Abstract
Modeling chemical kinetics relevant to low-temperature combustion requires complete description of reactions involving critical species such as hydroperoxyalkyl radicals, Q˙OOH, which undergo competing unimolecular reactions and bimolecular reactions with O2. The balance of flux across the two pathways affects rates of chain-branching and depends on temperature, pressure, and oxygen concentration. Accordingly, the influence of [O2] on product formation from alkyl + O2 reactions and the subsequent fate of Q˙OOH and related products is central to the development of an accurate chemical kinetics mechanism. However, chemical reactions consuming Q˙OOH-mediated species are often simplified to such a degree that mechanism truncation error (uncertainty derived from incomplete reaction networks) becomes significant.For the specific purpose of determining the extent to which expanded sub-mechanisms ameliorate inaccuracies in model predictions resulting from mechanism truncation error, the present work integrates speciation measurements from jet-stirred reactor experiments on cyclopentane oxidation with modeling using an expanded detailed chemical kinetics mechanism. The experiments utilize vacuum ultraviolet-absorption spectroscopy and mass spectrometry for isomer-resolved speciation of intermediates produced from cyclopentane oxidation at 835 Torr from 500 – 1000 K. [O2]-dependent experiments were also conducted from 0.12 – 3.66 · 1018 molecules cm–3 at 825 K to examine the influence on species profiles. The expanded mechanism is produced by merging detailed sub-mechanisms for Q˙OOH-mediated species (cyclopentene and 1,2-epoxycyclopentane) produced using Reaction Mechanism Generator (RMG) with an existing detailed mechanism for cyclopentane.Model predictions using the expanded mechanism yielded improvements in species mole fractions for both temperature- and O2-dependence. Ignition delay time simulations were also conducted and show appreciable sensitivity in the negative-temperature coefficient region due to incorporation of the detailed sub-mechanisms due to influence on O˙H radical populations. Sensitivity analysis revealed reactions that merit theoretical rate calculations for additional improvements and include species such as H2O2 and species related to R˙ + O2 reactions of cyclopentene and 1,2-epoxycyclopentane.
Published Version
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