A comparative study of effects of methane and hydrogen on ammonia combustion in air via reactive molecular dynamics

Abstract

Ammonia (NH3) is a promising substitute for fossil fuels to achieve the net-zero emission targets. To improve the combustion performance of NH3, reactive fuels are added to the NH3 combustion. In the present study, the combustions of NH3, CH4/NH3, and H2/NH3 in air conditions were simulated using a reactive molecular dynamics method. Results suggest that whether the addition of CH4 and H2 could accelerate the consumption of NH3 and reduce NOX emissions depends on the fuel ratio of the reactive gas (CH4/H2) and NH3 molecules. The acceleration of NH3 consumption is significant at low H2/NH3 fuel ratios and high CH4/NH3 fuel ratios, as the addition of H2 and CH4 lowers the activation energy for NH3 combustion. NOX emissions are mitigated at low H2/NH3 and CH4/NH3 fuel ratios but increase at high fuel ratios. The pathways for NOx generation and de-NOx reactions were identified. This study unveiled the mechanism via which the reactive fuels affect the NH3 combustion performance from an atomic perspective. The findings will be useful for the design of high-efficiency and low-emission combustion chambers in ammonia-powered energy systems.