燃烧过程中碰撞传能及模式选择反应问题的研究

In engine combustion, there are many of the interactions among the different components and the intermediate products of the fuel. From a microscopic viewpoint, these interactions are realized by various collision processes. Usually, in a simulation, the vibrational-rotational states of the molecules is assumed to get the equilibrium distribution directly after a collision. While for the hydrocarbon fuel, vibrational-rotational states of the molecule needs too long time to get equilibrium distribution comparing with the period of the engine combustion, especially for the case of the excitation of CH or OH bond. Additionally, many of elementary reactions have a strong mode-specific feature. So the study of energy transfer and reaction in a collision process under the quantum state resolved level is very important for a wide range of combustion process. Currently, the study of quantum dynamics mainly focuses on the single-step reaction, but in a practical combustion, especially under the high pressure condition, the coupling effect between the corresponding reactions must be considered. Theoretically, the coupling effect must be described by quantum state resolved approaches. The project intends to use the multi-configuration time dependent Hartree method (MCTDH) and quasi-classical trajectory (QCT) method, combining with the reported potential energy surface and reaction force field (ReaxFF) to study the hydrocarbon fuel combustion. The collisional energy transfer, three-body effect, mode-specific reactions and the pressure dependent reactions will be mainly studied. While the corresponding application methods in the calculation of elementary reaction rate, the construction and simplification of combustion mechanism , the simulation of the ignition delay and the fuel design will be developed.

发动机燃烧涉及燃料不同组分之间、燃烧中间产物之间等众多的相互作用，微观上表现为不同组分间的相互碰撞，通常人们假设碰撞后分子的振转态迅速趋于平衡分布。但对含氢燃料，能级大的CH及OH键振动难以在发动机燃烧中达到平衡分布，且许多基元反应具有强烈的模式选择的特性，故研究碰撞过程中分子振转态分布的变化及其与后续反应的关系对宽温度和压力范围的燃烧过程很重要。目前，量子态分辨的研究多集中在单步反应碰撞，对考虑压力条件下不同反应间耦合的研究还非常少。本项目拟利用含时波包方法、多参考态含时动力学(MCTDH)和准经典轨线(QCT)方法，结合已有的精确势能面和反应力场（ReaxFF）研究碳氢燃料燃烧中重要的基元反应关联物间的碰撞反应、传能、模式选择及压力相关问题，考察多分子系统的三体效应及压力对反应速率常数的影响，探索碰撞传能及模式选择效应在基元反应速率、机理构建及简化、点火延迟、燃料设计方面的应用。

围绕重大研究计划宽温度压力范围反应动力学基础问题，通过本项目的研究，我们提出从微观量子态的层面理解燃烧动力学过程共性问题的研究策略，作为从分子水平或宏观流体水平理解燃烧过程的有效补充和扩展。量子态层面研究燃烧反应得到的结果可适用于任何外界环境、任何配比燃料，结果具有很强普适性。亮点工作有：（1）研究惰性气体分子与乙炔分子的碰撞传能过程，结果表明用LJ参数构造压力相关反应速率常数是较为可靠的。（2）研究了燃烧反应中亚乙烯基-乙炔异构化这一典型的1,2-氢转移过程，发现低能量振动模式更容易发生异构化的反常过程。（3）用动力学主方程理论构造完整的微波化学反应模型，支持用强微波调控燃烧反应的实际应用，用有易于产生、强度高等优点的微波辅助解决低温点火等问题是一个可行的方向。目前已在Science，Chemical Science，Nature Chem., JACS，PCCP，JPCA等杂志上发表9篇论文。