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生物柴油燃烧过程化学动力学机理研究

发布时间:2018-06-07 11:11

  本文选题:生物柴油 + 化学动力学 ; 参考:《南昌大学》2015年硕士论文


【摘要】:生物柴油具有含氧10%~15%、动力性和经济性好、可再生性等优点,柴油机燃用生物柴油,大大降低了柴油机排放,特别是碳烟的排放,可以很好的缓解日益严重的能源危机和环境危机。“均质压燃、低温燃烧”本质上是湍流混合与化学动力学耦合作用的有限反应速率的化学动力学理论。深入研究生物柴油燃烧化学动力学对于发展这一新技术具有重大推进作用。本文首先构建了生物柴油替代物化学动力学模型,利用CHEMKIN PRO射流反应器模型对生物柴油替代物高低温反应动力学进行研究。替代物脂肪酸甲酯低温阶段主要通过OH自由基脱氢生成烷酯基,烷酯基发生一次加氧、异构化、二次加氧、分解生成OH活性基和含氧组分的低温链分支反应。构建了主要组分高低温反应路径图,从键能、环张力和反应势垒等角度分析了甲酯基及C=C对生物柴油燃烧氧化特性的影响,分析了脂肪酸甲酯氧原子迁移历程。利用均质密闭反应器模型对生物柴油着火延迟进行计算,分析了初始温度、压力、当量比以及C=C对生物柴油滞燃特性影响的反应动力学机理。脂肪酸甲酯组分长达18~20个碳原子的直碳链结构及含氧甲酯基特殊结构使得生物柴油十六烷值要比石化柴油高,反应系统OH活性组分浓度峰值提前出现致使着火提前。C=C的存在影响了邻近碳原子处的C-H及C-O2键离解能,进而影响其脱氢反应、一次加氧有效性及低温链分支反应,而且C=C数量越多以及C=C位置越靠近脂肪族碳链中心位置对低温活性的抑制作用越大,滞燃期越长。最后构建了生物柴油多环芳香烃PAHs生成与氧化动力学模型,利用反射激波管模型对混合燃料PAHs生成进行模拟。随着生物柴油体积分数的增加,燃烧过程O、OH自由基峰值浓度增大,促使更多的C2H2、C3H3被氧化形成稳定的CO2。另外,甲酯基中非羰基与羰基氧使更多的碳原子在低温阶段转化为稳定的CO2,导致了C2H2、C3H3生成量减小,抑制了第一个苯环以及PAHs的形成。而C=C使生物柴油低温燃烧过程小分子不饱和组分生成量增加,促进C2H2、C3H3的生成,导致PAHs的生成量增加。
[Abstract]:Biodiesel has many advantages, such as high oxygen content, good power and economy, reproducibility, and so on. Diesel engines burn biodiesel, which greatly reduces diesel engine emissions, especially soot emissions. It can alleviate the increasingly serious energy crisis and environmental crisis. "homogeneous compression ignition, low temperature combustion" is essentially a theory of chemical kinetics of a finite reaction rate coupled with turbulent mixing and chemical dynamics. The further study on the combustion chemistry kinetics of biodiesel is very important for the development of this new technology. In this paper, the chemical kinetics model of biodiesel substitutes was constructed, and the kinetics of high and low temperature reaction of biodiesel substitutes was studied by using CHEMKIN PRO jet reactor model. In the low temperature stage of the substitute fatty acid methyl ester, the alkyl ester group is mainly formed by the dehydrogenation of OH radical, and the alkyl ester group is oxidized, isomerized, oxygenated twice, decomposed to form OH active group and oxygen containing components. The high and low temperature reaction path diagram of main components was constructed. The effects of methyl groups and C on the combustion and oxidation characteristics of biodiesel were analyzed from the point of view of bond energy, ring tension and reaction barrier, and the oxygen atom migration mechanism of fatty acid methyl ester was analyzed. The ignition delay of biodiesel was calculated by using a homogeneous airtight reactor model. The reaction kinetics mechanism of the effects of initial temperature, pressure, equivalent ratio and Con C on the retarded combustion characteristics of biodiesel was analyzed. The cetane number of biodiesel is higher than that of petrochemical diesel because of the straight carbon chain structure of 18 ~ 20 carbon atoms of fatty acid methyl ester and the special structure of oxygen methyl ester group. The early occurrence of peak concentration of OH active component in the reaction system resulted in the early ignition of .CnC, which affected the dissociation energy of C-H and C-O2 bond near the carbon atom, and further affected the dehydrogenation reaction, the primary oxygenation efficiency and the low-temperature chain branching reaction. Moreover, the higher the amount of C, and the closer the position of C ~ (2 +) to the center of aliphatic carbon chain, the greater the inhibition of low temperature activity and the longer the ignition delay. Finally, the PAHs generation and oxidation kinetics model of biodiesel polycyclic aromatic hydrocarbons was constructed, and the PAHs generation of mixed fuel was simulated by using the reflective shock tube model. With the increase of the volume fraction of biodiesel, the peak concentration of O _ (OH) radical increases during combustion, and more C _ 2H _ 2C _ 3H _ 3 is oxidized to form stable CO _ 2. In addition, methyl ester non-carbonyl group and carbonyl oxygen make more carbon atoms convert to stable CO _ 2 at low temperature, resulting in the decrease of C _ 2H _ 2C _ 3H _ 3 production and the inhibition of the formation of the first benzene ring and PAHs. However, CnC increased the amount of unsaturated fraction of small molecule in low temperature combustion of biodiesel, promoted the formation of C2H2C3H3, and increased the amount of PAHs.
【学位授予单位】:南昌大学
【学位级别】:硕士
【学位授予年份】:2015
【分类号】:TE667

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