Direct Chemical Kinetics Studies of Elusive Intermediates in Combustion: Ketohydroperoxides

为交通运输开发可持续能源技术仍然是一项重大的科学挑战，也是美国和世界其他国家的高度优先事项。考虑到目前和未来几十年对燃烧衍生能源的依赖，一个关键的挑战是提高下一代燃烧系统的效率。提高效率依赖于更好地理解控制发动机点火和放热过程的化学反应。两者对于优化用于模拟燃烧化学的预测模型都很重要。重要的是，这些模型的有效性取决于对详细实验数据的验证。因此，本研究的主要活动是研究一组以前未研究过的分子的基本化学反应，酮氢过氧化物，这是难以捉摸的中间体，也是理解点火过程的核心。目前研究的主要好处是发展了对与燃烧相关的化学反应途径和速率的新的基本理解，以及新的建模能力，以提高现有计算机模拟模型的鲁棒性。此外，该研究项目还包括对博士生和本科生退伍军人的科学培训，以及增加当地高中有关可持续交通能源的教育材料。本文的研究解决了中间物种酮氢过氧化物的分子结构与燃烧过程中产物形成之间的知识差距。为了实现这一目标，成立了一个跨学科的团队，在环己烷燃烧衍生的酮氢过氧化物的化学合成和物理化学方面具有专业知识。用两种不同的实验研究了三种异构体的反应：先进光源同步加速器的多路光离质谱，以及佐治亚大学高压射流搅拌反应器的物种形成。在实验的同时，利用“反应机理生成器”软件包生成了环己烷燃烧化学的新子机理。目前建模工作的推动力是单分子分解反应是当前燃烧模型中酮氢过氧化氢物质的唯一消耗途径。然而，烷基过氧自由基共有的其他反应途径也是可能的，包括与羟基自由基和氧的反应。随着反应途径的完整表征，现有的化学动力学模型的不确定性可以最小化，燃烧效率的准确预测。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The development of sustainable energy technologies for transportation remains a significant scientific challenge and a high priority for the United States and rest of the world. Given the current and projected reliance on combustion-derived energy for decades to come, a key challenge is increasing the efficiency of next-generation combustion systems. Improvements in efficiency relies on better understanding of chemical reactions that control ignition and heat-release processes in engines. Both are important in optimizing predictive models used to simulate combustion chemistry. Importantly, the efficacy of such models hinges on validation against detailed experimental data. Therefore, the primary activity of the research herein is the study of elementary chemical reactions from a previously unstudied set of molecules, ketohydroperoxides, which are elusive intermediates and central to understanding ignition process. The primary benefit of the present research is the development of new fundamental understanding of chemical reaction pathways and rates relevant to combustion as well as new modeling capabilities to improve the robustness of existing computer simulation models. In addition, the research project encompasses scientific training of Ph.D. students and undergraduate Student Veterans, as well as augmentation of local high school-level educational materials related to sustainable transportation energy. The research herein addresses the knowledge gap on the connection between the molecular structure of intermediate species ketohydroperoxides and products formation during combustion. To achieve this objective, an interdisciplinary team with expertise in chemical synthesis of ketohydroperoxides, derived from cyclohexane combustion, and physical chemistry is formed. Reactions of the three isomer species are studied using two different experiments: multiplexed photoionization mass spectrometry at the Advanced Light Source synchrotron, and speciation from a high-pressure jet-stirred reactor at the University of Georgia. In parallel to experiments, Reaction Mechanism Generator software package is used to generate a new sub-mechanisms for cyclohexane combustion chemistry. The impetus for the present modelling work is that unimolecular decomposition reactions are the only consumption pathways of ketohydroperoxide species in current combustion models. However, other reaction pathways common to alkylperoxy radicals are possible, including reaction with hydroxyl radicals and with oxygen. With complete characterization of reaction pathways, the existing uncertainties of chemical kinetics models can be minimized with accurate predictions of combustion efficiency.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.