引射比对生物柴油斯特林发动机喷雾特性影响的仿真研究

基于斯特林发动机的喷雾特性,建立了某斯特林发动机旋流引射、喷雾的数学物理模型,模拟了高背压下生物柴油斯特林发动机在不同引射比下的喷雾过程。研究发现:生物柴油喷雾锥角随引射比的增大而增大,大引射比下的喷雾油束前端出现了明显的凹型回缩锋面;引射比越大,喷雾贯穿距越小;增大引射比,液滴速度增大,索特平均直径减小,粒径方差减小。高背压下,增大引射比能增大燃油混合气的空间分布,提高喷雾雾化效果。     

Influences of spray and operating parameters on penetration of vaporizing fuel droplets in a gas turbine combustor

The effects of inlet spray and operating parameters on penetration and vaporization histories of fuel droplets of a liquid fuel spray injected into a turbulent swirling flow of air through a typical can type gas turbine combustor, have been evaluated from numerical solutions of the conservation equations in gas and droplet phases. The computational scheme is based on the typical stochastic separated flow model of the gas-droplet flow within the combustor. A κ–ε model with wall function treatment for near wall region has been adopted for the solution of conservative equations in gas phase. The initial spray parameters are specified by a suitable PDF size distribution and a given spray cone angle. It has been recognized that the penetration of vaporizing droplets is reduced with an increase in inlet air swirl and spray cone angle. An increase in inlet air pressure or a decrease in inlet air temperature also results in a reduction in droplet penetration. The inlet air pressure and spray cone angle are found to be the most influencing parameters in this regard.     

涡流运动降低柴油机混合气浓度及碳烟排放的数值分析

为了揭示涡流运动对柴油机混合气形成及碳烟排放的影响规律，采用经过实验验证的喷雾及湍流模型，用CFD数值分析软件对某车用柴油机燃烧室内不同涡流条件下柴油喷雾的混合气浓度、速度矢量场、燃油液滴空间分布及油束特性进行了模拟计算．模拟结果表明，当涡流比从0到5．0依次增大时，过喷孔轴线的铅垂面内喷雾浓度场局部浓区燃空当量比逐渐降低，而过喷孔轴线且与铅垂面垂直的平面内喷雾浓度场局部浓区的燃空当量比则先降后升，而不是逐渐下降．只有合理选择剖切平面，即选择过喷孔轴线且与铅垂面垂直的平面，才能正确评价涡流运动对燃烧室内混合气浓度分布及碳烟形成区域分布的影响规律．组织燃烧室内气流运动，须兼顾与气缸轴线垂直的水平面内的涡流运动和过气缸轴线的铅垂面内的湍流或滚流运动．涡流比太大，铅垂面内的湍流或滚流太弱，会削弱喷雾射流对燃烧室底部空气的卷吸，降低燃烧室底部的空气利用率．随涡流比增大，射流顺涡流方向的弯曲度增大，不同喷孔的油束会发生相互干涉，在靠近气缸中心的区域内形成局部浓混合气，不利于降低碳烟排放．对具体的燃烧室结构和喷油系统，合理匹配涡流运动十分必要．     

涡旋式喷油嘴在柴油机上的应用

介绍了高压涡旋式喷油嘴的研究动态和应用现状,对涡旋式喷油嘴和直射式喷油嘴的雾化特性及其对内燃机燃油经济性和废气排放性能等方面的影响进行了对比分析,探讨了涡旋式喷油嘴在柴油机上应用的意义、可行性及所要做的工作。     

小型直喷式柴油机喷雾特性的试验研究

为了掌握喷雾的结构物特性,利用高速摄像装置和高压容器拍摄了喷雾的逆光图像,并研究了喷雾周围介质压力对喷雾贯穿距离、喷雾锥角以及蒸发等喷雾特性的影响。在液滴数密度较大的条件下,燃料液滴的蒸发速率传热过程和雾化质量的影响;喷射妆期喷雾的贯穿距离和贯穿速度几乎不受介质物影响;喷雾的贯穿跨离受喷油压力的影响不大,但随着喷油压力的提高,喷雾锥角增大,喷雾质量得到改善。     

双路离心式喷嘴雾化锥角的数值研究

利用Fluent软件,基于VOF（Volume—Of—Fluid）两相流模型对双路离心式喷嘴内的气液两相流动进行三维数值模拟。分别模拟喷嘴主油路单独供油、副油路单独供油与主副油路同时供油时雾化锥角,计算较好扑获了燃油在离心式喷嘴内所形成的空气涡及雾化锥角,所得喷嘴内压力分布、速度分布、相分布与雾化锥角,反映出该双路离心式喷嘴内流动特点,将计算结果与试验结果进行了对比分析。     

柴油和生物柴油喷雾特性的对比研究

为了研究生物柴油与柴油在雾化质量方面的差异,在燃油雾化质量评价理论的基础上,采用高速摄像机和马尔文激光粒度分析仪对柴油、生物柴油的喷雾特性进行了对比研究;计算分析了喷雾发展的不同时刻的喷雾锥角、贯穿距离,以及喷雾液滴的尺寸体积分布、累计体积分布、特征直径、平均直径和发散边界。结果表明:由于生物柴油的运动粘度、密度和表面张力都大于柴油,所以生物柴油的贯穿距、平均直径、特征直径、发散边界都比柴油的大,喷雾液滴的尺寸体积分布曲线和累计体积分布曲线都偏向大颗粒方向,喷雾锥角和相对尺寸范围比柴油的小,这说明生物柴油的雾化质量差。     

Vaporization and collision modeling of liquid fuel sprays in a co-axial fuel and air pre-mixer

Droplet collision occurs frequently in regions where the droplet number density is high. Even for Lean Premixed and Pre-vaporized (LPP) liquid sprays, the collision effects can be very high on the droplet size distributions, which will in turn affect the droplet vaporization process. Hence, in conjunction with vaporization modeling, collision modeling for such spray systems is also essential. The standard O’Rourke’s collision model, usually implemented in CFD codes, tends to generate unphysical numerical artifact when simulations are performed on Cartesian grid and the results are not grid independent. Thus, a new collision modeling approach based on no-time-counter method (NTC) proposed by Schmidt and Rutland is implemented to replace O’Rourke’s collision algorithm to solve a spray injection problem in a cylindrical coflow premixer. The so called “four-leaf clover” numerical artifacts are eliminated by the new collision algorithm and results from a diesel spray show very good grid independence. Next, the dispersion and vaporization processes for liquid fuel sprays are simulated in a coflow premixer. Two liquid fuels under investigation are jet-A and Rapeseed Methyl Esters (RME). Results show very good grid independence in terms of SMD distribution, droplet number distribution and fuel vapor mass flow rate. A baseline test is first established with a spray cone angle of 90° and injection velocity of 3 m/s and jet-A achieves much better vaporization performance than RME due to its higher vapor pressure. To improve the vaporization performance for both fuels, a series of simulations have been done at several different combinations of spray cone angle and injection velocity. At relatively low spray cone angle and injection velocity, the collision effect on the average droplet size and the vaporization performance are very high due to relatively high coalescence rate induced by droplet collisions. Thus, at higher spray cone angle and injection velocity, the results expectedly show improvement in fuel vaporization performance since smaller droplet has a higher vaporization rate. The vaporization performance and the level of homogeneity of fuel–air mixture can be significantly improved when the dispersion level is high, which can be achieved by increasing the spray cone angle and injection velocity.     

GDI发动机喷雾特性的数值模拟和试验

汽油直喷发动机高压燃油喷射系统与燃油经济性和废气排放等密切相关,通过试验和数值模拟对高压喷油系统和旋流喷油器的喷雾特性进行了研究.在不同喷射压力、背压压力条件下,利用高速摄像机对喷入定体积容器的喷雾进行了喷雾贯穿距离和喷雾锥角参数的测量.结果表明:在低背压压力下,喷雾呈现出空锥、较大范围的分布形态,有利于实现燃油与空气的均质混合;在高背压条件下,喷雾呈现出紧凑密集的分布形态,有利于实现燃油与空气的分层混合.获得的贯穿距离经验公式与试验测量值在一定范围内是一致的.基于AVL HYDSIM环境建立了一维高压喷油系统模型,模拟得到的针阀升程与试验获得的图像在时间上具有一致性.     

直喷式柴油机燃油撞壁特性及混合气形成研究

应用STAR-CD软件对燃油撞壁进行三维数值模拟,重点研究入射角度、环境压力和涡流比对撞壁特性和混合气形成的影响.结果表明,撞壁后燃油的二次雾化对燃油蒸发具有重要作用.随着壁面入射角度的增大,壁面油膜扩展面积增大,油膜从长叶形向扇形变化.随着环境压力的增高,燃油分布范围明显减小,但燃油堆积量和浓混合气的面积都会进一步减小,形成相对稀薄的混合气.涡流对燃油的影响主要发生在撞壁之后,随着涡流比的增大,形成大范围的稀混合气.涡流比过高,相邻油束的混合气将会发生干涉,造成燃烧质量下降.     

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。     

Direct measurement of entrainment during nanoparticle synthesis in spray flames

Using phase Doppler anemometry the scale of turbulence and the spray dilution by air entrainment are investigated during nanoparticle synthesis by flame spray pyrolysis (FSP). Ethanol and a solution of 0.5 M zirconium propoxide in ethanol are dispersed and combusted using an external-mixing, gas-assisted atomizer resulting in product ZrO₂ particles of about 11 nm in diameter as determined by nitrogen adsorption at a production rate of 100 g/h. Solution droplet size distributions of the solid cone spray are measured and related to standard correlations of spray atomization. Air entrainment and the radial spread of the expanding jet are determined from the gas velocities in horizontal planes across the spray cone at different heights above the nozzle. The isotropy of the turbulence is investigated using measured axial and radial velocity fluctuations. The turbulent flow is characterized by the integral time and Kolmogorov scales as well as the average shear rates acting on droplets and particles. The flow structure of these spray flames is of major importance as it determines product particle size, polydispersity, morphology, and crystallinity.     

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.     

Impingement of hollow cone spray on hot porous medium

To have a good understanding of the formation of homogenous mixture in a porous medium engine, the interaction between hollow cone spray and hot porous medium was studied numerically by using an improved version of KIVA-3V code. The improved KIVA-3V code is incorporated with an impingement model, heat transfer model and linearized instability sheet atomization (LISA) model to simulate the hollow cone spray. The reasonability of the impingement model and heat transfer model was validated. With a simple model to describe the structure of the porous medium, the interaction between hollow cone spray and hot porous medium was simulated under different ambient pressures and spray cone angles. Computational results show that the fuel spray could be divided into smaller ones, which provides conditions for the quick evaporation of fuel droplets and the mixing of fuel vapor with air. Differences in ambient pressure and spray cone angle affect the distribution of droplets in the porous medium.     

Effects of fuel droplet size on soot formation in spray flames formed in a laminar counterflow

The effects of fuel droplet size on soot formation in spray flames formed in a laminar counterflow are investigated experimentally and numerically. Sauter mean diameter (SMD) of quasi-monodispersed fuel spray (n-decane) is carefully controlled independently from the other spray characteristics using a frequency-tunable vibratory orifice atomizer, and the two-dimensional spatial distributions of soot volume fraction and soot particle size are measured by laser induced incandescence (LII) and time resolved LII (TIRE-LII), respectively. In addition, the soot formation processes are examined in detail by a two-dimensional direct numerical simulation (DNS) employing a kinetically based soot model with flamelet model. The results show that the soot formation area and location are strongly affected by the SMD of the fuel spray. As the SMD of the fuel spray increases, the average soot formation area expands, whereas local suppression of soot formation is instantaneously observed in the spray flames because of the appearance of groups of unburned droplets. The size of soot particles tend to be larger in the outer part of the soot formation area compared to soot in the inner part. This is because the surface growth of soot particles markedly proceeds compared to the coagulation and oxidation.     

掺混燃油在离心喷嘴内的流动与雾化特性研究

燃料性质的改变会导致雾化特性的变化,针对乙醇掺混航空煤油在离心式压力雾化喷嘴内的流动与雾化特性开展了研究。通过耦合流体体积法(VOF)和离散相模型(DPM),研究了不同乙醇掺混体积分数下掺混燃油在离心式喷嘴中的内部流动和外部雾化过程。研究结果表明：在压差不变时,喷嘴内空气芯直径随着掺混燃油内乙醇体积分数的增加而增大;而液膜厚度则与空气芯直径成反比,随着乙醇体积分数的增加而减小。喷嘴出口的速度随着乙醇体积分数的增加而增大;在油膜表面的波动及气动力的共同作用下,油膜失稳形成液滴,获得了不同比例下掺混燃油在喷雾外流场内的喷雾粒径分布特征,随着掺混乙醇体积分数的增加,液滴的平均直径逐渐减小。     

Experimental study on spray characteristics of ethanol-aviation kerosene blended fuel with a high-pressure common rail injection system

Partial replacement of fossil fuels by biomass based alternative fuels is considered as a possible option toward sustainability in aviation applications. The present work aims to study the changes in the spray characteristics in a pressure vessel when operated with aviation kerosene and ethanol-aviation kerosene blended fuel in a high-pressure common rail injection system. This research proposes the concept of adding a certain percentage of ethanol to aviation kerosene, creating ethanol-aviation kerosene blended fuel, which can decrease our reliance on fossil fuels on some level. The spray characteristics of the blended fuel, like spray tip penetration, spray cone angle and spray area, are studied in our work. Through the analysis, we can find that the atomization conditions have a significant impact on the spray characteristics of the aviation kerosene. Similarly, the experimental results show that the addition of ethanol has certain effect on the spray characteristics of the aviation kerosene. And the empirical equations applied in this study to predicting spray tip penetration and spray tip velocity provide a good agreement with the experimental data in the error-allowed range.     

考虑非定常效应的离心喷嘴初始雾化特征研究

为研究燃油流量瞬时变化时离心喷嘴的初始雾化特征,以高频激光和高速相机作为测试系统,以柱塞泵提供流量激励作为非定常输入进行了试验研究。研究表明：离心喷嘴初始雾化的初始液膜段流动稳定,基本无扰动;无流量激励下的液膜扰动段和初始雾化终点存在较明显的波动特征;在29.2%流量激励下的试验结果表明,流量激励不影响初始液膜的流动,但会导致初始雾化终点以1.8 mm的幅值和21 Hz的主频率呈周期性变化。     

Mechanistic study on spraying of blended biodiesel using phase Doppler anemometry

Droplet size and dynamics of blended palm oil-based fatty acid methyl ester (FAME) and diesel oil spray were mechanistically investigated using a phase Doppler anemometry. A two-fluid atomizer was applied for dispersing viscous blends of blended biodiesel oil with designated flow rates. It was experimentally found that the atomizer could generate a spray with large droplets with Sauter mean diameters of ca. 30 μm at low air injection pressure. Such large droplets traveled with a low velocity along their trajectory after emerging from the nozzle tip. The viscosity of blended biodiesel could significantly affect the atomizing process, resulting in the controlled droplet size distribution. Blended biodiesel with a certain fraction of palm oil-based FAME would be consistently atomized owing to its low viscosity. However, the viscosity could exert only a small effect on the droplet velocity profile with the air injection pressure higher than 0.2 MPa.     

螺旋形实心锥喷嘴雾化特性试验研究

为了对氨法脱硫用螺旋形实心锥喷嘴的雾化特性进行准确预测,基于高速阴影技术和图像处理方法,对两种不同螺旋升角的螺旋形实心锥喷嘴的流量特性、喷雾场结构特征、雾化角变化规律、破碎长度、液滴空间分布及平均粒径进行分析.结合脱硫常用的空心锥离心式喷嘴,开展了两种喷嘴的稳定性对比分析.结果表明:螺旋形实心锥喷嘴的流量特性与螺旋升角...