空气雾化喷嘴的设计与实验研究

为提高喷嘴雾化效率,基于维多辛斯曲线理论对喷嘴出口结构进行优化,研制出一种新型渐缩式空气雾化喷嘴,并搭建了喷雾实验平台进行实验。利用图像处理技术对实验数据进行分析,提取不同结构喷嘴的喷雾粒径和雾化锥角分布,通过对比仿真和试验结果分析喷嘴气液夹角对雾化效果的影响。研究表明:喷嘴喷雾实验和仿真结果较吻合,相对误差在6.5%以内;喷嘴气液夹角α=20°时,雾化锥角最大,液滴索特尔平均直径最小,雾化效果最好。     

汽油机缸内直喷喷嘴结构参数对雾化特性的影响研究

为了改进缸内直喷汽油机用电磁涡旋式喷嘴的喷雾特性,对喷嘴孔径、螺线管电阻和涡旋片等结构参数进行了优化设计,并在喷雾试验台上对燃油质量流量、喷雾发展过程、喷雾锥角、喷雾贯穿距、针阀延迟和喷雾粒径分布进行了试验验证。结果表明:优化设计后的喷嘴的质量流率大于原商用喷嘴的质量流率,而质量流率的线性度接近原商用喷嘴。在相同喷射时间5ms及喷油压力9.5MPa下,当喷嘴孔径由0.55mm增大为0.70mm时,喷雾发展过程较为快速,燃油流量增加约56%,喷雾锥角增加10°,但喷雾不稳定性也随之提高,雾化粒径增大。不同喷油压力下的喷雾锥角变化较大,靠近喷嘴的喷雾轮廓与孔口设计有关。喷油压力增大时,其质量流率会随之增大,雾化粒径分布在10μm～20μm范围内的喷雾液滴体积分数也会随之上升,从而提高雾化程度。     

不同压力下燃油溶气量的研究

燃油溶气喷雾燃烧对同时降低柴油机的氮氧化合物和碳烟微粒有明显效果,为了了解不同压力下燃油的溶气量,对不同压力下二氧化碳分别溶入C14H28和柴油的量进行了测试研究。试验表明：燃油溶气量主要取决于气体的性质、燃油的物性、溶气压力和溶气时的环境温度,随着溶气压力的提高,柴油和C14H28溶入的二氧化碳量呈上升趋势。     

DPF主动再生柴油喷雾氧化的试验及模拟研究

综合可视化试验和数值模拟手段,研究分析了柴油机颗粒捕集器(DPF)主动再生时柴油氧化催化器(DOC)上游柴油喷雾特性及柴油在DOC内的氧化过程。利用高速摄影装置拍摄了柴油喷雾图像,分析了喷雾贯穿距和喷雾锥角,并利用相位多普勒粒子分析仪(PDPA)对喷雾粒径进行了测量。标定了DOC内的柴油氧化模型和喷雾模型,在此基础上对柴油喷雾及燃油在DOC内的氧化过程进行了模拟。试验结果表明:柴油喷射速率越高,喷雾贯穿距和喷雾锥角越大;喷射速率对喷嘴出口处喷雾粒径分布有较大影响,沿喷雾轴线方向液滴的索特平均直径(SMD)随大粒径液滴数的变化而变化。模拟结果表明:柴油喷雾特性决定了排气管路和DOC入口处的碳氢(HC)分布;DOC出口处温度分布与DOC入口处HC分布具有密切的对应关系;碰壁及重力作用使得HC向排气管路底部集中,HC质量浓度接近2%;管路底部柴油过浓使得DOC出口截面底部的对应区域温度较低,低于450℃;增加排气管路长度可促进喷雾与气体的混合均匀性,缓解管路底部的柴油过度集中现象。     

燃油喷嘴气液两相流雾化特性研究

以空气,水为工质,利用马尔文粒度分析仪对气液两相流雾化器喷嘴的雾化特性进行了详细的实验研究。测量了气,液两相流不同入口压力比条件下通过喷嘴后形成的液体雾化粒子的粒径分布,详细讨论分析了气,液两相压力及进气,进液方式对喷雾效果的影响,得出了喷嘴雾化过程中气液两相流量与气液两相压力之间的规律和 化原则,并对喷嘴的雾化机理进行了探讨。     

横向流速度对旋流式喷嘴雾化影响的数值分析

为了研究横向流速度对旋流式喷嘴雾化的影响,通过对旋流式喷嘴在横向流场中的雾化场进行数值模拟;模拟结果给出了喷雾流场随横向流速度变化的规律,并得到了不同横向流速度下喷雾液滴的索特平均直径（SMD）,进一步分析了喷嘴出口下游截面雾化粒径的分布情况。     

Y型喷嘴性能的数值分析

利用F luen t软件模拟气流式雾化喷嘴的喷雾,计算了不同的入口条件下,喷嘴喷雾的液体雾化粒径;讨论了不同的液体和气体压力以及它们的比值对喷雾效果的影响;模拟结果与实验数值吻合很好。分析结果表明,液体压力的增大不利于雾化,而随着气体压力的增大雾化效果改善显著,但是气液压力比满足一定的匹配数值才能保证良好的雾化效果。     

喷嘴结构对喷雾特性的影响

为了解高压共轨喷嘴结构对喷雾的影响,试验采用三维相位多普勒粒子分析仪(PDPA),在高喷射压力条件下研究了不同的喷嘴结构的喷雾粒径空间分布情况.结果表明:高压燃油喷雾的粒径分布呈现轴线大、两边小的趋势,并在喷雾边缘稍微增加;同时随着喷射压力的增加,喷雾索特平均直径(SMD)的分布呈现粒径减小的趋势,小粒径区域逐渐向喷嘴顶端靠近,喷雾雾化效果随喷射压力增加而改善.随着喷孔直径的减小,喷雾总体SMD呈减小趋势;当喷孔直径减小到一定程度时,进一步减小喷孔直径对喷雾雾化效果的影响逐渐减弱.孔径为0.18,mm的喷嘴,喷雾SMD随着长径比(L/D为3.89~5.00)的增加而增大;孔径为0.13,mm的喷嘴,喷雾SMD随着长径比(L/D为5.38~7.69)的增加而降低.     

LPG溶入柴油的喷射雾化特性研究

在燃油溶气雾化原理的基础上，利用数码照相机拍摄了LPG溶入柴油的喷雾空间形态，计算和分析了喷雾液滴的平均直径、尺寸分布以及液滴尺寸累积体积分布的特征直径和发散度。结果表明，LPG混入柴油，喷雾角增大，油粒细小均匀，燃料的雾化质量明显改善，在较低的喷射压力下可以获得理想的雾化效果，从而改善柴油机的烟度排放。     

定容弹中船机相似工况下燃油雾化特性的数值研究

确定了柴油喷雾参数,确保该参数下模拟贯穿距与试验数据吻合较好;然后基于验证的喷雾模型,研究了不同喷油角度时涡流对喷雾形态、贯穿距、燃油蒸发质量和液滴平均粒径(SMD)的影响,以及不同燃油温度和环境温度在涡流作用下对柴油喷雾贯穿距、蒸发质量和液滴平均粒径(SMD)的影响;最终得出优化喷雾特性的策略。结果表明:涡流方向与喷雾方向相反或垂直时,涡流作用可以抑制喷雾轴向贯穿距发展;涡流与喷雾相切时,涡流可以促进喷雾轴向贯穿。涡流能够增强液滴与环境气体的相互作用,增加燃油蒸发质量,降低液滴平均直径。在涡流作用下不同燃油温度和环境温度对燃油贯穿距影响不大,提高两者可以使蒸发质量增加,两者对液滴平均直径的作用不同:燃油温度提高,喷油过程中SMD的峰值增加,最终SMD变化不大;环境温度提高,SMD的峰值和最终值都下降。当400K燃油以涡流切向喷射到温度为900K的环境气体中时,能够实现最优的雾化特性。     

溶有甲烷柴油稳态喷雾特性的试验研究

对溶有甲烷柴油的稳态喷雾特性进行研究。喷雾特性和形状分别由激光粒度分析仪LDSA1300A和数码照相机记录。试验使用了六个不同长径比L／D的直圆孔喷嘴。溶解压力和喷射压力范围分别是0．1MPa到10MPa和5MPa到10MPa。研究了甲烷溶解度、测量位置、喷射压力和喷嘴参数对喷雾特性的影响。结果表明：在柴油中溶入甲烷,出现了减压沸腾喷射现象;与纯柴油相比,喷雾形状和锥角产生了很大变化;流量系数随着溶解度和L／D值的增加而减小;甲烷溶解度和L／D的共同作用对雾化有正反两方面的影响。     

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.     

燃料设计改善发动机燃烧和排放的研究(1)--燃料参数设计与喷雾特性研究

研究了通过含氧燃料与柴油相互掺混来改变燃料的成分与输运参数、改善燃料的喷雾特性，从而降低了柴油机的排放。选择了几种典型的含氧燃料一乙醇、碳酸二甲脂(DMC)、甲缩醛(DMM)，测量和分析了它们以不同比例与柴油互溶后燃料的输运参数变化。为了考察混合燃料的喷雾特性，以不同比例的DMM柴油混合燃料为例，运用激光相位多谱勒(PDA)技术测量它们的索特平均直径(SMD)，并与柴油进行了比较。研究结果表明：通过含氧燃料与柴油的互溶互混，重新设计了燃料的输运参数和成分后，显著改善了燃料的喷射雾化特性。     

Impact of alternative fuel properties on fuel spray behavior and atomization

In order to verify and solve the problem of NOx and PM emissions, it is necessary to directly observe the internal combustion chamber of a diesel engine. Many studies have been performed in recent years to verify the macroscopic and microscopic behavior of the injected fuel spray because observing it is not easy due to the difficulties of the experiment. Researchers have investigated the spray characteristics for various diesel injector nozzles over a wide range of temperatures and pressure, but there is lack of evaluation for the spray characteristics for biodiesel. At a time when rapid rise of fuel prices and depleting hydrocarbon resources of the world have forced us to look for alternative fuels biodiesel produced by transesterification of non-edible vegetable oils is promising to be an important additive/substitute to petro diesel. Biodiesel being an oxygenated and sulfur-free fuel leads to more complete combustion and lower emissions. But, the energy content or net calorific value of biodiesel is less than that of diesel fuel; also it has higher viscosity and density, than diesel fuel. A considerable improvement in these properties can be obtained by mixing diesel and biodiesel and then using the blends. Biodiesel and biodiesel/petro diesel blends, with their higher lubricity levels, are increasingly being utilized as an alternative. Present paper analyzed the correlation of injection parameters that will affect the spray characteristics of biodiesel. Observations for analyzing the effect of injection parameters on spray cone angle, break up length and fuel penetration were made. Finally the performance and emissions tests were studied. Atomization and vaporization of fuel are greatly influenced by viscosity and density of fuel and these properties are temperature dependent. Thus fuel inlet temperature plays a very important role in fuel atomization process. At higher temperature viscosity of fuel decreases which enhances the atomization of biofuels.     

柴油中溶入甲烷对发动机燃烧排放特性的影响

设计了几种不同甲烷含量的甲烷／柴油混合燃料,在实用柴油机上对它们的燃烧和排放特性进行了试验研究。研究结果表明,根据柴油中甲烷含量的不同,溶气对比油耗和热效率有正反两方面的影响;溶有甲烷的柴油与纯柴油相比有较长的着火滞燃期和较低的最大放热率;柴油中甲烷的溶解量越大,滞燃期越长,最高放热率越低;与纯柴油相比,溶有甲烷柴油的NOx排放降低,HC排放增加;在较高的甲烷溶解度时,NOx和烟度排放能够同时降低。     

Experimental investigation concerning the influence of fuel type and properties on the injection and atomization of liquid biofuels in an optical combustion chamber

Due to the scarcity of fossil fuels and the future stringent emission limits, there is an increasing interest for the use of renewable biofuels in compression ignition engines. However, these fuels have different physical, chemical and thermodynamic properties affecting atomization, spray development and combustion processes. The results reported in this paper have been obtained by experimentation with a constant volume combustion chamber. The influences of physical fuel properties on injections under non-evaporating conditions are studied, using a pump-line-nozzle system from a medium speed diesel engine with injection pressures up to 1200 bar, by changing the fuel type and temperature. Experiments were conducted for diesel, biodiesel, straight vegetable oils and animal fats. Injection pressure and needle lift measurements were analyzed. A high speed camera was used to visualize the spray, which enabled us to study the spray penetration and spray angle. Our results show that the fuel temperature is an important parameter to control because it significantly affects the fuel properties. Both the injection timing and injection duration are affected by the fuel properties. The influences of these properties on the spray development were less pronounced. At low temperatures, a strongly deteriorated atomization of oils and fats was observed.     

Spray characteristics and controlling mechanism of fuel containing CO2

This paper presents studies of spray characteristics and controlling mechanism of fuel containing CO₂. Using diesel fuel containing CO₂ gas, experiments were conducted on diesel hole-type nozzles and simple nozzles. The steady spray and transient spray characteristics were observed and measured by instantaneous shadowgraphy, high-speed photography, phase Doppler anemometry (PDA) and LDSA respectively. The effects of CO₂ concentration in the fuel, the injection pressure, the nozzle L/D ratio, surrounding gas pressure and temperature on the atomization behavior and spray pattern were evaluated. The results show that the injection of fuel containing CO₂ can greatly improve the atomization and produce a parabolic-shaped spray; and the CO₂ gas concentration, surrounding gas pressure, temperature and nozzle configuration have dominant influences on spray characteristics of the fuel containing CO₂. New insight into the controlling mechanism of atomization of the fuel containing CO₂ was provided.     

Combustion performance and emission reduction characteristics of automotive DME engine system

This article is a condensed overview of a dimethyl ether (DME) fuel application for a compression ignition diesel engine. In this review article, the spray, atomization, combustion and exhaust emissions characteristics from a DME-fueled engine are described, as well as the fundamental fuel properties including the vapor pressure, kinematic viscosity, cetane number, and the bulk modulus. DME fuel exists as gas phase at atmospheric state and it must be pressurized to supply the liquid DME to fuel injection system. In addition, DME-fueled engine needs the modification of fuel supply and injection system because the low viscosity of DME caused the leakage. Different fuel properties such as low density, viscosity and higher vapor pressure compared to diesel fuel induced the shorter spray tip penetration, wider cone angle, and smaller droplet size than diesel fuel. The ignition of DME fuel in combustion chamber starts in advance compared to diesel or biodiesel fueled compression ignition engine due to higher cetane number than diesel and biodiesel fuels. In addition, DME combustion is soot-free since it has no carbon–carbon bonds, and has lower HC and CO emissions than that of diesel combustion. The NO_x emission from DME-fueled combustion can be reduced by the application of EGR (exhaust gas recirculation). This article also describes various technologies to reduce NO_x emission from DME-fueled engines, such as the multiple injection strategy and premixed combustion. Finally, the development trends of DME-fueled vehicle are described with various experimental results and discussion for fuel properties, spray atomization characteristics, combustion performance, and exhaust emissions characteristics of DME fuel.     

闪急沸腾喷雾速度场的LDA研究

为探索代用燃料液化石油气LPG和二甲醚DME的喷雾机理,采用LDA技术测量了喷雾粒子的速度分布。为安全起见,用制冷剂R12作试验液体,它与LPG和DME有相似的物理特性。为做比较,在相同试验条件下对传统柴油喷雾进行了测量。考察了喷雾模式对速度分布的影响。结果表明,R12喷雾的速度分布比传统柴油喷雾均匀得多,前者的平均径向速度远大于后者。这被认为归因于闪急沸腾大大改善了雾化和液气混合。