Jiangsu Province Engineering Research Center of Fine Utilization of Carbon Resources, China University of Mining & Technology
School of Chemical Engineering and Technology, Key Laboratory for Green Chemical Technology of Ministry of Education, Tianjin University
College of Chemical Engineering, Shenyang University of Chemical Technology

采用B3LYP/6-311++G(d,p)和反应性分子动力学方法，对螺[4,5]-癸烷（C10H18）和螺[5,6]-十二烷（C12H22）的热解机理进行研究，揭示不同碳环结构和尺寸效应对燃料初始分解反应活性及小分子和芳烃产物生成行为的影响。结果表明，两种螺环烷烃燃料初始分解路径相似，均通过单分子碳碳键解离发生开环异构反应和小分子自由基进攻燃料母体的氢提取反应而消耗。相较于C10H18，C12H22中分子张力更大的七元环使速控步碳碳键及碳氢键能更低，导致燃料呈现出更低的初始分解温度和更高的反应活性。两种螺环燃料初始分解产生的自由基进一步影响了C1−C7小分子烃类和环烯产物的生成。其中，乙烯的生成始终占据主导地位。由于螺环尺寸效应的影响，链烃和环烯烃的生成表现出明显的结构差异性。对于C10H18分解而言，生成大量的五元环烯产物，包括环戊二烯、环戊烯、富烯、甲基环戊二烯和甲基环戊烯；而C12H22中更大的七元环结构，将生成对应的七元环烯产物（环庚烯、亚甲基环庚烷）。

Active cooling with high-energy-density liquid hydrocarbon fuel is one of promising techniques for the thermal protection of hypersonic aircrafts. To extend the flight range and increase the payload of volume-limited aerospace vehicles, high-energy-density liquid hydrocarbon fuel is directly used as an energetic additive or liquid propellant. Among them, biomass derived spiro-fuels, shown high density, low freezing point and high net heat of combustion due to compact molecular structures, are a kind of significant high-density fuel. The investigation of thermal pyrolysis of these spiro-fuels not only significantly improves the heat sink through the endothermic reaction, but also brings the new challenges of ignition and combustion of the cracked hydrocarbon fuel. The detailed theoretical calculations and molecular dynamics simulations of spiro [4,5] decane (C10H18) and spiro [5,6] dodecane (C12H22) initial pyrolysis were performed to explore the ring-size effect on the consumption of fuels and formation of primary products. The results show that the initial decomposition paths of the two spiro-fuels are very similar, mainly consumed by the open-ring isomerization via the unimolecular C−C dissociations of the six membered ring structure and H-abstractions by small radicals attacking the fuel parents. Due to the lower C−C and C−H bond dissociation energies caused by large tension of the seven membered ring structure, C12H22 may exhibit the lower initial decomposition temperature and higher reaction activity than C10H18. The differences of simultaneously formed fuel radicals during C10H18 and C12H22 initial pyrolysis further affect the formation pathways of C1−C7 small products, cycloalkenes and monocyclic aromatics. Among them, ethylene are the most important products. Due to the presence of inherent six membered rings in two spiro-fuels, monocyclic aromatics mainly originate from multi-step dehydrogenation reactions of fuel radicals, involving benzene, toluene, styrene and ethylbenzene. Notably, the size effect of spiro-ring in two fuels leads the obvious structural differences of the formation of chain hydrocarbons and cycloalkenes. For C10H18, a large number of penta- cycloalkenes may be generated, including cyclopentadiene, cyclopentene, fulvene, methylcyclopentadiene and methylcyclopentene, whereas the seven-membered ring structure of C12H22 may produce corresponding seven-membered products (cyclohexene and methylene cycloheptane). Moreover, the pyrolysis behaviors of these two spiro-fuels at 2000 K based on the ReaxFF molecular dynamics simulation were explored and show well consistent with the main products derived from DFT theoretical calculations. This work performs the DFT theoretical calculations and ReaxFF molecular dynamics simulation on the pyrolysis kinetic mechanisms of two representative high-density biomass fuels of spiro fuels, providing a possible initial pyrolysis path and laying a theoretical foundation for their practical application in engines. However, the complex working environment of the cooling channel poses more challenges to the actual pyrolysis process of the new high-density hydrocarbon fuels. In future research, pyrolysis experiments will be conducted under high temperature and high pressure conditions, and the detailed pyrolysis kinetics models with excellent predictive performance over a wide operating range will be constructed. At the same time, research will be conducted on the subsequent ignition and combustion process of the engine combustion chamber, exploring the impact mechanism of catalysts and fuel additives on this process, assisting in the practical application of fuel, improving fuel combustion efficiency, and effectively controlling pollutant emissions.

江苏省自然科学基金（BK20221134），国家自然科学基金（22208371）和江苏省双创博士（JSSCBS20221514）资助

王鸿燕, 孙欣悦, 周雨柔, 刘国柱, 王宇桐, 曹景沛. 螺[4,5]-癸烷和螺[5,6]-十二烷燃料热解机理及反应动力学研究[J]. 燃料化学学报（中英文）, 2024, 52(7): 1020-1034.

WANG Hongyan, SUN Xinyue, ZHOU Yurou, LIU Guozhu, WANG Yutong, CAO Jingpei. Study on pyrolysis mechanism and kinetics of spiro [4,5] decane and spiro [5,6] dodecane[J]. Journal of Fuel Chemistry and Technology, 2024, 52(7): 1020-1034.