Condensed-Phase Property Estimates for Ethyl Nitrate Derived from Atomistic Equilibrium Molecular Dynamics Simulations

Author(s):

Jeffrey D. Veals, Joshua L. Lansford, Chiung-Chu Chen, and Christopher P. Stone

Abstract:

This study contributes to a broader program to develop ML-based methods that reduce the time and cost to expand the ARL’s detailed chemical kinetics library. To support future combustion modeling, we model properties of ethyl nitrate (EN), a key surrogate for more complex nitrate esters. We perform atomistic equilibrium molecular dynamics simulations with the AMBER force field under a constant number of particles, pressure, and temperature conditions. We estimate key condensed-phase properties over temperatures ranging from 193 to 600 K. These properties include densities, enthalpies of vaporization, and self-diffusion coefficients. Our findings, particularly the diffusion coefficients, serve as a basis for computing rate coefficients for elementary condensed-phase reactions, thereby advancing our understanding of EN’s condensed-phase reaction behavior. The enthalpy-of-vaporization estimates in this work, combined with gas-phase enthalpy-of-formation estimates from previous work, result in condensed-phase enthalpy-of-formation estimates ranging from −7.2 to −0.4 kJ/mol of measured values. Using the diffusivity data, we derive a hole-free volume function (PHFV(T)), indicating that condensedphase reaction rates are likely to be significantly lower than gas-phase rates at temperatures relevant to combustion (e.g., less than 5% at 500 K). These results inform ongoing development of multiphase modeling, specifically liquid- and gas-phase EN combustion.