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Abstract
Because of climate change and the energy crisis, significant research effort has been focused on the adoption ofcleaner and more efficient combustion technologies, such as
the homogeneous charge compression engine (HCCI). HCCI
engines operate at lower temperatures and equivalence ratios
than conventional spark ignition (SI) and diesel engines to
curb the production of NOX and soot. Because HCCI engines
rely on autoignition triggered by compression alone, detailed
chemical kinetics models are needed to accurately predict
global observables important to engine design, such as ignition delay time. In low-temperature combustion chemistry,
autoignition is driven by chain-branching pathways initiated
by O2-addition to alkylhydroperoxy (QOOH) radicals, which
form following H-abstraction from, O2-addition to, and isomerization of a fuel molecule. QOOH radicals also have chain-
propagating pathways, which compete with chain-branching
pathways initiated by second O2-addition to QOOH. Because
the steady-state concentration of QOOH is difficult to measure experimentally, direct products of QOOH are used as
proxies to infer QOOH reaction rates from steady-state experiments. Cyclic ethers are direct chain-propagating products of QOOH radicals. Steady-state concentrations of cyclic
ether isomers in combustion experiments are frequently used
to validate chemical kinetics mechanisms. As such, high
level theoretical rate coefficients are available for a variety of
QOOH cyclicether + OH reactions. However, the-steady
state concentration of cyclic ethers also depends on the rate of
consumption, which is usually chosen on an arbitrary basis.
This dissertation focuses on the consumption reactions
for alkyl-substituted four-membered cyclic ethers, or oxetanes,
including unimolecular decomposition following H-abstraction
and bimolecular reaction with O2. In addition, several preliminary chemometrics-based binary classification models were
constructed to aid in the identification of relevant combustion
intermediates with unknown VUV absorption spectra. The
key outcomes of the present work are the following. Ring-opening pathways frequently lead to species which are also
important intermediates in reaction mechanisms of other species.
Stereochemistry has a significant impact on the dominant pathways for
decomposition of cyclic ether peroxy radicals. Cyclic ether peroxy radicals can decompose via conventional QOOH-mediated
pathways. Finally, a class of ring-opening pathways linking
cyclic ether peroxy radicals to KHP and its decomposition
products was discovered.