Direct Chemical Kinetics Studies of Elusive Intermediates in Combustion: Ketohydroperoxides

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

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.