The low-temperature dissolution characteristics of water in coal-based hydrocarbon fuels and its molecular dynamics simulation

Abstract

Context

As a substitute for traditional petroleum derived jet fuels, water in coal-based hydrocarbon fuels may precipitate into ice at low temperatures, leading to fuel system failures and endangering flight safety. This study employed Karl Fischer titration in conjunction with an optimized combination of an oil moisture detector to jointly measure the water solubility of coal-based hydrocarbon fuels at room temperature. The coefficient correction was performed on the oil moisture detector, and the water solubility curves of coal-based hydrocarbon fuels 233 to 313 K were finally measured and compared with other literature results. Due to the extremely low water content in actual fuel and the uneven distribution of water in the fuel, this study mainly considers the water enrichment zone in the fuel.

Methods

Materials Studio 2019 software was utilized to simulate a representative molecular model of coal-based hydrocarbon fuel and a molecular model of water. The positions and charges of the atoms were set and tested, with the COMPASS force field selected to describe interatomic interactions. This force field is the first de novo computing field capable of accurately predicting interactions between various molecules and polymers. Geometry optimization was performed in the Forcite module, and the Construction tool in the Amorphous Cell Tools module was used to construct a coal-based hydrocarbon fuel system. The two models consisted of 3674 and 3671 atoms, respectively, with initial dimensions of 33.2 × 33.2 × 33.2 Å, the boundary conditions are periodic boundary conditions, the energy of the two models is minimized, the conjugate gradient method is used as the optimization method, and then the NPT annealing and kinetic pre-equilibrium operations are carried out, and the molecular dynamics simulation is carried out after the system relaxes to steady state. Through the MD method, the macroscopic phenomenon of temperature decrease in coal-based hydrocarbon fuel systems was analyzed from a microscopic perspective using mean square displacement, diffusion coefficient, and radial distribution function. It was predicted that the crystallization process of coal-based hydrocarbon fuel systems was mainly around 248 to 258 K.