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Abstract
Biofuels are promising alternatives to hydrocarbons because they reduce carbon emissions and are produced from sustainable sources. Chemical kinetics studies investigating reaction mechanisms of these fuels are crucial for their implementation in advanced combustion technologies, which rely on autoignition and operate at low temperatures (< 1000 K). Ethers are one class of chemical species that are important intermediates in the low-temperature oxidation of hydrocarbons and are also utilized as biofuels. For example, cyclic ethers are formed from unimolecular decomposition of hydroperoxyalkyl radicals, which competes with bimolecular reactions leading to chain-branching. However, discrepancies between measurements and model predictions of cyclic ether species profiles are ubiquitous in the literature and are caused, at least in part, by a lack of detailed consumption reactions. In this dissertation, reaction mechanisms of cyclic ethers produced from the oxidation of n-butane, namely ethyloxirane, cis-2,3-dimethyloxirane, trans-2,3-dimethyloxirane, and 2-methyloxetane, are elucidated using detailed chemical kinetics modeling and isomer-resolved speciation measurements. Chemical kinetics mechanisms for ethyloxirane and 2,3-dimethyloxirane are constructed using Reaction Mechanism Generator (RMG). Rate coefficients are subsequently refined for important reactions in the oxidation of cis- and trans-2,3-dimethyloxirane by performing quantum chemical calculations within the automated workflow of AutoMech. To provide modeling targets for the new mechanism, O2-dependent steady-state oxidation experiments are performed on the stereoisomers of 2,3-dimethyloxirane in a jet-stirred reactor (JSR). In addition, photolytically-initiated oxidation experiments are performed on 2-methyloxetane in a low-pressure flow reactor equipped with a multiplexed photoionization mass spectrometer (MPIMS). The purpose of these experiments is to investigate the competition between unimolecular decomposition and O2-addition of 2-methyloxetanyl radicals. Ethers are also valuable as a second-generation biofuel, which do not compete with agricultural food production. For example, 1,2-dimethoxyethane (CH3OCH2CH2OCH3) is a glycol ether with a high cetane number that improves the efficiency of diesel engines while also reducing particulate matter emissions. To study low-temperature oxidation mechanisms of 1,2-dimethoxyethane, photolytically-initiated and O2-dependent speciation experiments are performed in a high-pressure flow reactor with MPIMS detection. Steady-state oxidation experiments are also conducted using a JSR, which provide new modeling targets for 1,2-dimethoxyethane mechanisms.