【作者】 张旭；

【导师】 刘会猛；

【作者基本信息】 华中科技大学 ， 动力机械及工程， 2015， 硕士

【摘要】 为了满足日益严苛的排放法规和燃油经济性要求,并减轻排气后处理器的负担,近年来,开发新的发动机燃烧技术以降低其自身排放的研究十分活跃,涌现出诸如均质压燃(HCCI)、汽油部分预混压燃(PPCI)和低温燃烧(LTC)等旨在实现发动机高效清洁燃烧的新型燃烧方式,它们有望解决内燃机PM排放和NOx排放Trade-off矛盾。但是,现阶段它们均面临着运行负荷范围偏小、着火时刻和燃烧速率难以控制、HC和CO排放高、冷启动和工况过渡困难等困境。由于这些燃烧方式的着火与燃烧由化学反应动力学所主导并在一定程度上受气流运动和油气混合控制,混合燃料这类燃料化学控制方法成为了解决这些困境的重要途径和手段。本文运用CFD数值模拟方法对汽柴油混合燃料喷雾特性进行了研究。首先,结合ECN喷雾实验数据库、依据经典线性稳定性理论对KH-RT破碎模型对环境条件的适应性进行了分析,指出提高喷雾破碎模型对不同环境条件适应性的方法和路径;然后,利用离散多组分蒸发模型对汽柴油混合燃料喷雾特性进行模拟,对比分析了单组份燃料和混合燃料在不同环境条件的喷雾贯穿距、SMD、燃油蒸发速率。仿真结果表明,混合燃料G50喷雾特性一般处在G0和G100之间,且G50各项喷雾特性参数与G0更为接近;环境温度对单燃料和混合燃料喷雾特性影响较大,主要表现在:随着环境温度升高,液滴的蒸发速率会大幅提升,特别是当环境温度高于液滴的临界温度时,液滴的蒸发速率可达90%以上。应用高速摄影和激光诱导炽光法(LII)对柴油喷雾燃烧过程进行可视化研究。在柴油喷雾燃烧过程中,可以观测到蓝色火焰、黄色或白色火焰,着火前期它以预混合燃烧为主,随时间推移火焰快速发展为扩散燃烧为主的燃烧方式。燃油喷射压力由100MPa减小到60MPa,柴油喷雾液相贯穿距略微减小,燃烧滞燃期变长;孔直径由0.15mm增大到0.25mm,柴油喷雾液相贯穿距增大,燃烧滞燃期变长。最后,利用详细化学反应动力学燃烧模型研究汽柴油混合燃料着火燃烧性能,随着汽油添加比例的增加,着火时刻不断延迟,火焰浮起长度增长。更多还原

【Abstract】 To meet the requirements of stringent vehicle emissions regulations and drastic reductions in fuel usage, new combustion concepts such as HCCI, PPCI and LTC have been studied widely. These new combustion modes have the potential to reduce the formation of particulate and NOx inside the cylinder simultaneously. However, these advanced combustion modes have suffered from uncontrollable ignition and combustion rates, narrow operating load ranges, high levels of CO and HC emissions, and difficulty in cold start and mode transitions. As one of the unique operating principles of these combustion modes is that the ignition and combustion are mainly dominated by the chemical kinetics of fuel/air/residual gas mixtures and are only moderately influenced by turbulence and mixing, fuel design and management strategy like blended fuel has become an important manner in which to resolve these difficulties and dilemmas.In this paper, the spray characteristics of gasoline–diesel blended fuel has been studied by CFD method. Firstly, a sensitivity analysis of classic KH-RT break-up model was made in different ambient conditions based on the Sandia laboratory experiment data on ECN website. Afterwards a discrete multiple-component evaporation model was used to compare the spray characteristics of single component fuel and blended fuel under different ambient conditions. Simulation results show that the spray characteristics of blended fuel G50, such as spray penetration, SMD and evaporation rate, are always in the middle of G0 and G100. Besides, increasing ambient temperature has a significant impact on the fuel spray characteristics, a higher ambient temperature causes to a faster fuel evaporation, especially when the ambient temperature is high above the droplet critical temperature, droplet evaporation rate increases dramatically to 90%.A visualization study of diesel spray & combustion processes have been done with the use of high speed photography and Laser-Induced Incandescence method. Blue flame, yellow flame and white flame can be observed during the combustion processes in chronological sequence, and premixed combustion developed to diffusion combustion. When injection pressure decreased from 100 MPa to 60 MPa, liquid penetration decreased slightly and ignition delay increased. What’s more, when injector hole diameter increased from 0.15 mm to 0.25 mm, liquid penetration increased from 35 mm to 55 mm and ignition delay increased. Finally, a reduced mechanism of PRF(Primary Reference Fuel) mechanism is incorporated in turbulent flame to simulate the chemical process of blended fuel. Simulation results show that with the increase of gasoline in blended fuel, the ignition delay period and flame lift-off length increase.更多还原