Effects of H2O on NH3 combustion in air: A reactive molecular dynamics study

T Li and J Wang and YS Hong and YQ Liu and JY Zhu and XZ Jiang, JOURNAL OF THE ENERGY INSTITUTE, 121, 102184 (2025).

DOI: 10.1016/j.joei.2025.102184

Ammonia (NH3) emerges as a new clean energy alternative to fossil fuels, with incomplete combustion resulting in the formation of nitrogen oxides (NOx). The present study investigates the potential of water (H2O) to mitigate NOx emissions during the NH3 combustion. Reactive force field molecular dynamics simulations are employed to systematically analyze the impact of H2O on NH3 combustion in air, and the results are compared with the oxidation of NH3 under dry air conditions. The research systematically analyzes the effects of H2O blending ratios on NH3 consumption rates, intermediate species, and NOx formation, with a particular focus on the influence of H2O on the NOx formation pathways. Key findings reveal that the addition of H2O significantly enhances the oxidation rate of NH3 in the temperature range of 2400-2800 K, while the promotional effect can be neglected at high temperatures. Optimal H2O/NH3 blending ratios (0.5-0.75) effectively promote the generation of OH radicals, thereby accelerating the oxidation of NH3. Notably, the introduction of H2O initiates new nitrogen transformation pathways, modifying the NOx formation mechanism and influencing the NOx emissions. Detailed analysis indicates that the optimal H2O/NH3 mixing ratios suppress the NOx emissions by inhibiting the HNO-to-NO conversion. This study provides theoretical support and scientific insights into the regulation of NOx emissions through H2O modulation in NH3 combustion processes.

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