Atomistic insight into the effects of electrostatic fields on hydrocarbon reaction kinetics

Reactive Molecular Dynamics (MD) and Density Functional Theory (DFT) computations are performed to provide insight into the effects of external electrostatic fields on hydrocarbon reaction kinetics. By comparing the results from MD and DFT, the suitability of the MD method in modeling electrodynamics is also assessed. The electric field-induced polarization predicted by the MD charge equilibration method is in good agreement with various DFT charge partitioning schemes. Moreover, the effects of oriented external electric fields on the transition pathways of non-redox reactions are investigated. Results on the minimum energy path suggest that electric fields can cause catalysis or inhibition of oxidation reactions. Pyrolysis reactions are not affected due to the weaker electronegativity of the hydrogen and carbon atoms. In practice, the reaction kinetics is also affected by the applied external Lorentz forces and interatomic Coulomb forces, since they can increase or decrease the energy of collision depending on the molecular conformation. In addition, electric fields can affect the kinetics of polar species and force them to align in the direction of the field lines. These effects are attributed to the energy transfer via inter-molecular collisions and stabilization under the external Lorentz force. The kinetics of apolar species is not significantly affected, mainly due to the weak induced dipole moment even under strong electric fields. The dynamics and reaction rates of species are studied by means of large-scale combustion simulations of n-dodecane and oxygen mixtures. Results show that under strong electric fields the fuel, oxidizer, and most product molecules experience translational and rotational acceleration, mainly due to close charge transfers, along with a reduction in their vibrational energy, due to stabilization. This study will serve as a basis to improve the current methods used in MD and to develop novel methodologies for the modeling of macroscale reactive flows under external electrostatic fields.