Structure–activity relationships and reaction mechanisms for future fuel components: Dialkyl ethers, oxymethylene ethers, and furanes

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Linear and cyclic ethers, as fuel components that can be produced from biomass or electrochemically, will play an important role in future combustion systems. Despite their importance, the understanding of their decomposition and combustion chemistry is insufficient. This important knowledge gap should be closed in this project by experimental and theoretical chemical kinetics investigations of dialkyl ethers, oxymethylene ethers (OMEs), and furanes under combustion-relevant conditions, i.e. at temperatures above 1000 K.For detailed modeling of combustion processes, hydrogen abstraction reactions represent a class of crucial importance. Therefore, the first part of this project aims at determining rate coefficients for H abstractions by OH radicals and H atoms for a series of selected linear, branched, and cyclic ethers by shock-tube experiments in combination with spectrometric techniques and interpretations by ab initio transition state theory (TST) calculations. Following the concept of group additivity, the combination of experimental and theoretical results aims to derive rate rules that enable the calculation of H-abstraction rate coefficients for all ether compounds. In the second part of the project, the pyrolysis of representative molecules of this substance class will be investigated in shock-tube experiments. On the one hand, shock tube experiments coupled with gas chromatography (GC/MS) and time-of-flight mass-spectrometry (TOF-MS), and on the other hand, flow reactor experiments coupled with GC/MS will be carried out to determine the composition of reaction products obtained during pyrolysis. As a result, the required kinetics information of the initial unimolecular reactions can be determined and important secondary reactions can be identified. With the help of experimental results and the Reaction Mechanism Generator (RMG) code developed by MIT, reaction models are being developed and optimized. An important contribution to this is provided by the rate rule expressions for the description of H-abstraction reactions.In this project, the complementary expertise of the Institute for Combustion and Gas Dynamics (IVG) of the University of Duisburg-Essen and the Institute of Combustion Technology (DLR Stuttgart) will be brought together. The experimental work on H abstraction by OH radicals, the time-resolved measurements by mass spectrometry, the flow reactor measurements, and the ab initio TST calculations are assigned to the IVG, while the experiments on H abstraction by H atoms in isotope-labeled components, the measurement of product compositions by shock-tube-experiments with GC/MS and the development of reaction mechanisms are assigned to the DLR Stuttgart.