【作者】 张博；

【导师】 郑朝蕾；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2013， 硕士

【摘要】 近些年来，生物柴油作为一种新型的环保型柴油机替代混合物受到各国的青睐，它的物化特性与柴油类似，可以直接作为现有的柴油机燃料，同时排放性能又优于传统的发动机燃料。因此，生物柴油在减少石油消耗和保护环境两方面都具有重要意义。本文首先是以葵酸甲酯(C₁₁H₂₂O₂)和正庚烷（nC7H16）作为生物柴油替代混合物，构建一个包含有691种组分，3226个基元反应的生物柴油替代混合物的详细化学动力学机理。其次在不同工况的激波管条件下验证了该详细机理的着火延迟时间是合理的。然后通过HCCI发动机条件下缸内燃烧计算其缸内压力以及不同工况下主要排放物等证明该构建机理是合理的，可用来计算内燃机燃烧过程的数值模拟。通过对生物柴油替代混合物在HCCI发动机条件下燃烧过程的分析，发现生物柴油替代混合物的燃烧过程呈现低温燃烧阶段和高温燃烧阶段两阶段放热过程，且这两阶段的放热过程被负温度系数区域（900¹000K）隔开；同时还可以知道，正庚烷在低温阶段主要是通过脱氢自由基OH、HO2等的脱氢作用以及加氧过程消耗掉，而葵酸甲酯除通过脱氢作用和加氧作用消耗外，还可以通过分解反应生成含碳原子数更少的甲酯基，这主要是由于其脱氢产物葵酸甲酯基内部结构的化学键能的不平衡造成的。通过对燃烧过程中N元素的演变历程的分析可知，进入汽缸中的N2到NO_X的变化过程中，自由基CH₃、OH、H、O和O2为其重要的中间物质，通过控制这些重要中间物质的生成可以有效的减少废气中NO_X的排放。利用敏感性分析法和路径分析法相结合的办法，对前期构建的生物柴油替代混合物进行机理简化，得到了一个包含有113种物质和306个基元反应的简化动力学模型。通过与不同条件下激波管实验条下以及详细机理着火延迟时间的对比发现，该简化机理能够很好地吻合正庚烷和葵酸甲酯的着火延迟时间；通过对不同工况下HCCI发动机燃烧条件下，生物柴油简化机理与实验机理的对比分析发现，该简化机理能够很好的吻合缸内的压力和缸内的温度，同时能够很好的再现缸内各主要组分的变化趋势，因此该简化机理是合理的。通过对比分析不同工况下的HCCI发动机条件下燃烧生物柴油替代混合物的详细机理和简化机理，可以发现：随着发动机初始温度的提高，可以使着火提前，缸内温度升高，但压力变化不大；随着初始压力提高，可以使发动机着火提前，缸内压力升高，但温度变化不大；随着燃空当量比的增大，缸内温度和缸内压力均有所提高。更多还原

【Abstract】 In recent years, biodiesel has got high popularity in the world as a substitute fuelfor a new environmental diesel, it has similar physical and chemical properties to diesel,it does not only be the fuel of existed diesel, but have better emission performance thantraditional engine fuel. So biodiesel has great significance in reducing the oilconsumption and protecting the environment.Firstly, based on Methyl Decanoat (C₁₁H₂₂O₂) and n-Heptane （nC7H16） as analternative biodiesel fuels, it builds a691components, the3226elementary reactionsbiodiesel alternative fuels detailed chemical kinetic mechanism. It constructs a detailedchemical kinetic mechanism of biodiesel alternative fuels which including691components and3226elementary reactions. Followed it verifies the ignition delay timeof the detailed mechanism in the different working conditions of the shock tubeconditions is reasonable. Then through the cylinder combustion under the conditions ofHCCI engine calculate its cylinder pressure, the main emissions in different workingcondition to prove the building mechanism is reasonable, the results show that themechanism is able to simulate the combustion process of a combustion engine.Through the analysis of the bio-diesel alternative fuel combustion in HCCI enginecondition process, we can know that alternative fuels bio-diesel show two stage: lowtemperature combustion process and high temperature combustion process, and the twoheat transfer processes of the two stage is separated by the negative temperaturecoefficient region. In the low temperature stage, n-Heptane mainly throughdehydrogenation of dehydrogenated radical OH, HO2and oxygen process consumed;Methyl Decanoate not only through those two ways to deplete, it can be decomposedinto methyl ester, it has much less carbon atom number, the main reason is that that theenergy among chemical bonds in the internal structure of the dehydrogenation product（Methyl Decanoate） is unbalance.Through the analysis of the evolution of the N elements, we can know that in theprocess of change from N2to NO_Xwhich into the cylinder, the radical CH₃, OH, H, Oand O2are key intermediate substances, and by controlling the generation of theseimportant intermediate substances we can effectively reduce the NO_Xemissions in theexhaust gas.With the combined method of the sensitivity analysis and path analysis, the mechanism of biodiesel alternative fuel combustion is simplified, a simplified dynamicmodel is obtained with113components and306elementary reactions. With thecomparison of various shock tube and fire delay time of the detailed mechanism, it isfound that the simplified mechanism is able to coincide with the fire delay time of themethyl decanoate and n-heptane. Meanwhile, With the comparison of the simplifiedmechanism and the experimental mechanism of the biodiesel, the simplified mechanismis also able to coincide with the cylinder pressure and temperature and reproduce thevariation tendency of the main components, so the simplified mechanism is proper.The detailed and simplified mechanism of the biodiesel substitute fuels burned inHCCI engine are compared and analyzed, the results show:（1） fire can be ahead of timeand cylinder temperature rises and pressure changes seldom while inital temperature ofengine is increasing;（2） fire can be ahead of time and cylinder pressure rises andtemperature changes seldom while inital pressure is increasing;（3） cylinder pressureand temperature both increases while the equivalent ratio is increasing.更多还原