【作者】 张鹏；

【导师】 罗忠敬（Chung K.Law)； 杨斌；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2018， 博士

【摘要】 能源危机与环境污染是当今世界面临的两大难题。低温燃烧作为一种高效清洁的燃烧方式是解决这些难题的重要手段。不同于传统的燃烧方式,低温燃烧受控于燃料的燃烧反应动力学。因此研究低温燃烧技术需首先构建燃料的燃烧反应动力学机理。这些机理包含成千上万个反应,实验研究是给定其速率常数的重要方法。而目前的速率测量手段尚不能覆盖中低温段这一低温燃烧的核心温度范围。本工作的主要目标即探索将快速压缩机(RCM)用于测量中温段反应的速率常数。首先搭建了一套高压中低温RCM实验装置。该装置可覆盖压缩终点工况范围为650-1100 K、5-100 bar,同时配备快速取样系统,可以用于研究燃烧过程中的中间产物。使用该RCM对第一级着火延迟进行研究,分别观测到了异辛烷和甲基环己烷第一级着火的负温度系数(NTC)现象。结合模型分析,揭示了造成了第一级着火NTC现象的原因是五类反应与低温链分支通道的竞争。提出了一种基于RCM的基元反应速率测量方法。基于一个可用的详细机理,分析找到复杂体系中的简单子体系,使某可测组分的浓度不确定性由待测反应的速率不确定性主导,如此则可通过测量该组分的浓度曲线来约束该反应的速率常数。使用这一方法研究了甲酸甲酯分解生成甲醇和一氧化碳这一已知反应,通过实验测量一氧化碳浓度曲线,得到了该反应在30 bar和948-1112 K范围内的速率常数,与文献实验和理论计算结果取得了较好的一致性,由此说明了这一方法的可靠性。利用上述方法在30 bar和994-1068 K范围内研究了碳酸二甲酯热解体系中的两个重要的单分子反应。通过测量该体系中的二甲醚的浓度曲线获得了碳酸二甲酯分解生成二甲醚和二氧化碳这一反应的速率常数;通过测量乙烷浓度得到了碳酸二甲酯碳氧键断键反应的速率常数,二者与理论计算结果的一致性较好。实验结果对碳酸二甲酯热解模型的发展提供了理论支持。使用同样方法研究了1,5-己二烯与烯丙基反应生成丙烯和2,5-二烯-1-己基这一双分子反应。通过在25 bar和893-1007 K范围内测量1,5-己二烯热解体系中的丙烯浓度获得了该反应的速率常数。并通过分析文献中1,5-己二烯的流动管和射流搅拌反应器实验结果,将速率常数测量的温度范围扩展至776-1007 K,由此拟合得到该反应的速率常数。测量结果与现有理论计算有较好的一致性,为更进一步的理论研究提供了参照。更多还原

【Abstract】 Energy crisis and environment pollution are two main issues threatening our world.High-efficiency low-emission combustion technologies are developed to address these issues.Detailed combustion kinetics model is crucial for developing engines equipped with these technologies.These kinetics models typically consist of thousands of reactions,in which the rate constants are often determined by analogy,theory,and experiment.Among the three methods,experiment is the most decisive method and always being used as a benchmark of other methods.However,current experiment facilities are unable to cover the intermediate temperature range,which is a major concern of the advanced engine technologies mentioned above.Rapid compression machine（RCM）is a facility that already being widely used in the study of some important phenomena happening in the intermediate temperature range,such as negative temperature coefficient（NTC）regime,knock,and auto-ignition.Therefore,the aim of this work is exploring the possibility of using RCM in measuring reaction rate.A RCM operating at 650-1100 K and 5-100 bar was built in this work,featuring with a large bore and a large clearance height.Additionally,it was equipped with a heating system to elevate the initial temperature up to 200℃,and a fast sampling system coupled with a gas chromatograph to quantify intermediate species in pyrolysis or combustion studies.With the newly developed RCM,the NTC regime of the first-stage ignition was observed in the study of iso-octane and methyl-cyclohexane.Five reaction classes competing with the low temperature branching channel were identified of importance for this NTC regime.The first-stage NTC was regard as one of the two main reasons for the NTC of total ignition.With the RCM and the fast sampling system,a new method measuring reaction rate was proposed in this work.The main idea is that when the uncertainty of the concentration of a species is dominated by a single reaction,the rate of this reaction can be derived by measuring the concentration profile of this species.As a validation of the proposed method,the rate of the reaction CH₃OCHO（methyl formate,MF）=>CH₃OH+CO was determined by measuring the CO concentration in the MF pyrolysis in 948-1112 K,yielding a reaction rate consistent with previous experimental and theoretical studies.A unimolecular reaction,which is CH₃OCOOCH₃（dimethyl carbonate,DMC）=>CH₃OCH₃（dimethyl ether,DME）+CO₂,was studied by measuring DME concentration in the DMC pyrolysis in 994-1068 K.The optimized reaction rate agrees well with the RRKM/Master Equation calculation based on a high level quantum chemical potential energy surface,which casts more doubts on the previous calculation,which claimed a reaction rates of 4-5 times faster than the current study.Additionally,the reaction rate of DMC=>CH₃COO+CH₃ was derived by matching the measured ethane profile,resulting in a reaction rate consistent with experimental and theoretical studies in literature.A bimolecular reaction,which is 1,5-hexadiene+allyl radical=>hexa-2,5-dien-1-yl+propene,was studied by measuring propene concentration in the 1,5-hexadiene pyrolysis in 893-1007 K in RCM.Using the similar approach,flow reactor（FR）measurement at 776-833 K and jet stirred reactor（JSR）measurement at 800-875 K were adopted from literature to constrain the rate coefficients of this reaction as additional information.We finally generalize the rate coefficients measured by the RCM,FR and JSR to obtain an Arrhenius expression valid for 776-1007 K.Compared with the previous theoretical prediction computed at a moderate theoretical level,our measured reaction rates are⁵0%slower but are still located within the stated uncertainties.更多还原