Co-combustion characteristics of ammonia and ethanol: A combined ReaxFF-MD and DFT study

Abstract

Ammonia (NH₃), as a "carbon-free" hydrogen energy carrier, is an excellent alternative to traditional fuels. It can improve combustion efficiency when co-burning with ethanol (C₂H₅OH). However, the research on the co-combustion characteristics of these two substances at the microscopic level is still incomplete. Therefore, the methods of ReaxFF molecular dynamics simulation and density functional theory are adopted to explore the combustion mechanisms of NH₃ and C₂H₅OH. The calculation results show that C₂H₅OH first pyrolyzes thermally to generate free radicals such as ·OH and ·H, which promotes the oxidation of NH₃ through a series of hydrogen abstraction reactions. Among them, the ·OH free radical obtains a kinetic advantage with its lowest energy barrier, thus playing a major role in promoting the oxidation of NH₃. During the oxidation process, the amino group generates a variety of different intermediate products with the transfer of nitrogen elements, such as HNO, NH, and N₂H₄. The alkyl radicals ·CH₃ and ·C₂H₅ mainly participate in the subsequent cyanidation reaction with ·NH₂ and finally generate HCN. These findings provide mechanistic insights that support kinetic model development and nitrogen-species control strategies.