Simulation and Analysis on the Combustion Chamber of DI Diesel Engines with Spray-wall Impingement

为改善燃烧室内喷雾的空间分布,促进油气更好地混合,设计了一种新的直喷式柴油机撞壁喷雾燃烧室.对不同喷孔夹角在燃烧室内形成的近撞(包括全撞和半撞)及远撞喷雾方式的缸内混合气形成与燃烧过程进行了数值模拟.结果表明,从燃空比分布来看,半撞喷雾方式混合气最均匀,全撞方式次之,远撞方式最差.至于排放,远撞喷雾方式生成的NO排放最低,而半撞喷雾方式生成的碳烟排放最低.     

柴油机SCR系统车用尿素喷雾特性仿真与试验研究北大核心

通过建立喷射系统CFD三维仿真模型,研究了柴油机SCR系统在空气辅助雾化条件下尿素喷射的喷雾速度流场、雾化粒径、喷雾形态和贯穿距等变化规律,并通过试验对模型进行了验证;根据喷射模型对SCR系统的喷孔直径等结构参数进行了优化设计,通过发动机ESC,ETC试验对还原剂雾化性能进行试验验证。试验结果表明:采用改进后的柴油机空气辅助喷射还原剂供给系统后,柴油机NOx排放和NH3泄漏等指标均满足国Ⅴ阶段排放法规要求,验证了所采用的喷雾特性仿真优化设计方法有效可行。     

利用多孔喷油嘴改善燃油喷雾的雾化特性

研究的目的是改善直喷式柴油机喷油嘴的喷雾雾化特性,以获得较大的喷雾角,较短的液核长度,以及较小的液滴直径。在之前的研究中,已经利用单喷孔雾化增强喷油嘴,在相对较低的喷油压力下获得了良好的喷雾雾化特性。在研究中,调查了多喷孔雾化增强喷油嘴的相关特性,目的是改进并得到良好的雾化特性。分析了喷孔数、喷孔直径及喷孔位置等喷油嘴规格对喷雾雾化特性的影响。结果表明,相比单喷孔喷油嘴,利用4喷孔喷油嘴,可使分裂长度缩短约70%,喷雾角扩大约3倍,同时液滴直径极小,从而可获得良好的柴油喷雾雾化特性。     

斯太尔车为何冒白烟

故障现象 一辆斯太尔1491型(装配WD615.67柴油机)载货汽车,在运行中(已行驶120000km)发现柴油机动力不足、油耗增加、排气冒白烟的故障。 故障检查 拆下六个缸的喷油器进行压力和雾化检查,喷油压力正常,柴油喷雾良好。     

柴油机伞喷喷嘴内部流动的数值模拟

对柴油机伞喷喷雾及喷嘴内部流动的研究现状进行了分析,利用三维计算流体动力学(CFD)程序对喷嘴内气穴多相流计算模型进行了验证,在此基础上对柴油机伞喷喷嘴内部的流动特性进行了模拟计算分析。结果表明,在伞喷喷嘴喷孔进口处形成不对称的气穴,并逐渐延伸至出口处,从而对燃油雾化产生一定影响。     

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。     

超多喷孔喷射对高压共轨柴油机晚喷燃烧特性的影响

为实现柴油机的高效低排放燃烧,研究了在晚喷条件下的超多喷孔喷射对高压共轨柴油机喷雾、燃烧和排放特性的影响。利用KIVA-3V程序,对一台6缸高压共轨柴油机进行三维模拟,并对其进行了试验验证。结果表明:与传统喷油器相比,超多喷孔喷油器上、下层油束的干涉作用使喷雾形态显得分散很多,这有利于雾化和蒸发。采用超多喷孔喷油器后,呈预混燃烧。与传统喷油器方案相比,放热率峰值增大60%,NOx排放增大36%,碳烟生成区域明显减小、峰值下降48%。在保证动力性的前提下,采用超多喷孔喷油器和废气再循环技术、推迟喷油、提高喷射压力,NOx降低64%,碳烟降低46%。因而,这种柴油机能够实现高效清洁预混燃烧。     

柴油机多片碰撞喷雾的图像处理

进行了柴油机多片碰撞喷雾可视化的试验研究,并应用基于MATLAB工具箱而开发的数字图像处理程序对试验结果进行分析.结果表明,应用该程序可得到较清晰的喷雾二值图像,便于提取喷雾贯穿距、扩散角和扩散范围等信息,说明该程序是柴油机喷雾可视化研究的有效辅助手段.     

柴油机静态喷雾特性的实验研究

利用高速摄像装置和高压容器，拍摄了柴油机喷雾的逆光图像；研究了喷雾周围介质密度和种类对喷雾贯穿距离、喷雾锥角以及蒸发等喷雾特性的影响。     

Experimental study on macroscopic spray characteristics after impingement in a slit-type GDI injector

In this paper, an experimental study on the wall-impinging spray of the slit-type GDI injector is presented. To examine the effects of various factors on the development of a spray impinging on the wall, experiments were conducted at various injection pressures, ambient pressures, wall distances from the injector tip, wall temperatures, and wall inclination angles. Behavior of the impinging spray was visualized using a planar laser scattering method. It is shown that the spray path penetration of the wall-impinging spray increases with increases in injection pressure, wall distance, wall temperature, or wall angle. On the other hand, the spray path penetration of the wall-impinging spray decreases with increases in ambient pressure. The predicted spray path penetration calculated by the empirical equation estimates the spray path penetration in all cases, and the empirical equation is optimized for the total injection pressure.     

柴油机准均质混合气形成的数值模拟

利用KIVA-3V模拟了一台单缸二冲程柴油机通过早喷形成准均质混合气的过程,分析了喷嘴的不同结构对缸内混合气浓度场和温度场的影响。模拟计算表明,利用早喷可以形成稀薄准均质混合气;燃烧室形状影响混合气浓度场和温度场。为使稀薄准均质混合气在缸内合理分布,在不改变活塞ω形状的条件下,使用单孔喷嘴能有效避免燃油碰壁的发生。     

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。     

基于仿真分析的软岩隧道喷层厚度优化探讨

以西部某千枚岩软岩隧道为工程背景,采用三维有限元数值模拟手段对不同喷层厚度条件下围岩的洞周位移、喷层混凝土内力进行对比分析,对其随喷层厚度增加的变化规律进行研究。结果表明：喷射混凝土厚度的大小对软岩隧道围岩变形的控制作用不明显;喷层厚度的大小对下台阶开挖后的内力影响显著;喷射混凝土厚度对围岩变形控制具有一定作用,但仅限于一定厚度范围内,当喷层厚度超过一定量值后,喷层对于围岩变形控制效果将不再明显,但其对喷层内力的影响却更加显著。     

Study on unsteady gas jet and wall impingement jet — Comparison experimental results with numerical analysis by discrete vortex method

Generally speaking, it is very difficult to observe the growing process of large scaled vortices in a transient gas jet. The vortices have great effect on the mechanism of mixture formation between the jet itself and the surroundings. The objective of the study presented here is the clarification of this mechanism in both cases of a free jet and a jet impinging on a flat wall by means of the flow visualization of 21) image taken by thin sheet of laser light in the experiments and the numerical analysis by the discrete vortex method. The mechanism of the vortex growth and the coherent structure of vortices entraining the surroundings are observed in the case of the free jet. In the wall impinging jet, the structure inside the jet is divided into four regions, that is, free jet region, impingement region, wall jet region and wall jet vortex region. The results of the numerical analysis agree qualitatively well with the experimental data.     

喷雾夹角影响柴油机混合气形成与燃烧的CFD研究

运用CFD软件对直喷柴油机燃烧室中的喷雾及燃烧过程进行数值计算,考察了不同喷雾夹角下燃油的雾化过程、射流的发展形态以及近壁面区域浓度场的分布情况,并将计算结果进行了对比分析。结果表明,高速的射流漩涡对混合气的卷吸能力很强,油束末端的滞止区呈现较高的浓度;喷雾夹角过大会使燃油喷溅到燃烧室壁上,过小则活塞顶隙内的空气利用不充分,均对燃烧过程造成不良影响。     

锚杆施作时机对炭质千枚岩隧道力学响应影响研究

针对炭质千枚岩隧道施作锚杆时容易剥落掉块并导致局部失稳的问题,对先喷后锚法与传统先锚后喷法进行比较研究。为了分析2种施工方法对围岩与支护体系力学响应的影响,借助三维数值分析手段对洞周位移变化、初期支护结构受力、锚杆受力及围岩的塑性发展进行分析。结果表明,先喷后锚法引起的围岩变形与支护体系应力略大,先锚后喷法对控制围岩变形效果显著,二者均可满足一般工程需要;当对围岩变形控制要求严格时应选用先锚后喷法。     

Comparison of the Spray and the Spray/Wall Interaction of Two Gasoline Injectors

One important parameter influencing mixture formation and spray/wall interaction within engines is the geometry of the nozzle. In contrast to Diesel nozzles, the influence of the orifice geometry on spray formation has hardly be investigated for gasoline nozzles. In order to demonstrate the potential of adjusting the nozzle geometry of a modern GDI nozzle, we compare two six-hole, high-pressure nozzles with an identical structure, but different rounding radius of the orifice hole-inlet and different orifice hole-geometries: nozzle A with a rounded inlet and an orifice length to diameter ratio of 3/2 and nozzle B with a sharp inlet and an orifice length to diameter ratio of 1. In a first measurement campaign the spray formation is visualized using high-speed shadowgraphy imaging. The results show differences in spray angle and penetration depth. In a second measurement campaign we examine the spray/wall interaction and wall film formation by means of infrared thermography. The thermography measurements indicate that the geometry of nozzle B produces sprays with beneficial characteristics. This is very important for a clean combustion process and a decrease of soot emissions.     

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.     

基于可视化装置的柴油机喷雾燃烧过程试验研究

利用喷雾燃烧多功能动态可视化试验装置,获得了清晰直观的燃烧室内喷雾燃烧过程图片,分析研究了两种燃烧室对喷雾和燃烧过程的影响。结果表明:燃烧室内喷雾贯穿力比涡流和挤流强,喷雾以近似直线形式扩展到凹坑壁后,大部分随涡流方向扩展;火焰首先在靠缩口型燃烧室中心处出现,而圆柱型燃烧室则在靠凹坑上边缘处出现;缩口型燃烧室比圆柱型燃烧室燃烧结束得稍早,燃烧性能更好。