Alcohol additives to enhance ammonia-methane combustion efficiency and reduce emissions: A reactive force field analysis

• Alcohol added combustion of ammonia/methane was explored using ReaxFF MD. • Alcohol additives altered NOx formation pathways to simpler ones. • Pyrolysis facilitated the decomposition of ammonia and methane. • Methanol and ethanol significantly impacted hydrogen bond energies of blends. Exploring the impact of alcohol additives on combustion and pyrolysis of ammonia/methane is of great importance in the pursuit of sustainable energy technologies. This work employs Reactive Force Field (ReaxFF) molecular dynamics (MD) simulations to investigate the underlying mechanism of how ethanol and methanol additives affect reaction pathways, NOx emissions and bond energy characteristics in ammonia-methane pyrolysis and combustion processes. It shows that adding alcohols altered NOx formation pathways, reducing the diversity of NOx and shifting the equilibrium toward simpler NOx such as NO and NO2. At 2,000 K, alcohol blends, particularly methanol, demonstrated a notable reduction in NO2 formation. At 3,000 K, both ethanol and methanol suppressed NO production, but the influence of methanol was stronger. Nitric acid production, HNO3, was present at lower temperatures but became negligible at higher temperatures because of the thermal breakdown of the higher-order NOx. These trends confirm that alcohol additives play a potential role in moderating NOx emissions and stabilizing reaction pathways. The pyrolysis in modified reaction pathways, which facilitated the decomposition of ammonia and methane in these blends, affected the formation of intermediate species, leading to the reduction in peak emissions. In addition, methanol and ethanol showed significant impacts on hydrogen bond energies of the mixture, especially key radicals such as CH2O, CH3, H2N, and CHN encouraging higher complexity pathways. By leveraging a computationally robust and scalable methodology, this study not only advances a fundamental understanding of alcohol-enhanced ammonia/methane combustion but also informs strategies to optimize these mixtures for practical use in modern propulsion systems.