【作者】 潘鑫；

【导师】 盛利；

【作者基本信息】 哈尔滨工业大学 ， 物理化学， 2023， 硕士

【摘要】 飞行器马赫数不断的增大导致对航空发动机冷却系统有了更高的要求。目前采用吸热航空燃料作为冷却剂被看做是一种有效的冷却方法。航空飞行器主要通过航空煤油提供能量,航空煤油的性能会严重影响燃烧的效率。但是航空燃油在加热(150℃)的过程中会发生结焦反应,焦体会附着在管道内部,会严重影响到管道的换热情况,进而影响飞行器的安全性。而如何抑制航空煤油结焦一直是能源领域的重要课题,对于飞行器的安全运行至关重要。由于多环芳烃(PAHs)是结焦的前驱体,故本课题使用密度泛函理论(DFT),以晕苯分子为体系,从热力学和分子反应动力学两个角度通过计算无电场和有电场的作用下,体系的电子结构、反应的焓变、构型的能量及构建反应的势能曲线等进行分析,探索静电场对碳氢燃料燃烧过程中多环芳烃(PAHs)成核的影响。静电场可以通过影响化学反应性对化学反应进行有效的控制,且静电场目前也是一种最清洁的催化剂,可以作为催化剂增强或抑制化学反应的反应速率。因此,本课题选择静电场作为一种调控手段,运用密度泛函理论,以多环芳烃(PAHs)代表物晕苯分子为代表,在CAM-B3LYP/6-31G(d,p)水平下计算无电场和静电场时晕苯成核的焓变、势能面、分子结构,探索静电场对晕苯成核的影响,以此达到利用静电场调控晕苯成核的目的。经过文献中分子动力学模拟研究表明,静电场在成核过程中主要是通过物理堆叠成核及化学键合成核两种方式。基于此对晕苯两种不同方式成核进行分析。研究发现,晕苯物理堆叠成核是利用晕苯间的π-π相互作用,由于静电场会影响晕苯之间的滑移距离,故静电场对晕苯物理堆叠成核主要起到抑制作用;而对于晕苯化学键合成核,在沿与成键平行的方向施加电场时,静电场会起到抑制晕苯分子的化学键合成核作用。在进行晕苯化学键合成核时,在不施加电场或沿不同方向施加不同强度的电场均以晕苯自由基与变形的晕苯五元环自由基键合为主。进一步利用密度泛函理论在CAM-B3LYP/6-31G(d,p)的计算水平下研究静电场对化学键合抑制机制,以望达到抑制结焦的目的。研究发现,在晕苯分子化学键合成核过程中,晕苯分子边缘六元环在高温的条件下会发生碳碳裂解和碳氢裂解。在静电场的作用下,晕苯分子会发生显著的极化现象,在一定程度上抑制晕苯分子脱氢。而在高温的条件下,晕苯分子的边缘六元环会发生碳碳键的断裂,而后形成五元环/七元环。结果显示在静电场的作用下,会一定程度上促进稳定的六元环的裂解,而易于形成开环的五元环或七元环。并且在静电场的作用下,晕苯分子主要以向五元环转变为主,但受分子极化的影响,五元环的环张力会变大,使得在该过程中晕苯分子会逐渐碎片化。从而在静电场的存在下会对晕苯的成核起到一定的抑制作用。本研究揭示了静电场对晕苯物理堆叠和化学键合成核的影响机制,为抑制航空煤油燃烧产生的多环芳烃的增长提供了有效的方法。更多还原

【Abstract】 Due to the increasing Mach number of aircraft,there are higher requirements for the cooling system of aircraft engines.At present,using endothermic aviation fuel as coolant is regarded as an effective cooling method.Aviation aircraft mainly provide energy through aviation kerosene,and the performance of aviation kerosene can seriously affect the efficiency of combustion.However,during the heating process of aviation fuel(150 ℃),coking reaction occurs,and the coke will adhere to the inside of the pipeline,which will seriously affect the heat transfer situation of the pipeline and thus affect the safety of the aircraft.How to suppress coking has always been an important issue in the energy field,which is crucial for the safe operation of aircraft.Since polycyclic aromatic hydrocarbons(PAHs)are precursors of coking,this topic uses density functional theory to analyze the electronic structure of the system,the enthalpy change of the reaction,the energy of the configuration,and the potential energy curve of the construction reaction under the action of without and with electrostatic field from the thermodynamic and molecular reaction kinetic perspectives,taking coronene as the system,to explore the influence of electrostatic field on the nucleation of polycyclic aromatic hydrocarbons(PAHs)in the combustion process of hydrocarbon fuel.Electrostatic fields can effectively control chemical reactions by affecting their reactivity,and currently electrostatic fields are one of the cleanest catalysts that can be used to enhance or suppress the reaction rate of chemical reactions.Therefore,this project chooses electrostatic field as a means of regulation.The enthalpy change,potential energy and molecular structure of coronene nucleation without and with electrostatic field are calculated at the CAM-B3LYP/6-31G(d,p)level by using density functional theory,taking coronene as the representative of polycyclic aromatic hydrocarbons(PAHs),to explore the influence of electrostatic field on coronene nucleation,so as to achieve the purpose of regulating coronene nucleation by using electrostatic field.According to the molecular dynamics simulation in the literature,the coronene nucleation is mainly through physical stacking and chemical bonding.Based on this,two different nucleation methods of coronene were analyzed.We found that physical stacking nucleation of coronene mainly utilizes the π-πinteraction between coronene.Due to the influence of electrostatic field on the slip distance between coronene,that is,the slip distance between coronene increases due to the increasing strength of the electrostatic field.Therefore,electrostatic field will mainly inhibit the physical stacking nucleation of coronene.For coronene chemical bonding nucleation,when electric field is applied in the direction parallel to the bonding direction,the electrostatic field will play a role in inhibiting coronene chemical bonding nucleation.In the process of coronene chemical nucleation,coronene radicals are mainly bonded to deformed coronene five membered ring radicals,both without electric field and under electric field in different intensities and different directions.Moreover,to inhibit coking,density functional theory is used to study the inhibition mechanism of coronene radicals chemical bonding under electrostatic field at the computational level of CAM-B3LYP/6-31G(d,p).It was found that carboncarbon cracking and carbon-hydrocarbon cracking occurred in the six membered ring at the edge of coronene at high temperature during the process of chemical bonding of coronene.Under electrostatic field,the dehydrogenation of coronene is inhibited at some extent due to significantly polarizing.Under high temperature conditions,the six membered ring at the edge of coronene will undergo carbon C-C breakage,and then form a five membered ring/seven membered ring.The results show that under the action of an electrostatic field,it will to some extent promote the cracking of stable six membered rings,while being prone to the formation of open five membered or seven membered rings.Under electrostatic field,coronene mainly transforms the radical with edged five membered rings,the tension of which increases due to the higher polarization,and promotes its fragmentation.Thus,in the presence of an electrostatic field,it will have a certain inhibitory effect on the nucleation of coronene.This study reveals the mechanism of the influence of electrostatic field on coronene physical stacking and chemical bonding,and provides an effective method to inhibit the growth of polycyclic aromatic hydrocarbons produced by combustion of aviation kerosene.更多还原