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Download fileEffects of New Ab Initio Rate Coefficients on Predictions of Species Formed during n‑Butanol Ignition and Pyrolysis
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posted on 2015-01-29, 00:00 authored by Darshan M. A. Karwat, Margaret
S. Wooldridge, Stephen J. Klippenstein, Michael J. DavisExperimental, time-resolved species
profiles provide critical tests in developing accurate combustion
models for biofuels such as n-butanol. A number of
such species profiles measured by Karwat et al. [Karwat, D. M. A.; et al. J. Phys.
Chem. A 2011, 115, 4909] were discordant with predictions from a well-tested
chemical kinetic mechanism developed by Black et al. [Black, G.; et al. Combust. Flame 2010, 157, 363]. Since then, significant theoretical and experimental efforts have
focused on determining the rate coefficients of primary n-butanol consumption pathways in combustion environments, including
H atom abstraction reactions from n-butanol by key
radicals such as HO2 and OH, as well as the decomposition
of the radicals formed by these H atom abstractions. These reactions
not only determine the overall reactivity of n-butanol,
but also significantly affect the concentrations of intermediate species
formed during n-butanol ignition. In this paper we
explore the effect of incorporating new ab initio predictions into
the Black et al. mechanism on predictions of ignition delay time and
species time histories for the experimental conditions studied by
Karwat et al. The revised predictions for the intermediate species
time histories are in much improved agreement with the measurements,
but some discrepancies persist. A rate of production analysis comparing
the effects of various modifications to the Black et al. mechanism
shows significant changes in the predicted consumption pathways of n-butanol, and of the hydroxybutyl and butoxy radicals formed
by H atom abstraction from n-butanol. The predictions
from the newly revised mechanism are in very good agreement with the
low-pressure n-butanol pyrolysis product species
measurements of Stranic et al. [Stranic, I.; et al. Combust. Flame 2012, 159, 3242] for all but
one species. Importantly, the changes to the Black et al. mechanism
show that concentrations of small products from n-butanol pyrolysis are sensitive to different reactions than those
presented by Stranic et al.
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H atom abstractionHO 2H atom abstraction reactionsignition delay timeOHNew Ab Initio Rate Coefficientsrate coefficientsproduction analysiscombustion environmentsbutoxy radicalsconsumption pathwaysH atom abstractionsmechanism showspecies time historiesspecies profilesab initio predictionscombustion models