燃油近嘴区初始射流破碎及影响因素试验研究

搭建了燃油喷射雾化的可视化试验台架,采用数码相机和高放大倍数、高分辨率的长距离显微成像技术,以及纳秒级闪光灯作为相机曝光光源,对燃油近嘴区射流表面初始扰动微观结构进行可视化捕捉,结合图像后处理技术对射流表面结构参数和喷射参数进行定量测量和分析。研究发现,近嘴区初始射流表面波、液丝和液滴等产生、变形和破碎与喷油压力、空化以及环境背压密切相关。喷油压力增加,初始射流受到扰动增大,射流表面出现"坑洼"和"凸起"结构越靠近孔口;空化促进射流初始扰动、液丝和液滴的形成,致使喷雾锥角显著增加;环境背压增加,射流与环境介质之间剪切作用增大,可有效促进射流初始破碎,射流周围液丝进一步破碎形成液滴,有效地改善了雾化质量。     

燃油喷射雾化研究方法的现状及发展

本文就燃油喷射雾化的数值模拟计算和喷雾场测量两个方面，阐述了燃油喷射雾化研究的方法，介绍了冷冻法、摄影法、激光多普勒技术、激光全息法、激光阴影法等方法的原理、优点和不足，并指出了喷雾测试技术的发展前景。     

基于内窥镜的汽油发动机喷水可视化研究

设计了高速内窥镜系统,对汽油发动机进气道内的水雾喷射过程进行了可视化研究。对比了两种喷水器布置、不同喷水时刻和不同喷水压力下的水雾喷射过程,并结合台架数据分析了这些因素对发动机燃油消耗率和NO_x排放的影响。结果表明,在3 000 r/min@1.4 MPa工况下,使用3∶10的水油质量比,发动机喷水后燃油消耗率降低约3%,NO_x排放降低约20%。喷水器结构和布置方案对喷水效果影响不大。喷水时刻影响水雾进入缸内蒸发冷却的过程,不同喷水时刻下发动机燃油消耗率略有差异,NO_x排放变化趋势与燃油消耗率相反。喷水压力影响水滴雾化和运动过程,高喷射压力下雾化变好,但会使水滴在进气道内提前蒸发,反而降低其对缸内的冷却效果,试验在0.8 MPa喷射压力下燃油消耗率最低,而NO_x排放随着喷射压力的升高逐步降低。     

一种新的HCCI柴油机燃油喷雾特性的PLIF法测试装置

基于激光诱导荧光(PLIF)测试技术的原理，开发了一套可用于同时测量燃油气相和液相二维浓度场的测试系统，该测试系统包括高压燃油喷射系统、电路控制系统、氮气供给系统和可视化发动机。高压电控燃油喷射系统具有喷射压力高，且易于荧光剂的添加等优点，同时可以实现多脉冲燃油喷射。在光学发动机上进行了测试实验，研究了BUMP燃烧室内油束撞壁混合过程，观察了bump限流沿对于促进油气快速混合的现象。     

电控喷油器流量特性的仿真研究

研究了影响电控喷油器流量特性的因素,推导出初始喷油脉宽的计算公式.针对燃油喷射过程中出现的非线性动态不稳定流动情况,将喷射的燃油简化为油柱的变速运动,结合不同工况不同阶段燃油喷射速度特性与阀杆组件运动之间的关系,建立了能较精确预测流量特性与初始喷油脉宽关系的电控喷油器数学模型.基于该模型,对某一汽油发动机电控燃油喷射系统进行了仿真,结果表明模型正确有效.     

缸内直喷技术在小型汽油机上的应用研究

在1台单缸发动机上进行了汽油缸内直喷研究,设计了燃油供应系统、燃油电控喷射及台架测试系统。对部分台架试验结果进行研究分析,结果表明:改装的小型缸内直喷汽油机动力性能和排放性能均有明显改善;喷射时刻对排放有重要影响;在缸内直喷分层难以实现时,缸内直喷均质混合方式也是可行的研究开发方向。     

柴油机高压及微孔径下燃油雾化特性的数值研究(Ⅰ)——模型参数的选取

为了更精确模拟燃油雾化过程,探求适合超高压及微孔径下的燃油雾化模型,向计算流体力学平台KI-VA-3V中加入了大涡模拟程序及相应的雾化模型,数值研究了在超高压和微孔径条件下不同雾化参数对燃油雾化蒸发过程的影响.结果显示,破碎时间常数B1值对液相和蒸气相浓度有着重要影响,且对不同的湍流模型影响程度不同;随着B1的增加,喷...     

燃油喷射压力对缸内直喷汽油机喷雾特性的影响

燃油喷射压力对混合气形成有直接影响,提高喷射压力可进一步降低直喷汽油机微粒排放。使用STAR-CD软件分别建立定容弹和发动机缸内喷雾计算模型,利用喷雾特性可视化试验进行喷雾模型有效性验证,其后分析了燃油喷射压力对喷雾贯穿距、索特平均直径等基本特性参数的影响,研究了燃油喷射压力对缸内混合气形成的影响。结果表明提高燃油喷射压力可有效促进燃油的雾化蒸发,加快混合气形成,提高混合气分布均匀性。     

通用发动机SIDI缸内直喷技术解析

<正>缸内直喷就是将燃油喷嘴安装于气缸内,直接将燃油喷入气缸内与进气混合。喷射压的进一步提高,使燃油雾化更加细致,真正实现了精准地按比例控制喷油并与进气混合。通用燃油直喷技术的代号为SIDI,是Spark Ignition Direct Injection的缩写。一、SIDI燃油系统的组成如图1、图2所示,SIDI燃油系统由低压燃油系统和高压燃油系统2部分组成。低压燃油系统包括油     

柴油机均质混合气制备过程的数值模拟

针对复合式进排气系统燃油喷射混合新技术,对均质压燃(HCCI)柴油机的均质混合气制备过程进行了数值分析。建立了研究对象的物理模型和空气—燃油雾化混合的数学模型,对HCCI柴油机混合气形成过程特点与相关参数进行了详细的数值计算,并对复合式进排气系统内柴油喷雾蒸发和混合气形成过程以及影响因素进行了分析。数值研究表明,提出的复合进排气系统燃油喷射混合气制备技术能有效形成较均匀的预混合气,对进一步开发HCCI柴油机具有指导意义。     

转子发动机喷雾特性试验研究

利用定容弹、纹影仪以及高速相机等装置,就柴油转子发动机工况下的喷雾过程进行了试验研究,重点分析了喷雾环境背压和喷射压力对喷雾特性的影响。结果表明:在转子发动机喷雾过程中,喷雾扩散速度先快速增大后逐渐减小;喷雾锥角在初次雾化阶段内急剧减小,然后在二次雾化作用下保持相对稳定。喷雾环境背压的增大,有效减小了喷雾贯穿距离,增大了喷雾锥角,说明喷雾环境背压的增大对喷雾贯穿距离和锥角都有显著的影响,从而为转子发动机喷油正时的优化提供了试验数据支持;随着喷射压力提高,喷雾贯穿距离和喷雾锥角都增大,并且增大喷射压力加强了燃油的初次雾化和二次雾化,有利于提高转子发动机喷雾质量,为优化柴油转子发动机油气混合状态创造了条件。     

环境对大功率柴油机缸内喷雾、燃烧与传热的影响

采用准维多区数值仿真和环境模拟试验的方法,研究了不同海拔环境对某大功率柴油机缸内喷雾、燃烧和传热的影响。结果表明:在高原环境下,油核破裂滞后期比平原最大延长9.1°曲轴转角,油滴分裂长度增加29%以上,贯穿度明显增加,一次雾化后,SMD直径显著增加;海拔4 500m,瞬时放热率峰值降低18.4%,放热率重心后移近4°,最高燃烧压力降低18.8%,位置滞后0.6°;缸内对流换热和辐射换热都比平原明显增强。研究结果为探明特殊环境下柴油机性能劣化与故障机理提供了理论参考。     

Modeling on atomization and vaporization process in flash boiling spray

This paper presents the model analysis on atomization and vaporization processes in a flash boiling spray based on experimental results obtained from an injection system in the suction manifold of a gasoline engine. Two kinds of liquid fuel, n-Pentane and n-Hexane, are injected into quiescent gaseous atmosphere at room-temperature with low pressure through a pintle type injector. Fuel spray is observed, by taking photographs, with variation of the ambient back pressure. Then, in the flash boiling spray region where the back pressure was below the saturated vapor pressure of fuel, the bubble nucleation process due to flash boiling was modeled by both experimental results and the nucleation rate equation as a parameter of the pressure difference between back pressure and vapor pressure. Further, the fuel vaporization process was assessed by considering growth calculation of cavitation bubbles and fuel evaporation from the film surface due to heat transfer at the gas-liquid interface. Accordingly, we could estimate quantitatively the transient changes in the bubble growth and the vapor mass fraction inside the spray for each back pressure condition.     

柴油机射流碎裂的影响因素

液体射流雾化质量对改善内燃机缸内的燃烧过程非常重要,因此柴油喷雾射流碎裂影响因素的研究在内燃机领域中具有重要的使用价值和学术意义。液膜碎裂的影响因素除了自身的物理因素(如粘度、表面张力、雷诺数)外,还有一些其他因素,如液体射流的温度、射流速度和喷孔几何形状等,因此研究液体碎裂过程应全面考虑这些因素对它的影响。     

Numerical modeling of hollow-cone fuel atomization,vaporization and wall impingement processes under high ambient temperatures

In the following paper, a numerical study of the atomization, vaporization and wall impingement processes of hollow-cone fuel spray from high-pressure swirl injectors under various ambient temperature conditions was carried out. Also, the availability of applied models and the effect of ambient temperature on spray characteristics is discussed. The Linearized Instability Sheet Atomization (LISA) model combined with the Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model, the improved Abramzon model and the Gosman model are used to calculate the atomization, vaporization and wall impingement processes of hollow-cone fuel spray, respectively. Spray models are implemented with the modified KIVA code. The calculation results of the spray characteristics under two ambient temperatures, including spray tip penetration, spray structure and radial distance after spray-wall impingement are compared to the experimental results obtained by the Laser Induced Exciplex Fluorescence (LIEF) technique. The droplet size distribution, ambient gas velocity field, vapor phase distribution and fuel film mass generated by spray-wall impingement, measurements which are generally difficult to obtain by experimental methods, are also calculated and discussed. Quantitative discussions on the effect of the ambient temperature on the spray development process are conducted. It is shown that the applied models are applicable even in the high ambient temperature condition.     

Experimental investigation of characteristics of pressure modulation in a fuel injection system

A piezoelectric atomization device achieves fuel pressure modulation through vibration of a piezoelectric pressure modulator. As a consequence, the fast alternating and slow moving streams collide with each other and further break up the fuel drop. In this paper, an experimental investigation was carried out to study the fluid dynamic characteristics of the spray atomization process of automotive port fuel injectors with a piezoelectric pressure modulator. The investigation mainly focuses on: (a) the coupling characteristics between the piezoelectric stack and the hydraulic as well as the transfer characteristics of pressure modulation from the piezoelectric modulator to the point above the orifice; (b) the time history of the pressure dynamic response at the point above the orifice under a typical modulation frequency, which reflects the variation of pressure modulation while the fuel injector is working; and (c) the time-variation characteristics related to mechanical structure and fluid dynamics. The experimental results expose some important dynamic characteristics of pressure modulation, which will be very significant and lead us to greatly improve the fuel injection system, optimize the control parameters and implement spray atomization with a high quality performance in the near future.     

Modeling of gasoline fuel spray penetration in SIDI engines

The paper presents a research on the fuel injection and atomization depending on the thermodynamic quantities inside the cylinder of a combustion engine. With the use of piezoelectric outward-opening injectors the changes in the geometrical quantities of the atomized fuel in the aspect of its injection were determined. The studies concerning the influence of the individual quantities on the fuel spray penetration injected by the outward-opening injectors comprise a synthesis of the injection and atomization tests. Own mathematical equation describing the fuel spray penetration was proposed. The exponents (equation coefficients) related to the influence of the fuel pressure, air backpressure, charge density and time of fuel spray development were determined with the coefficient of determination 0.9797, indicating a congruence of the experimental data with the values obtained on the basis of the mathematical equation.     

喷嘴孔数及其布置对汽油直喷喷嘴闪沸喷雾-环境气体相互作用影响的研究

为了区分火花塞点火式缸内直喷(SIDI)发动机喷雾和环境气体两相流场,将优化后的高速双色PIV(Particle Image Velocimetry)技术应用于多孔直喷喷油器的喷雾和环境气体速度的测试.此双色PIV系统由一个特殊的示踪和滤波系统组成,可同时对燃油喷雾及其环境气体的速度场进行测量.本研究采用该双色PIV方法研究不同环境压力和燃油温度的条件下,喷嘴孔数及其布置情况对燃油喷雾和环境气体的相互作用的影响.在此研究中,对3个汽油直喷喷嘴做了详细的研究,包括1个6孔喷嘴,1个3孔喷嘴及1个2孔喷嘴.研究结果表明,随着燃油温度的提高或者环境气体压力的降低,喷雾雾化增强,燃油颗粒粒径减小,导致喷雾油束变宽,喷雾与环境气体接触面积变大,喷雾和环境气体的两相流场的作用变强.不同孔数和布置的喷油器在冷态及闪沸条件下油束间干扰作用的强度不同,导致喷雾传递给环境气体的动能不同.较强的油束间的干扰作用加强了燃油喷雾与环境气体之间的动量交换过程,进而增强了环境气体的动能.     

Analysis of the transient atomization characteristics of diesel spray using time-resolved PDPA data

The transient atomization characteristics of a single-hole diesel spray were investigated to clarify the time-dependent droplet formation process of the spray through time-resolved analysis of the droplet size data acquired by using a 2-D PDPA (phase Doppler particle analyzer). Comparisons among the three single-hole diesel nozzles on the atomization characteristics were made to confirm the effects of the hole-diameter. The hole diameter of the single-hole diesel nozzles varied with d_n=0.22, 0.32 and 0.42 mm. The time-resolved diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) of droplets in diesel spray injected into still ambient air were measured. The SMD and AMD decreased with decreasing nozzle hole diameter. The SMD distribution along the spray centerline steeply decreased with increasing axial distance before reaching a constant value. In the time-dependent analysis of the SMD of the whole flow field, the SMD gradually increased with time after the initiation of injection, reached a maximum value, and then decreased.     

Effect of the number of fuel injector holes on characteristics of combustion and emissions in a diesel engine

The diesel combustion process is highly dependent on fuel injection parameters, and understanding fuel spray development is essential for proper control of the process. One of the critical factors for controlling the rate of mixing of fuel and air is the number of injector holes in a diesel engine. This study was intended to explore the behavior of the formation of spray mixtures, combustion, and emissions as a function of the number of injector hole changes; from this work, we propose an optimal number of holes for superior emissions and engine performance in diesel engine applications. The results show that increasing the number of holes significantly influences evaporation, atomization, and combustion. However, when the number of holes exceeds a certain threshold, there is an adverse effect on combustion and emissions due to a lack of the air entrainment required for the achievement of a stoichiometric mixture.