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Proceedings of the Combustion Institute
Zador, Judit Z. ; Miller, James A.
Unimolecular pressure- and temperature-dependent decomposition rate coefficients of radicals derived from n- and i-propanol by H-atom abstraction are calculated using a time-dependent master equation in the 300-2000 K temperature range. The calculations are based on a C3H7O potential energy surface, which was previously tested successfully for the propene + OH reaction. All rate coefficients are obtained with internal consistency with particular attention paid to shallow wells. After minor adjustments very good agreement with the few available experimental results is obtained. Several interesting pathways are uncovered, such as the catalytic dehydration, well-skipping reactions and reactions forming enols. The results of the calculations can be readily used in CHEMKIN simulations or to assess important channels for higher alcohols. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Proceedings of the Combustion Institute
Prager, Jens ; Najm, H.N. ; Zador, Judit Z.
Theoretical methods to obtain rate coefficients are essential to fundamental combustion chemistry research, yet the associated uncertainties are largely unexplored in a systematic manner. In this paper we focus on the study of parametric uncertainties for a hydrogen-atom-abstraction reaction, CH 3CH(OH)CH3 + OH → CH3C (OH)CH3 + H2O, which bears significant importance in low-temperature alcohol combustion and especially in autoignition models. After identifying the parameters causing significant uncertainty in the rate-coefficient calculations, Bayesian inference is employed to determine the joint probability density function (PDF) thereof using the experimental data of Dunlop and Tully (1993) [6] on isopropanol + OH. The inferred PDFs are compared to the various parameter values obtained from high-level electronic-structure calculations in order to assess the limitations of current methodologies. To gain insight on modeling the kinetic isotope effect (KIE), the reaction of the hydroxyl radical with deuterated isopropanol is also investigated. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
8th US National Combustion Meeting 2013
Zador, Judit Z. ; Najm, H.N.
Optimization of new transportation fuels and engine technologies requires the characterization of the combustion chemistry of a wide range of fuel classes. Theoretical studies of elementary reactions - the building blocks of complex reaction mechanisms - are essential to accurately predict important combustion processes such as autoignition of biofuels. The current bottleneck for these calculations is a user-intensive exploration of the underlying potential energy surface (PES), which relies on the "chemical intuition" of the scientist to propose initial guesses for the relevant chemical configurations. For newly emerging fuels, this approach cripples the rate of progress because of the system size and complexity. The KinBot program package aims to accelerate the detailed chemical kinetic description of combustion, and enables large-scale systematic studies on the sub-mechanism level.
Welz, Oliver W. ; Zador, Judit Z. ; Savee, John D. ; Eskola, Arkke J. ; Sheps, Leonid S. ; Osborn, David L. ; Taatjes, Craig A.
Najm, H.N. ; Zador, Judit Z.
Najm, H.N. ; Zador, Judit Z.
Optimization of new transportation fuels and engine technologies requires the characterization of the combustion chemistry of a wide range of fuel classes. Theoretical studies of elementary reactions — the building blocks of complex reaction mechanisms — are essential to accurately predict important combustion processes such as autoignition of biofuels. The current bottleneck for these calculations is a user-intensive exploration of the underlying potential energy surface (PES), which relies on the “chemical intuition” of the scientist to propose initial guesses for the relevant chemical configurations. For newly emerging fuels, this approach cripples the rate of progress because of the system size and complexity. The KinBot program package aims to accelerate the detailed chemical kinetic description of combustion, and enables large-scale systematic studies on the sub-mechanism level.
Busemeyer, Brian D. ; Welz, Oliver W. ; Huang, Haifeng H. ; Zador, Judit Z. ; Taatjes, Craig A.
Zador, Judit Z. ; Huang, Haifeng H. ; Welz, Oliver W. ; Osborn, David L. ; Taatjes, Craig A.
Welz, Oliver W. ; Zador, Judit Z. ; Savee, John D. ; Sheps, Leonid S. ; Osborn, David L. ; Taatjes, Craig A.
Zador, Judit Z.
Physical Chemistry Chemical Physics
Welz, Oliver W. ; Zador, Judit Z. ; Savee, John D. ; Ng, Martin Y.; Meloni, Giovanni; Fernandes, Ravi X.; Sheps, Leonid S. ; Simmons, Blake S. ; Lee, Taek S.; Osborn, David L. ; Taatjes, Craig A.
The branched C 5 alcohol isopentanol (3-methylbutan-1-ol) has shown promise as a potential biofuel both because of new advanced biochemical routes for its production and because of its combustion characteristics, in particular as a fuel for homogeneous-charge compression ignition (HCCI) or related strategies. In the present work, the fundamental autoignition chemistry of isopentanol is investigated by using the technique of pulsed-photolytic Cl-initiated oxidation and by analyzing the reacting mixture by time-resolved tunable synchrotron photoionization mass spectrometry in low-pressure (8 Torr) experiments in the 550-750 K temperature range. The mass-spectrometric experiments reveal a rich chemistry for the initial steps of isopentanol oxidation and give new insight into the low-temperature oxidation mechanism of medium-chain alcohols. Formation of isopentanal (3-methylbutanal) and unsaturated alcohols (including enols) associated with HO 2 production was observed. Cyclic ether channels are not observed, although such channels dominate OH formation in alkane oxidation. Rather, products are observed that correspond to formation of OH via β-C-C bond fission pathways of QOOH species derived from β- and γ-hydroxyisopentylperoxy (RO 2) radicals. In these pathways, internal hydrogen abstraction in the RO 2 QOOH isomerization reaction takes place from either the -OH group or the C-H bond in α-position to the -OH group. These pathways should be broadly characteristic for longer-chain alcohol oxidation. Isomer-resolved branching ratios are deduced, showing evolution of the main products from 550 to 750 K, which can be qualitatively explained by the dominance of RO 2 chemistry at lower temperature and hydroxyisopentyl decomposition at higher temperature. © 2012 The Owner Societies.
Zador, Judit Z. ; Huang, Haifeng H. ; Welz, Oliver W. ; Osborn, David L. ; Taatjes, Craig A.
Sheps, Leonid S. ; Welz, Oliver W. ; Zador, Judit Z. ; Taatjes, Craig A.
Taatjes, Craig A. ; Welz, Oliver W. ; Zador, Judit Z. ; Sheps, Leonid S. ; Savee, John D. ; Osborn, David L.
Zeitschrift fur Physikalische Chemie
Kappler, Claudia; Zador, Judit Z. ; Welz, Oliver W. ; Fernandes, Ravi X.; Olzmann, Matthias; Taatjes, Craig A.
Although the propene+OH reaction has been in the center of interest of numerous experimental and theoretical studies, rate coefficients have never been determined experimentally between ∼600 and ∼ 750 K, where the reaction is governed by the complex interaction of addition, back-dissociation and abstraction. In this work OH time-profiles are measured in two independent laboratories over a wide temperature region (200-950 K) and are analyzed incorporating recent theoretical results. The datasets are consistent both with each other and with the calculated rate coefficients. We present a simplified set of reactions validated over a broad temperature and pressure range, that can be used in smaller combustion models for propene+OH. In addition, the experimentally observed kinetic isotope effect for the abstraction is rationalized using ab initio calculations and variational transition-state theory. We recommend the following approximate description of the OH+C 3H6 reaction: C3H6+OH⇄C 3H6OH (R1a,R-1a) C3H6+OH→C 3H5+H2O (R1b) k1a(200K ≤ T ≤ 950 K;1 bar ≤ P) = 1.45×10-11 (T/K)-0.18e 460K/Tcm3 molecule-1s-1 k -1a(200 K ≤ T ≤ 950 K; 1 bar ≤ P) = 5.74×10 12e-12690K/Ts-1 k1b(200 K ≤ T ≤ 950 K) = 1.63×10-18 (T/K)2.36e -725K/T cm3 molecule-1s-1. © by Oldenbourg Wissenschaftsverlag, München.
Huang, Haifeng H. ; Welz, Oliver W. ; Zador, Judit Z. ; Savee, John D. ; Vasu, Subith V. ; Johnsen, Howard A. ; Osborn, David L. ; Taatjes, Craig A.
Journal of Physical Chemistry
Zador, Judit Z.
Zador, Judit Z.
Zador, Judit Z.
Zador, Judit Z.
Taatjes, Craig A. ; Welz, Oliver W. ; Zador, Judit Z. ; Simmons, Blake S. ; Savee, John D. ; Osborn, David L. ; Sheps, Leonid S.
Zador, Judit Z.
Zador, Judit Z.
Journal of Physical Chemistry A
Zador, Judit Z. ; Miller, James A.
Zador, Judit Z. ; Miller, James A.
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