Oxidation mechanism of methane fuel blended with dimethyl ether/hydrogen/ammonia via ReaxFF molecular dynamics simulation

Abstract

Hydrocarbon fuels used in micropower systems offer significant advantages, such as high energy density, lightweight properties, and extended power supply duration, making them the focus of widespread interest. Methane is particularly favored due to its excellent combustibility, ease of preparation, and convenient storage. In this study, ReaxFF molecular dynamics simulation is employed to investigate the influence of three additives (dimethyl ether, hydrogen, and ammonia) on the combustion mechanism of methane fuel. Results show that the pathways of CH₄ mainly involve dehydrogenation and oxidation reactions. In CH₄/C₂H₆O system, dimethyl ether is predominantly consumed via two pathways: C–O cleavage and dehydrogenation. These pathways form a significant quantity of active free radicals (such as CH₃ and CH₃O). In the case of CH₄/H₂ combustion, hydrogen is consumed to provide H, OH, and HO₂ active free radicals via reactions such as H₂ + OH → H₂O + H, H₂ + O₂ → 2OH, and H₂ + 2O₂ → 2HO₂. In the combustion of CH₄/NH₃, ammonia initially undergoes a dehydrogenation reaction involving OH, O, and H free radicals, resulting in the formation of NH₂. Subsequently, 65.57 % of NH₂ undergoes further reactions to form H₂O₂N, while 16.39 % of NH₂ forms NH radicals. The presence of additives influences the final products in different systems. In the CH₄/C₂H₆O system, the final products include CO, CO₂, H₂, and H₂O. In the CH₄/H₂ system, the final products consist of CO, CO₂, and H₂O. Lastly, in the CH₄/NH₃ system, the final products comprise CO, CO₂, H₂, NO, NO₂, and H₂O.