A comparative analysis of plasma and hydrogen effects on premixed ammonia combustion

In this study, we use direct numerical simulations to investigate turbulent premixed ammonia flames assisted by non-equilibrium nanosecond plasma discharges and hydrogen addition. The results reveal the coupling effects of turbulence, the hydrogen concentration in the fuel blend, and plasma discharges on the microscopic structure of the flame and chemical pathways. It is found that the flame front assisted by plasma is more distributed, whilst 58 % less stretched when compared to the hydrogen-enriched un-assisted flame. Additionally, turbulence has more pronounced effects on the hydrogen-enriched flame, broadening the flame brush. A comparison of the reaction pathways contributing to the heat release indicates that turbulence shifts the key reactions producing heat from HNO+H⬄NO+H₂ and OH+H₂⬄H + H₂O to NH₂ dissociation reactions. Additionally, NOx emissions are more influenced by thermal effects in the hydrogen-enriched flame, with NO concentration being 35 % higher than in the plasma-assisted flame. The higher NOx emissions in the hydrogen-enriched flame are attributed to the higher concentration of H radicals, which react with HNO and produce NO.