【作者】 郭红松；

【导师】 苏万华；

【作者基本信息】 天津大学 ， 动力机械及工程， 2010， 博士

【摘要】 对于柴油机而言,燃油的喷射、雾化及其与空气的混合是整个燃烧过程的一个关键环节,然而前人对柴油喷雾的研究主要是在较低环境密度(35kg/m3以下)下开展的,距离现代重型柴油机高负荷工况(环境密度达60 kg/m3以上)相差很远,有必要对现代重型柴油机相似环境条件下柴油喷雾场进行深入定量研究。本文设计、开发了定容燃烧弹系统,实现了最高1100K温度和60kg/m3密度的喷雾环境模拟,对气、液相柴油喷雾温度场和浓度场进行了定量标定。在此基础上,本文使用复合激光诱导荧光技术在定容燃烧弹内定量研究了环境温度、环境密度、喷油压力、喷孔直径、氧气浓度等对重型柴油机相似环境条件下柴油喷雾结构和浓度场的影响。研究中,环境温度为800-1100K,环境密度为20-100kg/m3,喷油压力为100-220MPa,喷孔直径为0.10-0.18mm。研究发现,现代重型柴油机相似环境条件下柴油喷雾结构可以使用气液相喷雾锥角、贯穿距离,液核区,气相喷雾外壳,气相喷雾浓混区(Φ>2)、稀混区(Φ≤2),气相喷雾头部等参数来描述,据此本文还建立了重型柴油机相似环境条件下柴油喷雾结构模型,该结构模型中液核区域同时存在当量比相对较高的气相喷雾,这和John Dec建立的喷雾模型是不同的。现代重型柴油机相似环境条件下,气液相喷雾浓度由外到内从0逐渐增大到最大值,气相喷雾温度由外到内从环境气体平均值逐渐下降到最低。喷雾发展过程大致可以分为初期、中期、充分发展期三个阶段,在喷雾发展初期,液核长度随时间基本呈线性增长,气液相喷雾贯穿距离和锥角基本一样,气相喷雾当量比较小;在喷雾发展中期,液核长度随时间成抛物线性增长直至液核达到其最大长度,气液相贯穿距离仍然基本一致,气相喷雾瞬态最大当量比不断增大;在喷雾充分发展期,液核长度基本不变,气相喷雾继续向前发展,其瞬态最大当量比达到最大值并开始下降,液核、气相喷雾浓混区、气相喷雾低温核区基本重叠。研究还发现,重型柴油机相似环境条件下,环境密度、环境温度、喷孔直径、喷油压力和氧气浓度等对柴油喷雾动态结构和浓度场具有重要影响,对着火时刻柴油喷雾结构和浓度场(Φ-T图上燃烧路线始点位置)也有着重要影响。在增加充分发展期气相喷雾头部稀混区气相燃油比例,改善其均匀性,增厚气相喷雾外壳方面,减小喷孔直径、降低环境温度和提高环境密度具有很强的可替代性,同时减小喷孔直径、降低环境温度还可使气相喷雾最大当量比大幅下降。重型柴油机相似环境条件下,降低环境温度接近800K着火时刻气相喷雾不存在浓混区。更多还原

【Abstract】 For diesel engine, fuel injection, atomization and mixing with the air is a key step to the whole combustion process. However, the study of diesel spray were mainly carried out in the low ambient density (below 35 kg/m3) by predecessor by far, which is far from the modern heavy-duty diesel engine high-load operating conditions (ambient density of 60 kg/m3 and above). It is necessary to quantitatively study the diesel spray under the modern heavy-duty diesel engine similar conditions.A constant-volume bomb was developed to obtain high ambient density and high temperature environment. The highest 1100K temperature and density of 60kg/m3 environmental simulation was achieved. The concentration and temperature both of vapor phase and liquid phase were quantitatively calibrated. On this basis, the effects of ambient density, ambient temperature, injection pressure, injector diameter and oxygen concentration on diesel spray structure and concentration were quantitatively studied under heavy-duty diesel engine similar conditions in the constant-volume bomb by using planar laser induced fluorescence technique. The experimental range of temperature was 800-1100K and 20-100 kg/m3 for density, and 100-220MPa for injection pressure, and 0-10-0.18mm for injector diameter.It was found that the diesel spray structure could be described by parameters such as penetrations and cone angles both of vapor phase and liquid phase, liquid core, the sheath of vapor phase spray, dense mixed zone (Φ> 2), lean mixed zone (Φ≤2), vapor phase spray head and so on under heavy-duty diesel engine similar conditions. Accordingly, structure model of diesel spray was established under heavy-duty diesel engine similar conditions, in which there was vapor phase spray with relatively high equivalence ratio in the liquid core zone, which is different from the spray model established by John E. Dec. The concentration both of vapor phase and liquid phase gradually increase from 0 to a maximum from outside to the inner, the temperature of vapor phase spray decreases gradually from the mean environmental value to the lowest from outside to the inner under heavy-duty diesel engine similar conditions. Spray development process can be divided into three stages of early, mid, full development period. In the early stage of spray development, liquid core length increases linearly with time, the penetrations and cone angles both of vapor phase and liquid phase are almost the same with each other, the equivalence ratio of vapor phase spray is low. In the middle stage of spray development, liquid core length increases exponentially with time until to its maximum value, the penetrations and cone angles both of vapor phase and liquid phase are almost the same with each other too, the transient maximum equivalence ratio of vapor phase spray gradually increases. In the full development stage of spray, liquid core length remains basically unchanged, vapor phase spray keeps on developing forward, there is obviously vapor phase spray head, the transient maximum equivalence ratio of vapor phase spray rises to its maximum value and then decreases, liquid core、vapor phase dense mixed zone and vapor phase low temperature core overlap each other in principle.It was also found that the ambient density, ambient temperature, injection pressure, injector diameter and oxygen concentration had important influence on the diesel spray temporal structure and concentration, the diesel spray structure and concentration near ignition timing (namely the starting point of combustion path in theΦ-T diagram) were significantly impacted by the factors too under heavy-duty diesel engine similar conditions. For the increase of vapor phase fuel mass fraction in the lean mixed zone and improvement of spray homogeneity in the vapor phase spray head, and incrassation of the sheath of vapor phase spray, the reduction of injector diameter and decrease of ambient temperature and increase of ambient density were highly substitutable. Moreover, the maximum equivalence ratio of vapor phase spray significantly decreased by the reduction of injector diameter and decrease of ambient temperature. There was no dense mixed zone in the vapor phase spray when ambient temperature was reduced to 800K near ignition timing.更多还原