【作者】 刘波；

【导师】 罗胜年；

【作者基本信息】 西南交通大学 ， 机械（专业学位）， 2023， 硕士

【摘要】 传统化石燃料大量使用导致的环境污染和资源紧缺的现实问题是全球急需解决的共同难题。一个根本解决方法是寻求传统化石燃料的可替代燃料,走可持续发展之路。生物质液体燃料中的生物柴油因其低污染性和可再生性能够部分代替化石燃料,在现实需要及能源战略驱使下成为最具潜力的替代燃料,生物柴油的发展空间巨大。生物柴油是具有大分子尺寸(C16-C18)的复杂混合物,不饱和脂肪酸甲酯(fatty acid methyl esters,简称FAMEs)是其主要成分(超过70%)。直接研究生物柴油分子仍存在巨大挑战,因此,大量研究选择小尺寸FAMEs作为生物柴油替代品。但是,小尺寸不饱和FAMEs没有冷焰或负温度系数行为,因此,应寻找具有较长烷基链的不饱和FAMEs以作为研究生物柴油的替代品。因此,作为一个具有C=C双键的中等尺寸不饱和FAMEs,3-己烯酸甲酯(methyl-3-hexenoate,简称mhx3d)是研究真实生物柴油的十分有价值的替代品。研究mhx3d对揭示生物柴油的燃烧特性具有特别意义。在500-2000 K,我们选择最重要的两种自由基(H、OH)去研究mhx3d氢提取和加成反应动力学,以探索生物柴油燃烧动力学特性。用表现良好的M06-2X/ma-TZVP理论方法来评估mhx3d+H/OH体系的优化结构、多结构扭转、势能曲线以及直接动力学,用多结构变分过渡态理论结合小曲率隧穿方法计算体系速率系数。然后探讨了多结构扭转非谐、变分、隧穿效应和反应能垒对速率系数及分支比的影响,分析了氢键对体系的作用以及各反应通道的竞争。结果表明,当500 K<T<1200 K时,H加成反应主导mhx3d+H体系;当1250 K<T<2000 K时,氢提取反应主导mhx3d+H体系,其中,烯丙基提取反应的竞争力最强。当500 K<T<900 K时,OH加成反应主导mhx3d+OH体系,并且OH加成反应出现明显的负温度系数行为;当950 K<T<2000 K时,OH氢提取反应主导mhx3d+OH体系,其中,烷基提取反应的竞争力最强。不可忽视隧穿、多结构扭转非谐、变分效应对mhx3d+H/OH体系的影响,尤其是多结构扭转非谐效应,它显著影响了 mhx3d+OH体系,提高了体系反应性。此外,对mhx3d+OH体系的每个反应,氢键在不同程度上降低了过渡态能量,由于熵效应减弱,体系的反应性降低。而且,氢键被发现降低了最低能量构象对总配分函数的贡献,使得具有稍高相对能量的构象具有最大的统计权重。最后,用三参数Arrhenius表达式对基元反应的速率系数进行拟合。本研究可以为建立3-己烯酸甲酯的机理模型提供理论数据,促进更高分子量的不饱和甲酯甚至真实生物柴油的燃烧反应动力学研究,这对指导实践有重要意义。更多还原

【Abstract】 The practical problems of environmental pollution and energy scarcity caused by the widespread use of traditional fossil fuels are urgent global challenges that need to be addressed.A fundamental solution is to seek alternative fuels for traditional fossil fuels and pursue sustainable development.Biodiesel in liquid biofuels,due to its low pollution and renewability,can partially replace fossil fuels.Driven by practical needs and energy strategies,biodiesel has become the most promising alternative fuel with huge development space.Biodiesel is a complex mixture with large molecular size(C16-C18),and unsaturated fat acid methyl esters(FAMEs)are the main components(more than 70%).Direct research on biodiesel molecules still poses significant challenges,and small sized FAMEs can be chosen as alternatives to biodiesel to reduce research difficulty.However,small sized unsaturated FAMEs have no cold flame or negative temperature coefficient behavior.Therefore,unsaturated FAMEs with longer alkyl chains should be looked for as alternatives for biodiesel research.Therefore,medium sized FAMEs with C=C double bonds,methyl 3-hexenoate(mhx3d),are considered valuable substitutes for studying real biodiesel,and have special significance in revealing the combustion characteristics of biodiesel.At 500-2000 K,two most important free radicals(H,OH)were selected to study the reaction kinetics of mhx3d hydrogen abstraction and addition,in order to explore the combustion kinetics characteristics of biodiesel.The optimized structure,multi-structure torsion,potential energy curve and direct dynamics of mhx3d+H/OH system were evaluated by M06-2X/ma-TZVP method,and the rate coefficient of the system was calculated by multi-structure variational transition state theory with small curvature tunneling method.Then,the effects of multi-structure torsional anharmonic,variational,tunneling effects,and reaction energy barriers on rate coefficients and branching ratios were explored,and the effects of hydrogen bonding on the system and competition of reaction channels were analyzed.The results indicate that,at 500 K<T<1200 K,H addition reaction dominates the mhx3d+H system;at 1250 K<T<2000 K,the hydrogen abstraction reaction dominates the mhx3d+H system,of which the allylic abstraction reaction is the most competitive.At 500 K<T<900 K,OH addition reaction dominated the mhx3d+OH system,and obvious negative temperature coefficient behavior was observed;at 950 K<T<2000 K,the OH hydrogen abstraction reaction dominates the mhx3d+OH system,and the alkyl abstraction reaction has the strongest competitiveness.The mhx3d+H/OH system is subject to tunneling,multi-structure torsional anharmonic,and variational effects,which cannot be ignored.Especially,the multi-structure torsional anharmonic effect significantly affects the mhx3d+OH system and improves its reactivity.In addition,for each reaction of the mhx3d+OH system,hydrogen bonding reduces the energy of the transition state in varying degrees,and the reactivity of the system is reduced due to the weakening of the entropy effect.Moreover,hydrogen bonding was found to reduce the contribution of the lowest energy conformer to the total partition function,making the conformer with slightly higher relative energy have the largest statistical weight.Finally,the rate coefficients of elementary reactions were fitted in terms of a three-parameter Arrhenius expression.This study can provide theoretical data for establishing the mechanism model of methyl 3-hexenoate,promote the research on combustion kinetics of unsaturated methyl ester with higher molecular weight and even real biodiesel,which is of great significance for guiding practice.更多还原