Construction of macromolecular model of Shenmu lignite and study of its high-temperature combustion mechanism using ReaxFF MD simulation

Understanding the high-temperature combustion mechanism of lignite at the molecular level is crucial. In this study, a macromolecular structural model of Shenmu lignite was constructed and optimized based on industrial analysis, elemental analysis, X-ray photoelectron spectroscopy (XPS), and 13C solid-state nuclear magnetic resonance (NMR) experimental characterization data. Using Reactive Force Field Molecular Dynamics (ReaxFF MD) simulations with AMS software, the high-temperature combustion behavior of Shenmu lignite was investigated, with a focus on analyzing the impact of temperature on the combustion process, particularly the evolution of major gaseous products and reactive species in the temperature range of 2500 K to 4000 K. The ReaxFF MD simulation results indicate that an increase in temperature significantly accelerates the rate of O₂ consumption and increases the production of carbon dioxide (CO₂) and water (H₂O), suggesting a trend towards more complete combustion. However, at higher temperatures, CO production exhibits dynamic fluctuations, indicating incomplete oxidation and highlighting the complexity of radical-driven reaction pathways under these conditions. Additionally, the generation and consumption rates of reactive radicals (e.g., ·OH, ·O, ·H) also increase significantly with rising temperature, with the sustained generation of ·OH radicals at 4000 K contributing to the continuation of the combustion chain reaction.