Numerical simulation of flame propagation characteristics of NH3/Air flames assisted by non-equilibrium plasma discharge

Nanosecond non-equilibrium plasma-assisted combustion technology emerges as a reliable novel approach to enhance the flame propagation speed of NH₃. In this study, we developed a zero-dimensional + one-dimensional (0-D+1-D) non-equilibrium plasma-assisted combustion model to investigate the impact of nanosecond pulse discharge on the freely propagating flame speed of NH₃/Air mixture. The results reveal that due to the plasma discharge, abundant intermediate species (N₂H₄, N₂H₃, NO, H₂O₂) are formed at the inlet and are subsequently transported downstream, facilitating flame propagation. As a result, the speed of the 1-D freely propagating flame increases, and the flame front is closer to the inlet compared to the non-plasma condition. The transport effect of H₂ is also evident, with high concentrations of H₂ from the inlet providing the basis for reactions at the flame front that promote combustion. Furthermore, after the initial mixture flows into the flame front, a slight increase in heat release is observed, but this increase occurs within a very limited distance. Notably, in the case of plasma, a stronger heat release is evident at the flame front. Moreover, with plasma, the peaks of OH, H, O, NH₂, and HO₂ are higher and earlier than those of the non-plasma case due to the transport and kinetic effects of plasma. Pathway flux analyses reflect significant changes in the production and consumption paths of the three components OH, H, and O, which are most important for consuming NH₃ due to plasma addition. The higher OH mass fraction promotes the chain reactions that consume NH₃, effectively enhancing the flame propagation speed.

Novelty and significance statement

This study introduces a novel 0-D+1-D nanosecond non-equilibrium plasma-assisted combustion model to examine the impact of nanosecond pulse discharge on NH₃/Air flame propagation. It uniquely analyzes the interaction between species at the inlet and flame front, highlighting the transport effects of plasma-generated intermediates (N₂H₄, N₂H₃, NO, H₂O₂, H₂) that enhance flame speed, with a detailed pathway analysis of key species (O, OH, H).