is more influenced by secondary break-up and droplet coagulation.     

乙醇液滴在高温氮气环境下的运动蒸发特性

为达到新型燃料发动机高效工作的目的,基于质量、动量、能量方程,对单个乙醇液滴在高温氮气环境下的运动和蒸发过程建立数学模型,通过与实验数据对比,验证了模型的有效性。分析了不同环境压力下,液滴温度、速度、尺寸与时间和贯穿距离的关系。结果表明：环境压力越高,瞬态和平衡蒸发阶段时间越长,温度越高;液滴运动速度下降越快,贯穿距离越短;蒸发速度越慢,液滴寿命越长。在液滴速度连续变化的距离内,液滴温度逐渐上升,而尺寸略有膨胀。随环境压力升高,瞬态阶段的膨胀越显著。     

Numerical simulation of emulsified fuel spray combustion with puffing and micro-explosion

The purpose of this study was to develop numerical simulation of spray combustion of emulsified fuel with considering puffing and micro-explosion. First, a mathematical model for puffing was proposed. In the proposed puffing model, the rate of mass change of a droplet during puffing was expressed by the evaporation rate of dispersed water and the mass change rate due to fine droplets spouted from the droplet surface. The mass change rate due to fine droplets was related to the evaporation rate of the dispersed water and each liquid content. This model had only one experimental parameter. The essential feature of this model was that it was simple to apply to numerical simulation of spray combustion. First, the validity of the proposed puffing model was investigated with the experimental results for a single droplet. The calculated results for a single droplet with the experimental parameter varying from 5.0 to 10 were in good agreement with the experimental results. Moreover, numerical simulation of spray combustion of emulsified fuel was carried out. The occurrence of puffing and micro-explosion was determined by the inner droplet temperature. When micro-explosion occurred, a droplet changed to vapor rapidly. When the proposed puffing model was used in numerical simulation of spray combustion, the experimental parameter in the puffing model was determined for each droplet by random numbers within the range 5.0-10. The calculated results of spray combustion of emulsified fuel without considering puffing or micro-explosions were different from the experimental results even where combustion reactions were almost terminated. Meanwhile, the calculated results when considering puffing and micro-explosions were in good agreement with experimental results at the same location.     

Investigation of heat and mass transfer between the two phases of an evaporating droplet stream using laser-induced fluorescence techniques: Comparison with modeling

Heat and mass exchanges between the two phases of a spray is a key point for the understanding of physical phenomena occurring during spray evaporation in a combustion chamber. Development and validation of physical models and computational tools dealing with spray evaporation requires experimental databases on both liquid and gas phases. This paper reports an experimental study of evaporating acetone droplets streaming linearly at moderate ambient temperatures up to 75 °C. Two-color laser-induced fluorescence is used to characterize the temporal evolution of droplet mean temperature. Simultaneously, fuel vapor distribution in the gas phase surrounding the droplet stream is investigated using acetone planar laser-induced fluorescence.Temperature measurements are compared to simplified heat and mass transfer model taking into account variable physical properties, droplet-to-droplet interactions and internal fluid circulation within the droplets. The droplet surface temperature, calculated with the model, is used to initiate the numerical simulation of fuel vapor diffusion and transport in the gas phase, assuming thermodynamic equilibrium at the droplet surface. Influence of droplet diameter and droplet spacing on the fuel vapor concentration field is investigated and numerical results are compared with experiments.     

快速降压环境下盐水液滴蒸发过程的传热传质研究

采用VOF（Volume of Fluid）自由表面捕捉方法对盐水液滴蒸发过程中气液界面进行追踪,建立了降压环境下单个盐水液滴的蒸发模型,并通过盐水液滴蒸发的实验数据验证了此模型。通过对盐水液滴在相变过程中的形态变化以及传热传质特性的分析,研究了液滴内部温度、速度、蒸汽分布以及液滴形态等随时间的变化情况,分析了影响盐水液滴降压蒸发过程的主要因素。结果表明：在降压蒸发过程中液滴形态变化和环境中蒸汽的分布会随速度场的变化而变化;蒸发过程中初始盐组分质量浓度越大的液滴蒸发速率越缓慢,最终能达到的液滴最低中心温度越高,且液滴中心温度回升速度越慢、回升时间也越晚;液滴初始温度对蒸发速率影响较大,初始温度越高,表面蒸发速率越快,液滴中心温度回升速度越快。     

二甲醚液滴高压蒸发的数值模拟

在分析燃油液滴高压蒸发规律的基础上,考虑液滴内部的热传导过程、内部环流和非理想气体效应,建立了高压蒸发模型,并利用该模型对二甲醚(DME)单液滴的蒸发过程进行了数值模拟分析。采用状态方程法计算了DME-N2体系的气液相平衡。结果表明:高压有利于燃料液滴蒸发;即使环境压力超过燃油的临界压力,其平衡蒸发温度也未必能达到临界温度。     

Large eddy simulations for radiation-spray coupling for a lean direct injector combustor

Large Eddy Simulations (LESs) for a lean-direct injection (LDI) combustor are performed and compared with experimental data. The LDI emissions characteristics, and radiation-spray coupling effect on the predictions are analyzed. The flamelet progress variable approach is employed for chemistry tabulation coupled with a stochastic secondary breakup model. Good comparisons are shown with the experimental data mean and root mean square for both the gas phase and spray droplets profiles. The effect of combustion is found to change the shape and structure of the central recirculation zone to be more compact in length but larger in diameter in the transverse direction. In-addition the results show that the gas phase radiation alters the spray dynamics by changing the local gas-phase temperature distribution. This impacts the spray evaporation rate, the local mixture fraction, and consequently the combustion heat released rate and the predicted emissions. The simulation with no radiation modeling shows over prediction in the temperature distribution, pollutants emissions, higher fuel evaporation rate, and narrower range of droplet size distribution with lower number density for the smaller size particles. The current study suggests that, even for low pressure systems, radiation modeling can be important for accurate emissions prediction.     

Heat and mass transfer of combusting monodisperse droplets in a linear stream

Heat and mass transfer phenomena in fuel sprays is a key issue in the field of the design of the combustion chambers where the fuel is injected on a liquid form. The development and validation of new physical models related to heat transfer and evaporation in sprays requires reliable experimental data. This paper reports on an experimental study of the energy budget, i.e. internal flux, evaporation flux and convective heat flux for monodisperse combusting droplets in linear stream. The evaporation flux is characterized by the measurement of the droplet size reduction by the phase Doppler technique, and the droplet mean temperature, required for the internal and convective heat flux evaluation, is determined by two-color, laser-induced fluorescence. The Nusselt and Sherwood numbers are evaluated from the heat and mass fluxes estimation, as a function of the inter-droplet distance. The results are compared to physical models available in the literature, for moving, evaporating and isolated droplets. A correction factor of the isolated droplet model, taking into account drop-drop interaction on the Sherwood and Nusselt numbers, is proposed.     

基于多组分蒸发模型的汽油机冷起动数值模拟

建立了汽油多组分油膜蒸发模型,并运用该模型对进气道喷射式汽油机冷起动首循环的气流运动、喷雾过程、油膜形成和发展过程、混合气形成过程及缸内燃烧进行了三维数值模拟,详细解析了油滴和油膜中每种组分的蒸发规律,给出了每种组分的浓度分布.模拟结果表明:冷起动时轻组分的蒸发主导首循环混合气的形成质量,中、重组分的蒸发情况仅起辅助作用;汽油的轻组分越多,燃料蒸发量越大,有利于形成稳定可靠的可燃混合气,改善缸内燃烧过程,提高起动稳定性;计算所得的缸压曲线与试验结果吻合良好,说明开发的多组分汽油蒸发模型具有较高的模拟精度.