横向气流中喷雾粒径的变化规律

以液体为燃料采用连续方式工作的某些动力设备,如某些燃气轮机、液体火箭发动机等,液体燃料经由喷嘴喷射进入横向气流中.与静止空气中的雾化过程相比,横向气流作用使雾化粒径发生变化,喷雾粒径与横向气流速度及喷嘴安装角密切相关,运行和设计这类燃烧设备时都需要对此加以考虑.通过试验和数值计算对横向气流中喷雾粒径及其变化规律进行了研究,结果表明,喷雾粒径数值计算与试验结果间吻合较好,但在喷雾雾滴与横向气流间相对速度相差较大区域,计算与试验结果一致性变差.     

喷孔夹角对直喷汽油机混合气形成与燃烧特性的影响

基于试验验证了喷雾模型和燃烧模型,采用CFD技术研究了喷孔夹角对直喷汽油机喷雾发展、混合气形成以及缸内燃烧特性的影响.研究结果表明,增加喷孔夹角,减小喷雾之间相互作用,有利于燃油雾化,改善了缸内混合气及缸内燃烧,提高了缸内压力和放热率.喷孔夹角大小的选择直接影响直喷汽油机缸内混合气质量与燃烧优劣.     

簇孔式喷油嘴喷雾雾化特性的研究进展

燃油喷雾雾化特性直接影响燃烧,从而也极大地影响了柴油机的各项性能,而喷嘴在很大程度上决定了燃油的喷雾雾化特性。本文基于现有研究文献,介绍了簇孔式喷油嘴的概念及其喷雾雾化特性,通过与传统单孔喷嘴的比较实验,阐述了簇孔式喷嘴的在喷雾贯穿距离,喷雾锥角,雾化能力等喷雾特性上的独特优势。这一新型喷嘴的提出与应用,对改善喷雾雾化与燃烧,提高发动机性能具有重大意义。     

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。     

同轴气流式液体射流雾化机理研究进展

同轴气流式液体射流雾化广泛存在工业燃烧领域中,研究液体射流雾化机理对于提高燃烧效率,降低污染物排放有十分重要的意义。从雾化理论、初次雾化形态、二次雾化形态三方面综述了同轴气流式液体射流雾化研究现状及发展,对圆柱射流、平面射流和环形射流的线性稳定性理论研究、气流作用下的形态变化、划分模式和影响因素进行了系统地阐述,分析了液滴破碎形态和理论的研究现状。最后总结了气流作用下液体射流雾化的影响因素和研究发展方向。     

柴油机多片碰撞喷雾的雾化及燃烧特性

基于搭建的喷雾可视化系统对两种方案的多片碰撞喷雾进行了可视化研究.试验中分别使用普通柴油及掺有一定比例乙醇-汽油的柴油,对碰撞方案和乙醇汽油的加入对于柴油机排放的影响进行了试验.结果显示,与多片全碰喷雾方案相比,多片半碰喷雾具有更好的雾化及排放特性.混合适当比例乙醇-汽油的柴油具有更快的燃烧速度以及更短的燃烧持续期.与...     

静电喷雾高压喷射下喷雾特性的研究

静电喷雾技术通过液体荷电来改善液体雾化质量，该技术有望在较低压力下获得与高压喷射相当甚至更优的雾化质量，或与高压喷射相结合获得更好的雾化质量以进一步改善内燃机性能。将静电喷雾技术在泵一管～嘴喷射系统上进行了实验，对高压喷射下柴油的静电喷雾瞬态喷雾特性进行了研究。荷电后可观察到静电喷雾分层喷雾的特征，喷雾中后期扭曲并且湍流增强，喷雾径向宽度增大，后喷液柱消失；荷电后喷雾前端粒径的均匀度得到改善。     

伞状喷雾及HL喷雾在柴油机均质预混合燃烧中的应用研究

针对柴油机均质预混合燃烧的混合气形成提出满足喷雾碰壁少，雾化好等要求的早期喷射缸内预混合方式，并对喷雾状态、性质及其预混合燃烧做了深入探讨。对HL喷雾与多孔喷雾做了比较研究。试验证明，HL喷雾具备双工作模式的能力。     

汽油喷雾撞壁雾化的数值模拟

撞壁雾化是现代直喷式中小缸径发动机中普遍存在的现象,研究撞壁雾化的特性对改善发动机的燃烧具有重要的意义。根据Mundo等人提出的飞溅喷雾撞壁模型,对定容室中的汽油喷雾撞壁现象进行了模拟计算与分析。通过改变壁面温度、壁面粗糙度、喷雾速度及网格数,对比分析了不同条件下喷雾撞壁过程发生的变化,为进一步进行喷雾撞壁试验、完善喷雾撞壁模型提供了参考。     

喷雾雾化式液体型汽车加热器燃烧室的设计

本文主要针对喷雾雾化式液体型汽车加热器对于燃烧的特殊要求,探讨对其燃烧室的设计与计算.     

Dynamics and stability of lean-premixed swirl-stabilized combustion

Combustion instability remains a critical issue limiting the development of low-emission, lean-premixed (LPM) gas turbine combustion systems. The present work provides a comprehensive review of the advances made over the past two decades in this area. Recent developments in industrial dry-low-emission (DLE) swirl-stabilized combustors are first summarized. Various swirl injector configurations and related flow characteristics, including vortex breakdown, precessing vortex core, large-scale coherent structures, and liquid fuel atomization and spray formation, are discussed. Nonlinear behaviors of combustion processes observed in combustors are described. The influence of fuel preparation, combustor geometry, and operating conditions on combustion characteristics in swirl-stabilized combustors is examined. The mechanisms driving combustion instabilities, including hydrodynamic instabilities, equivalence ratio fluctuations, flame surface variations, and oscillatory liquid fuel atomization and evaporation are investigated. Instability stabilization methods, including both passive and active control techniques, are also reviewed. Finally, recent progress in both analytical modeling and numerical simulation of swirl-stabilized combustion are surveyed.     

液态燃料跨/超临界喷射研究进展

对国内外近年关于液态燃料跨/超临界喷射的实验及数值模拟研究进行综述和分析。分析表明:超临界作为一种不可规避的工况,其喷射具有完全不同于亚临界喷射的特性,气液界面消失,液滴和液丝等结构由高密度流体团代替,成为一个由湍流支配的无相变的扩散过程。现有研究多是对跨/超临界喷射现象的观测与描述,对该现象产生的机理及其对燃烧的影响尚不明确。采用传统喷雾模型进行超临界喷射仿真,得到的结果与实验现象有很大误差;采用真实流体状态方程所进行的仿真可大幅减小这个误差,但结果仍不理想。指出:跨/超临界喷射对燃烧稳定性的影响是航空航天领域的研究方向,而内燃机领域则更关注跨/超临界喷射对短暂雾化过程以及燃烧效率的影响。     

不同喷油压力RP-3航空煤油、柴油碰壁喷雾着火和燃烧特性的对比研究

利用直径0.22mm的单孔喷嘴高压共轨喷油器,以喷油器油量标定数据及控制参数为基础,采用高速相机成像技术在定容燃烧室内在等喷油量变喷油压力的前提下测量了着火点、着火滞燃期、燃烧持续期、火焰面积(AF)和火焰自然发光强度(SINL)的变化规律,对比研究了RP-3航空煤油、柴油碰壁喷雾的着火和燃烧特性。结果表明:在低喷油压力下着火点分布在离壁面较远的区域,在较高喷油压力下着火点位于壁面上,距喷油器中心线的距离随喷油压力的增加而增加,且RP-3航空煤油着火点距喷油器的距离比柴油更远。随着喷油压力的增加,RP-3航空煤油碰壁喷雾火焰的着火滞燃期先降低后增加,柴油碰壁喷雾火焰的着火滞燃期不断降低,且RP-3航空煤油具有更短的着火滞燃期。燃烧持续期随喷油压力的增加而降低,RP-3航空煤油的燃烧持续期比柴油短。喷油压力越高,火焰面积(AF)和自然发光强度(SINL)的变化速率越高,而AF和SINL的最大值及达到最大值所需的时间越小。与柴油相比,RP-3航空煤油的AF、SINL具有更高的变化速率,且AF、SINL的峰值更高,达到峰值的时间更短。     

柴油机燃油喷射雾化的PIV测量试验研究

介绍了先进的粒子图像测速技术(PIV)应用于燃油喷雾过程的试验研究结果，燃油通过多种孔径的单孔和多孔喷油嘴喷入一个定容压力室内，采用高分辨率的CCD摄像机记录整个喷射过程，可以观察到喷雾场内部结构．结果分析显示，高速射流表面存在不稳定扰动波，在气动力作用下，液滴发生分裂破碎，呈现枝状分离表面．瞬态速度矢量图显示，气液界面处存在大尺度的卷吸涡流运动，有助于油气扩散混合。     

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。     

Break-up characteristics of gelled propellant simulants with various gelling agent contents

Gel propulsion systems have many advantages with respect to high performance, the energy management of liquid propulsion systems, storability, high density impulse, and low leakage of liquid propellants. The atomization process provides sufficient contact surface area between the gelled fuel and oxidizer jets. It is important to study how injection characteristics of gelled propellants are related with break-up and spray distribution. The break-up and mixing processes are very important in achieving maximum efficiency and necessitate the careful study of combustion instability. Gelled propellants are non-Newtonian fluids in which the viscosity is a function of the shear rate, and they have a high dynamic shear viscosity which depends on the amount of gelling agent contents. The present study has focused on the break-up process, wave development of ligament and liquid sheets formed by impinging jets with various gelling agent contents. Especially, the break-up processes of the impinging jets at the initial conditions are studied. The break-up process of like-on-like doublet impinging jets are experimentally characterized using non-Newtonian liquids which are mixed by ionized water 98.5 wt%, Carbopol 941 0.5wt% or 1.0wt%, and NaOH（concentration 10%） 1.0wt%. For the like-on-like doublet injector, the generation of a liquid sheet at the impinging point of two jets was observed. The spray shape with elliptical pattern is distributed in a perpendicular direction to the momentum vectors of the jets. Gelled propellant simulants with high viscosity jets are more stable and produce less pronounced surface waves than low viscosity jets. Generally, the break-up length decreased due to the increasing Reynolds number. However, surface waves and atomized droplets increased. Gelled propellant simulants from like-on-like doublet impinging jets have the spray shape of closed rim patterns at low pressure. Also, the rim patterns of spray have no disturbances on the spray sheet. As the injection pressure increased, rimless patterns which were composed of ligament sheets and small droplets emerged due to the effect of the aerodynamic action. Periodic wave-like structures observed from the near impingement point and atomized droplets were observed at a location further downstream.     

Mixing characteristics of pulsed air-assist liquid jet into an internal subsonic cross-flow

Penetration depth,spray dispersion angle,droplet sizes in breakup processes and atomization processes are very important parameters in combustor of air-breathing engine.These processes will enhance air/fuel mixing inside the combustor.Experimental results from the pulsed air-assist liquid jet injected into a cross-flow are investigated.And experiments were conducted to a range of cross-flow velocities from 42～136 m/s.Air is injected with 0～300kPa,with air-assist pulsation frequency of 0～20Hz.Pulsation frequency was modulated by solenoid valve.Phase Doppler Particle Analyzer(PDPA) was utilized to quantitatively measuring droplet characteristics.High-speed CCD camera was used to obtain injected spray structure.Pulsed air-assist liquid jet will offer rapid mixing and good liquid jet penetration.Air-assist makes a very fine droplet which generated mist-like spray.Pulsed air-assist liquid jet will introduce additional supplementary turbulent mixing and control of penetration depth into a cross-flow field.The results show that pulsation frequency has an effect on penetration,transverse velocities and droplet sizes.The experimental data generated in these studies are used for a development of active control strategies to optimize the liquid jet penetration in subsonic cross-flow conditions and predict combustion low frequency instability.     

直喷式柴油机气缸内喷雾贯穿及分布的研究

本文建立了燃油喷过程及气缸内喷雾特性的统一计算模型。考虑了燃油喷射、气缸内空气运动和燃烧室结构对喷雾贯穿及分布的影响。     

Spray and combustion characterization for internal combustion engines using optical measuring techniques - A review

The number of studies on spray and combustion characteristics in IC (internal combustion) engines using optical techniques has rapidly increased in the past few years due to an increase in the number of alternative fuels and stricter emission standard regulations. This study investigates better ways of controlling the combustion process, thus ensuring optimum performance and minimum emission levels produced during the combustion process. Alternative fuels such as CNG (compressed natural gas), biodiesel and hydrogen have been studied by many researchers due to their relative low environmental impact. Meanwhile, for conventional fuels such as gasoline and diesel, studies have focused on spray characteristics to provide better air/fuel mixtures in order to produce a cleaner combustion process. Few experimental works have investigated the effects of modifications to the injector itself, for example, varying the injection rate, injection pressure, etc. In order to provide a better understanding of spray and combustion characteristics, researchers have studied macroscopic and microscopic parameters using optical techniques. This paper presents the significance of spray and combustion study with optical techniques that have been reported by previous researchers in order to provide in depth knowledge as assistance to readers interested in this research area.