【作者】 黄晨；

【导师】 尧命发；

【作者基本信息】 天津大学 ， 动力机械及工程， 2006， 硕士

【摘要】 均质压燃(HCCI)可实现内燃机高效、低污染燃烧,是满足未来更严格排放法规的重要燃烧新技术,近几年引起了国内外的高度关注。本文在发展了二甲基醚(DME)和二甲基醚/甲醇双燃料HCCI简化动力学模型的基础上,应用多维流体力学模型与简化动力学模型耦合计算,研究了二甲基醚单一燃料、二甲基醚/甲醇双燃料HCCI燃烧反应过程及有害排放物生成机理。计算结果表明,多维模型和零维模型对低温放热时刻预测基本一致;但对高温放热,由于多维模型考虑了缸内流动和缸壁传热,多维模型模拟结果比零维模型推迟,燃烧放热率峰值降低,与实测结果更为吻合。缸内温度变化历程分析表明,缸内温度随着燃烧的进行,从不均匀逐步发展到均匀,同时低温反应和高温反应并不是在燃烧室内部同时发生,而是在燃烧室局部先发生,然后发展到整个缸内;双燃料不仅改变DME反应途径,也改变了燃烧反应开始区域,DME单一燃料低温反应开始于活塞表面附近及压缩余隙区域,高温反应开始于燃烧室内较大的区域;双燃料准低温反应开始于燃烧室内较大的区域,高温反应开始于气缸轴线附近的核心区域,在双燃料中DME和甲醇几乎同时经历单阶段氧化过程。排放分析结果表明,HCCI主要的未燃碳氢排放是未燃燃料和甲醛(CH2O),而且未燃燃料占有很大比例,主要来源于残留在气缸侧隙中的燃料,这是HCCI燃烧效率低的主要原因;相对纯二甲基醚燃烧过程,双燃料未燃碳氢中未燃燃料占总未燃碳氢比例更大。DME燃烧过程中,未燃料燃料主要来源于侧隙的下部,CH2O排放主要生成于侧隙的中部,CO排放来源于气缸壁和侧隙上部;双燃料燃烧过程中,未燃燃料主要来源于气缸侧隙,CH2O排放主要生成于气缸壁附近,CO排放主要生成在活塞顶面,气缸侧隙内CH2O和CO生成量量很少。不同初始条件对HCCI排放生成影响研究结果表明,随着当量燃空比的减小,未燃碳氢和一氧化碳的排放上升,但当燃料浓度很小时,CO排放反而降低。双燃料中,随二甲基醚比例减小,未燃燃料和总碳氢排放增加,CO排放上升,但二甲基醚比例很小时,CO排放反而降低。更多还原

【Abstract】 Homogeneous Charge Combustion Ignition (HCCI) is a promising combustion mode that can achieve high efficiency and low emissions simultaneously, and it is also a key strategy to meet future emission regulations.A multi-dimensional model is adopted to investigate the combustion mechanisms and emission processes of Dimethyl Ether(DME) and Dimethyl Ether(DME)/Methanol(MEOH) dual fuel HCCI combustion processes. The multi-dimensional model couples the reduced chemistry and the CFD model.Simulation results indicate that low temperature reaction timing predicted by zero-dimensional model is the same as that predicted by multi-dimensional model. However, high temperature reaction timing predicted by multi-dimensional model is later than that predicted by zero-dimensional model, and rate of heat release is also lower, because the heat transfer and in-cylinder turbulence flow are considered in the multi-dimensional model. Cylinder temperature throughout the combustion process undergoes a process from inhomogeneity till homogeneity. Both low and high temperature reactions don’t occur simultaneously. Dual fuel not only changes the paths of DME reaction, but also the initial locations of combustion process. Low temperature reaction regions for DME HCCI combustion process are located near piston surface and squish region, and high temperature reaction occurs in the combustion chamber core zone. Quasi-low temperature reaction region for DME/MEOH HCCI combustion process resides in the combustion chamber core zone, and high temperature reaction is initiated in the combustion chamber core zone near the cylinder axis. DME and Methanol undergoes one stage oxidization process respectively. Emission analysis indicates that unburned fuel and CH2O account for the majority of unburned hydrocarbon (HC), and unburned fuel shares greater part. Much of unburned fuel resides in the piston-ring crevice region, which is the main reason of low thermal efficiency for dual fuel combustion process. Compared with pure DME HCCI combustion process, unburned fuel account for greater portion of HC for DME/MEOH HCCI combustion process. For DME HCCI combustion process, unburned fuel, CH2O and CO mainly resides in the bottom, middle and top of piston-ring crevice region respectively. For dual fueled HCCI combustion process, unburned fuel mainly resides in the piston-ring crevice region; the majority of CH2O is located next to更多还原