Abstract:Aromatic hydrocarbon fuels, such as toluene, are important components in real jet fuels. In this work, reactive molecular dynamics (MD) simulations employing the ReaxFF reactive force field have been performed to study the high-temperature oxidation mechanisms of toluene at different temperatures and densities with equivalence ratios ranging from 0.5 to 2.0. From the ReaxFF MD simulations, we have found that the initiation consumption of toluene is mainly through three ways, (1) the hydrogen abstraction reacti… Show more
“…Figure 3 displays that there is significant difference in terms of the oxidation rate of toluene when the density of toluene is increased from 0.15 g/cm 3 to 0.35 g/cm 3 when no Efield is applied. Higher toluene density gives a significant boost to its oxidation rate, which is in agreement with previous studies 25 . However, when applying a Efield of 0.2 V/Å, there is no much difference in the oxidation rate of toluene, as the oxidation rate of toluene has already been greatly enhanced.Figure 3Evolution of the toluene and oxygen molecules at density ρ = 0.15, 0.35 g/cm 3 , Efield = 0, 0.2 V/Å (ReaxFF NVT-MD simulation, T = 2500 K, toluene/oxygen = 1:100).
…”
Section: Resultssupporting
confidence: 93%
“…Since then, it was also used to analyze the hydrocarbon oxidation 19–21 , material properties 22, 23 , and other complicated chemical reactions such as the pyrolysis and oxidation of benzene 24 , toluene 25 or n-dodecane 26 . For instance, Chenoweth 19 and coworkers investigated the initiation mechanisms and kinetics associated with the pyrolysis of JP-10 (exotricyclo[5.2.1.0 2, 6 ]decane), a single-component hydrocarbon jet fuel with ReaxFF simulations.…”
Section: Introductionmentioning
confidence: 99%
“…Cheng et al . 25 performed the ReaxFF reactive force field to study the high-temperature oxidation mechanisms of toluene at different temperatures and densities. Meanwhile, they further studied the details of kinetic analysis of the oxidation of toluene and obtained good Arrhenius behaviors.…”
The effects of external electric field (Efield) on chemical reactions were studied with the reactive molecular dynamics (ReaxFF MD) simulations by using the oxidation of toluene as a model system. We observed that Efields may greatly enhance the oxidation rate of toluene. The initial reaction time of toluene is also reduced remarkably in Efields. A stronger Efield leads to a faster oxidation rate of toluene. Further studies reveal that the applying of a Efield may result in the oxidation of toluene at 2100 K which is otherwise not able to happen when the Efield is not present. The oxidation rate of toluene at 2100 K in a Efield is comparable with the oxidation rate of toluene at 2900 K when the Efield is not applied. In addition, Efields were observed to significantly enhance the occurrence of the initial radical generation for different pathways of toluene oxidation but they do not seem to favor any of the pathways. Finally, Efields do not seem to enhance the polarization of toluene during its transition state, which suggests that a polarizable charge equilibration method (PQEq) method might be needed to take the effects of Efields into consideration.
“…Figure 3 displays that there is significant difference in terms of the oxidation rate of toluene when the density of toluene is increased from 0.15 g/cm 3 to 0.35 g/cm 3 when no Efield is applied. Higher toluene density gives a significant boost to its oxidation rate, which is in agreement with previous studies 25 . However, when applying a Efield of 0.2 V/Å, there is no much difference in the oxidation rate of toluene, as the oxidation rate of toluene has already been greatly enhanced.Figure 3Evolution of the toluene and oxygen molecules at density ρ = 0.15, 0.35 g/cm 3 , Efield = 0, 0.2 V/Å (ReaxFF NVT-MD simulation, T = 2500 K, toluene/oxygen = 1:100).
…”
Section: Resultssupporting
confidence: 93%
“…Since then, it was also used to analyze the hydrocarbon oxidation 19–21 , material properties 22, 23 , and other complicated chemical reactions such as the pyrolysis and oxidation of benzene 24 , toluene 25 or n-dodecane 26 . For instance, Chenoweth 19 and coworkers investigated the initiation mechanisms and kinetics associated with the pyrolysis of JP-10 (exotricyclo[5.2.1.0 2, 6 ]decane), a single-component hydrocarbon jet fuel with ReaxFF simulations.…”
Section: Introductionmentioning
confidence: 99%
“…Cheng et al . 25 performed the ReaxFF reactive force field to study the high-temperature oxidation mechanisms of toluene at different temperatures and densities. Meanwhile, they further studied the details of kinetic analysis of the oxidation of toluene and obtained good Arrhenius behaviors.…”
The effects of external electric field (Efield) on chemical reactions were studied with the reactive molecular dynamics (ReaxFF MD) simulations by using the oxidation of toluene as a model system. We observed that Efields may greatly enhance the oxidation rate of toluene. The initial reaction time of toluene is also reduced remarkably in Efields. A stronger Efield leads to a faster oxidation rate of toluene. Further studies reveal that the applying of a Efield may result in the oxidation of toluene at 2100 K which is otherwise not able to happen when the Efield is not present. The oxidation rate of toluene at 2100 K in a Efield is comparable with the oxidation rate of toluene at 2900 K when the Efield is not applied. In addition, Efields were observed to significantly enhance the occurrence of the initial radical generation for different pathways of toluene oxidation but they do not seem to favor any of the pathways. Finally, Efields do not seem to enhance the polarization of toluene during its transition state, which suggests that a polarizable charge equilibration method (PQEq) method might be needed to take the effects of Efields into consideration.
“…The parameterisation by Chenoweth et al (2008), originally developed for the high-temperature gas-phase oxidation of hydrocarbons, was adopted for this work. It has been used in various studies for simulating the thermal decomposition of hydrocarbon and carbohydrate compounds (Chenoweth et al 2009;Jiang et al 2009;Desai et al 2011;Salmon et al 2009a, b;Wang et al 2011;Liu et al 2011a;Cheng et al 2012). The uncertainties related to the ReaxFF approach in general, and the parameterisation by Chenoweth et al in particular, are acknowledged.…”
The kinetics and products of cellulose pyrolysis can be studied using large-scale molecular dynamics simulations at high temperatures, where the reaction rates are high enough to make the simulation times practical. We carried out molecular dynamics simulations employing the ReaxFF reactive force field to study the initial step of the thermal decomposition process. We gathered statistics of simulated reactive events at temperatures ranging from 1400 to 2200 K, considering cellulose molecules with different molecular weights and initial conformations. Our simulations suggest that, in gas-phase conditions at these high temperatures, the decomposition occurs primarily through random cleavage of the b(1 ? 4)-glycosidic bonds, for which we obtained an activation energy of (171 ± 2) kJ mol -1 and a frequency factor of 1:07 AE 0:12 ð ÞÂ10 15 s -1 . We did not observe dependency of the kinetic parameters on the molecular weight or initial conformation. Some of the decomposition reactions involved the release of low-molecular-weight products. Excluding radicals, the most commonly observed species were glycolaldehyde, water, formaldehyde and formic acid. Many of our observations are supported by the existing experimental and theoretical knowledge. We did not, however, observe the formation of levoglucosan, which is the dominant product in conventional pyrolysis experiments at much lower temperatures. This is understandable, since the high temperatures can force the dominance of radical reactions over pericyclic reactions. Nevertheless, our results support further use of ReaxFF-based molecular dynamics simulations in the study of cellulose pyrolysis.
“…Atomic charges are updated in a self-consistent way using the electron equilibration method. 22 The ReaxFF model has been successfully applied to study combustion and pyrolysis of n-alkanes, [22][23][24][25] aromatics, 22,26 and other hydrocarbons. 27,28 We can then anticipate that the comparison of the performance of ReaxFF with density functional theory (ωB97X-D) 30 and semi-empirical (PM7) 31 results can allow us to establish whether ReaxFF 22,23 can be reliable to study the evaporation/condensation processes.…”
The effects of conformerisation and internal molecular dynamics (IMD) of n-dodecane conformers on energy transfers between gas and liquid phases are investigated. Bond energies, Gibbs free energies of internal dynamics of a set of n-dodecane conformers, and energies of the molecules colliding with the surface of an n-dodecane nanodroplet are studied using quantum chemical calculations (DFT with B97X-D/cc-pVTZ and semi-empirical PM7) and ReaxFF method. The results of the analysis show that the accuracy of the methods increases as we move from the application of PM7 to the application of ReaxFF and then to DFT. Different temperature dependencies of internal Gibbs free energies of conformers in the gas and liquid phases are expected to affect the heat and mass transfer processes between them. The calculations for the gas and liquid (using the quantum solvation model; SMD) phases show significant differences in the internal dynamics of conformers and demonstrate an entropy-enthalpy competition in the evaporation/condensation of an ensemble of the conformers.
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