均质缸内直喷汽油机混合气形成过程的数值分析

针对某缸内直喷汽油机进行了喷油器喷嘴内部流场的多相流仿真分析,并将其结果作为初始条件输入到喷射模型中.将校定后喷射模型集成到缸内混合气动态分析模型,进而对发动机的缸内燃油与空气混合过程进行了欧拉--拉格朗日仿真分析.通过比较两款不同喷束的喷油器发现:缸内混合气的均匀度对于喷束布置较为敏感,比较宽广的喷束布置方案易于得到更加均匀的混合气.     

环境背压对多孔式喷油器雾化形态特征影响的数值解析

本文旨在通过数值模拟方法解析缸内直喷汽油机(GDI)多孔喷油器在不同环境背压条件下喷雾的形变特性及其影响机制。首先基于喷油器参数在Converge软件中建立了定容弹喷雾模型,进而根据高速摄影和相位多普勒粒子测试仪(PDPA)的试验结果对模型的喷雾宏观形态、贯穿距以及索特平均直径(SMD)进行了验证,在此基础上对0. 1,0. 5和1MPa环境背压条件下的喷雾形态变化进行了详细研究。研究结果表明:随着背压增加,油束被挤压并向喷油器中心轴线方向收缩,且贯穿距减小;由于油束对容弹内气流的冲击作用使得油束外边缘出现强烈的空气卷吸效应,致使在喷雾油束末端的液滴随气流向上回卷,且背压越高油束末端边界越不清晰;在喷雾压力场及速度场的分析中发现,由于喷雾内部区域压力低于外部,导致外部气流向内部冲击挤压油束,使得喷雾宽度减小,油束间相互作用增强,从而出现喷雾形变。     

缸内直喷汽油机多孔喷油器喷雾特性试验研究

为了研究缸内直喷汽油机多孔喷油器的喷雾特性,建立了定容喷雾试验装置,对不同环境压力和不同喷油压力条件下的自由喷雾和碰壁喷雾过程进行了拍摄,分析了壁面距离和壁面倾角对喷雾特性的影响。研究发现:多孔喷油器与传统的旋流式喷油器的喷雾特性存在较大差异。多孔喷油器的喷雾锥角受环境压力影响较小;随着环境背压的增大,贯穿距离和喷雾锥角呈现先增大后减小的特点;喷雾锥角随着喷射压力的提高略有增加。在碰壁喷雾发展过程中,不同环境压力下喷雾油束与壁面接触面积接近;随着壁面距离的增加,碰壁喷雾高度递减,碰壁后的喷雾高度存在波动;随着壁面倾角的增大,碰壁喷雾高度和增大。在壁面倾角的增大过程中,影响碰壁喷雾半径的因素较多,呈现出较复杂的变化规律。以上研究为多孔喷油器的设计及其与燃烧室的匹配提供了理论依据。     

采用空气辅助喷嘴的直喷发动机冷启动混合气形成CFD研究

直喷发动机缸内混合气形成过程的三维CFD分析对直喷燃烧室设计和喷油策略起到了重要作用。其中,喷油时刻对混合气分布的影响较大。经过对某四冲程活塞发动机的喷雾模拟,得到了较合适的喷油时刻。另外,文中采用了夹气喷油器,并与高压喷嘴进行了对比,结果显示采用夹气喷油器后,混合气准备较好。     

采用伸长结构的直喷汽油机喷油器的开发

对于汽车发动机降低排放和燃油耗的要求越来越高。在直喷汽油机方面必须解决一些技术课题,如缩短喷油器响应时期,提高燃油压力的耐受度和可变度,以实现最佳的燃油雾化及多次喷射。介绍了在喷嘴针阀的驱动部采用的伸长(拔长)结构的直喷汽油机用喷油器。它装备了新型电磁阀,并将转子与针阀设定为分体结构,同时利用转子的惯性提升针阀,能够适应喷油压力范围在3.5~20MPa,体积比传统喷油器缩小15%,质量减轻37%。     

缸内直喷汽油机的喷雾模拟

在定容弹内测量了某直列4缸均质缸内直喷汽油机不同时刻的喷雾油束形状和喷油器附近位置的喷雾液滴直径及速度分布,并在CFD模型中进行了喷雾的标定.分析了原机缸内喷雾、混合情况.研究了喷雾锥角、喷孔布置对缸内混合气均匀性的影响,论述了在低转速、部分负荷时加进气翻板的作用.结果表明,调整喷雾锥角、喷孔布置方式可以改善直喷汽油机缸内空燃比分布的均匀性;采用进气翻板可以提高发动机低转速部分负荷时缸内的滚流比及紊流强度,从而改善缸内混合气质量及加快缸内燃烧速度.     

MF-汽油掺混燃料直喷喷雾试验研究

电控直喷系统由于其具有良好的燃油经济性、热效率、排放和冷起动性能,广泛应用于SI发动机。目前2-甲基呋喃(MF)被证明是一种优于乙醇的生物质替代燃料,且其与汽油掺混燃料的直喷喷雾特性研究的较少。本文中应用6孔喷油器采用高速纹影技术研究M20,M40和汽油在不同环境背压和燃油温度下的喷雾特性。喷雾参数包括喷雾贯穿距、喷雾锥角和喷雾面积。结果表明,存在闪急沸腾和非闪急沸腾两种喷雾形态。当闪沸发生时,随着MF掺比的增加,喷雾贯穿距增加。随着环境背压的降低,贯穿距先减小后增加。喷雾锥角较未闪沸时增加,喷雾面积随着MF掺比的增加而增加并且与燃油温度呈负相关。当没有发生闪沸时,随着MF掺比的增加,喷雾贯穿距减小。     

喷雾燃油试验台定容弹设计

直喷汽油机的喷雾特性直接影响着缸内可燃混合气的形成和燃烧的过程,研究喷油器的喷雾特性对于提高发动机的燃油经济型和排放水平具有重要意义。喷雾定容测试系统是研究喷油器喷雾特性的主要手段之一。     

烟火式气体发生器燃烧室喷嘴的设计与研究

应用火药燃烧定律和喷嘴的流量速度公式可以计算和设计气体发生器燃烧室喷嘴的孔径和孔数。分别对气体发生器中不同燃烧室喷嘴尺寸进行引燃试验,可以看出,当计算出的燃烧室喷嘴的孔径和孔数为试验所采用时,该气体发生器燃烧室的压力与预先设定的数据基本吻合。此气体发生器产生的压力和时间能满足安全气囊的技术要求。     

基于缸内流动喷雾燃烧CFD仿真的直喷汽油机燃烧系统优化设计

对一款1.0L三缸增压直喷汽油机,建立了燃烧系统CFD仿真模型,并详细描述了换气、喷油器喷雾特性等边界条件的设置。分析了其额定功率点下的缸内瞬态流动、喷雾、混合气形成以及燃烧过程。原设计状态下,点火前缸内湍动能分布以及燃油浓度分布不够合理,火焰传播不对称,存在爆震风险。通过优化设计进气道及活塞冠面,缸内滚流运动及点火前湍动能提升,燃油浓度分布改善,燃烧速度加快约3°CA,同时由于omega涡流降低,排气侧湍动能改善,火焰均匀传播到气缸四周。最终的设计方案下,滚流、湍动能、火花塞周围流场、湿壁、燃油浓度分布以及火焰传播均能满足工程目标。在随后的单缸光学可视化发动机试验中,各工况下的混合气形成、湿壁及燃烧均能满足要求。     

Effects of injection parameters on the spray characteristics of swirl and slit injectors using the Mie-scattering method

We investigated the effects of injection parameters such as injection pressure, ambient pressure, and ambient temperature on spray characteristics. We calculated the turbulence occurring point (t _c ), defined as the time required to generate a vortex, and the deceleration point (t _b ), defined as the time when spray penetration begins to decelerate, to elucidate the breakup mechanism of the test injectors. The spray velocity coefficient (C_v) was obtained to evaluate the spray characteristics. As the ambient pressure increases in the case of a slit injector, C_v decreases. We investigated the effects of nozzle tip shape according to injection pressure, ambient pressure, and fuel properties on spray characteristics and provide a C_v value of 0.38 for the swirl injector with a spray angle of 60° and the slit injector under atmospheric conditions. The value of C_v in the case of a slit injector was reduced by increasing the ambient pressure. Our results suggest that C_v of a swirl injector is constant regardless of changes in ambient pressure, injection pressure, and fuel properties. On the other hand, C_v of a slit injector is altered by changes in ambient pressure.     

直喷汽油机中乙醇汽油宏观喷雾特性的试验研究

采用高速摄像技术在定容弹内对直喷汽油机多孔喷油器的喷雾特性进行了试验研究,以揭示喷油压力、环境压力对乙醇-汽油不同掺混比燃料的喷雾锥角、前锋面速度和喷雾投影面积的影响。结果表明,随着喷油压力的增大,喷雾锥角、前锋面速度和喷雾投影面积均增大;随着环境压力的增大,喷雾锥角增大,前锋面速度和喷雾投影面积减小。     

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.     

Effects of intake flow on the spray structure of a multi-hole injector in a DISI engine

The spray characteristics of a 6-hole injector were examined in a single cylinder optical direct injection spark ignition engine. The effects of injection timing, in-cylinder charge motion, fuel injection pressure, and coolant temperature were investigated using the 2-dimensional Mie scattering technique. It was confirmed that the in-cylinder charge motion played a major role in the fuel spray distribution during the induction stroke while injection timing had to be carefully considered at high injection pressures during the compression stroke to prevent spray impingement on the piston.     

2-甲基呋喃及其与异辛烷掺混燃料喷雾的微观特性研究

第二代生物燃料2-甲基呋喃(MF)由于其独特的物理化学性质受到学者们的广泛关注,研究MF以及它的掺混燃料在不同条件下的雾化效果也显得尤为重要。利用相位多普勒技术(PDPA),在不同喷射压力、环境温度、环境背压下,研究了MF、异辛烷以及两者等体积掺混燃料MF50喷雾的粒径与速度分布规律。结果表明:测试燃料的喷雾粒径整体分布呈现油束中心大,两端小的对称分布。微粒速度随环境背压的增加而降低,并且在低背压下速度为双峰分布,高背压下则是单峰分布。随着环境背压的增大,异辛烷粒径不断增加,MF粒径先减小再增加。     

Influence of nozzle hole diameter and orifice diameter on dme spray to get the similar heat value with diesel spray using the constant volume chamber

Low heating value (LHV) of di-methyl ether (DME) is lower than that of diesel. To get the similar heat value with diesel from the diesel engine operation, single injection quantity of DME should be increased. This investigation was tried to increase the injection quantity of DME by the modified diesel injector and investigated the penetration length and spray angle of DME spray. DME was injected by using three-type modified diesel injectors those nozzle-hole diameters (Injector 1: 1.66 mm, Injector 2 and 3: 0.25 mm) and orifice diameters were different (Injector 1 and 2: 0.6 mm, Injector 3: 1 mm). Spray characteristics of DME was investigated with a various ambient pressures (2.5, 5.0 MPa) in the constant volume chamber and a fuel was injected by varied injection pressure from 35 to 70 MPa by interval of 5 MPa using a DME common rail fuel injection system. The result shows that DME injection quantity by Injector 3 was 1.69 ~ 2.02 times larger than that of diesel injection quantity by Injector 1. In this case, DME spray got the similar heat value compared with diesel spray. The penetration speed of DME spray by Injector 3 was the fastest, thus when the spray development was end, the penetration length of DME spray by Injector 3 was the longest compared with the other cases. In case of the spray angle, Injector 2 and 3 had the similar spray angle and these were larger than that of diesel and DME sprays by Injector 1. As the result, Injector 3 was the solution for how to solve the low heating value of DME.     

柴油-甲缩醛混合燃料喷雾的粒子动态分析研究

为研究代用燃料甲缩醛的喷雾机理,采用基于相位多普勒原理的粒子动态分析仪(PDA),研究了不同百分比的柴油-甲缩醛混合燃料喷雾的粒度场、速度场。试验结果表明,柴油添加甲缩醛后,雾化得到改善,喷雾轴线上的粒子轴向速度提高,但三者径向速度相差不大。     

喷油器结构对柴油机性能影响的研究

着重介绍了对某大功率高速柴油机喷油器针阀体结构进行的改进研究,以改善喷油器的喷雾特性以及提高其流量,同时通过柴油机整机性能匹配试验,研究喷油器结构对柴油机整机性能的影响。