【作者】 潘锁柱；

【导师】 宋崇林；

【作者基本信息】 天津大学 ， 动力机械及工程， 2012， 博士

【摘要】 随着机动车排放法规的日益严格，缸内直喷(GDI)汽油机颗粒物排放已成为近年来关注的热点。论文针对GDI汽油机颗粒物排放的相关基础问题，开展了数量、粒径分布、微观结构及颗粒相多环芳香烃（PAHs）排放等物理化学特性的研究，并考察了燃烧组织措施对其影响规律；同时，采用数值模拟方法进行了颗粒物形成历程及空燃比对其影响规律的初步探索。本文研究工作将进一步揭示GDI汽油机颗粒物本质，为采取有效措施降低其排放提供理论依据。具体研究成果如下：1. GDI汽油机排气颗粒物除怠速工况外，均呈包括核态和积聚态的双峰分布，其中核态数量较多，积聚态数量较少；与气道喷射（PFI）汽油机相比，其质量浓度、表面积浓度以及积聚态数量在多数工况下均较高。此外，其颗粒物排放与燃烧组织措施之间存在密切的相关性。采用稀混合气和推迟点火定时均可显著降低颗粒物数量，合理优化喷油定时和采用EGR技术均可降低积聚态颗粒物数量。2. GDI汽油机排气颗粒物主要由准球形基本碳粒子团聚而成，呈不规则几何形状，组成元素主要是碳（C）、氧（O）元素，另外还含有多种金属和非金属元素，且具有典型的自相似分形特性，分形维数介于1.36-2.38之间。燃烧组织措施对颗粒物分形维数影响较大，采用计量比混合气和推迟点火定时均会导致其增大，加入EGR则会使其减小。3.基本碳粒子主要为洋葱状微晶碳结构，及少量无序和无定形结构。其粒径分布类似高斯分布，峰值在20-35nm，微晶尺寸呈单峰分布，峰值在0.4~0.6nm，70%以上小于1nm，层间距分布在0.28~0.58nm，70%以上在0.34-0.44nm，曲率在1~2之间，峰值在1.2~1.6。此外，基本碳粒子微观结构参数与燃烧组织措施密切相关。采用计量比混合气、提前点火定时和喷油定时以及加入EGR均会使粒径增大；采用浓或稀混合气、推迟点火定时和喷油定时以及加入EGR均会使层间距增加；采用计量比混合气、推迟点火定时、提前喷油定时和加入EGR均会使曲率增大。4.采用电子能量损失谱（EELS）考察了燃烧组织措施对GDI汽油机颗粒物石墨化程度的影响规律。结果发现，采用计量比混合气、推迟点火定时、提前喷油定时以及加入EGR均会降低颗粒物石墨化程度，导致其氧化活性增加。5．颗粒相的PAHs排放规律研究表明，4环结构PAHs排放量最高，其次是5环结构PAHs，两者之和占总PAHs排放量58.70%以上，2环结构PAHs排放量最少，不到总PAHs排放量的7.50%。采用稀混合气、提前喷油时刻和减小EGR均可降低总PAHs排放量。6.采用AVL-Fire软件，建立了碳烟模型。模拟结果表明，碳烟在火焰传播过程中经历了生成与氧化的过程，其形成与燃空当量比以及燃烧温度密切相关。更多还原

【Abstract】 With the increasingly strict requirements for vehicle emission regulations, theparticulate emission from gasoline direct injection (GDI) engine has been receivedconsiderable attention in recent years. In this dissertation, series of investigations havebeen performed to shed light on the physicochemical characteristics of particulateemission from GDI engine, including particle number, particle size distribution,microstructure and particle-phase polycyclic aromatic hydrocarbons (PAHs), and theeffect of combustion control parameters on them. Meanwhile, the three-dimensionalnumerical simulation has been adopted to explore preliminarily the formationhistories of particulates and the effect of air/fuel ratio. These research works willfurther reveal the essence of particulates from GDI engine, and provide theoreticalbasis for adopting effective measures to reduce particulate emission. The majorcontributions are listed as follow:1. Except for idle operation condition, exhaust particulates from GDI engine are ofbimodal distribution consisting of nucleation mode and accumulation mode particle,where the particle number with nucleation mode is more than that with accumulationmode. The mass concentration, surface area concentration and the amount ofaccumulation mode particles from GDI engine are generally higher as compared tothose from PFI engine in most operation condition. Furthermore, there is closerelationship between the particulate emission from GDI engine and the combustioncontrol parameters. The total particle number is obviously decreased with adoptinglean air/fuel mixture or delaying spark timing, and the number of accumulation modeparticle is decreased with reasonably optimizing injection time or adopting exhaustgas recirculation (EGR) technology.2. The exhaust particulates from GDI engine are fractal-like agglomeratesconsisting of quasi-sphere primary particles, which mainly compose of carbon (C),oxygen (O) element, and many kinds of trace metal and nonmetal elements. Theseparticles possess typical self-similarity fractal character, and the fractal dimension isin the range of1.36~2.38. Moreover, combustion control parameters have greatinfluence on the fractal dimension, which will increase with using stoichiometricair/fuel mixture or delaying spark timing, and decrease with introducing EGR intocylinder.3. Besides a small amount of disordered and amorphous structure, onion-shellcrystallitic carbon structure is found to be dominant in primary particles. The sizedistribution of primary particles is similar to Gauss distribution with the peak value of particle diameter in the range of20~35nm. Fringe length of primary particles shows aunimodal distribution with the maximum value in the range of0.4~0.6nm, and70%of that is less than1nm. Fringe separation of primary particles is in the range of0.28~0.58nm, with more than70%of that locating in0.34~0.44nm. Tortuosity ofprimary particles spreads from1to2with peak value in the ranger of1.2~1.6.The microstructure of primary particle is closely related to combustion controlparameter. Adopting stoichiometric air/fuel mixture, advancing spark timing andinjection timing and introducing EGR will cause the growth of primary particle.Fringe separation obviously increases while employing lean or rich air/fuel mixtures,delaying spark timing and injection timing and introducing EGR. Meanwhile,Adopting stoichiometric air/fuel mixture, delaying spark timing, advancing injectiontiming and introducing EGR will bring about bigger bending of primary particlemicrocrystal.4. An electron energy loss spectroscopy was employed to estimate the effect ofcombustion control parameter on the graphitization degree of exhaust particulates.The results indicate that adopting stoichiometric air/fuel mixture, delaying sparktiming, advancing injection timing and introducing EGR will decline thegraphitization degree, resulting in an enhanced oxidation activity of particles.5. Particle-phase PAHs were investigated, and the results show that the emissions offour-ring PAHs is highest, followed by five-ring PAHs, and the subtotal emissions ofboth account for more than58.70%of total PAHs. The lowest emissions of PAHs aretwo-ring PAHs, which account for less than7.5%of total PAHs. Furthermore,Adopting lean air/fuel mixture, advancing injection timing or reducing EGR will leadto a decrease in total PAHs emissions.6. A numerical simulation model for soot particles of GDI engine was establishedby AVL-Fire software. The results show that the soot simultaneously undergoes theformation and oxidation process during the flame propagation, and its formation isclosely related to fuel/air equivalent ratio and combustion temperature.更多还原