Insights into the co-combustion properties and NOx emissions of ammonia/dimethoxymethane via ReaxFF molecular dynamics and kinetic numerical simulations

Abstract

Dimethoxymethane (DMM) is a promising combustion enhancer for ammonia (NH₃) — a carbon-free fuel, attracting interest in sustainable energy applications. However, current kinetic models for DMM/NH₃ co-combustion fail to simultaneously capture laminar burning velocity (LBV) and ignition delay time (IDT). This study employs the ReaxFF molecular dynamics (RMD) simulations to explore NH₃/DMM co-combustion, under varying temperatures, DMM mixing ratios, and O₂ equivalence ratios, focusing on NO formation/consumption pathways. The RMD simulations reveal that the CO bonds in DMM are more favorable for cleavage than the NH bond in NH₃, generating methoxy and methyl radicals that initiate radical-chain propagation in NH₃ oxidation. A detailed kinetic model was developed based on RMD insights and prior studies, accurately capturing LBV and IDT under given experimental conditions. Simulations reveal a strong positive correlation between NO yield and DMM mixing ratio (0.2‒0.4), with an 18.4 % increase in peak NO concentrations as DMM content rises from 0.2 to 0.4 under stoichiometric conditions. This trend is attributed to that increasing the DMM mixing ratio suppresses NH and NH₂ formation while enhancing H, O, and OH, thereby promoting NH₃ oxidation and shifting nitrogen conversion toward NO formation channels.