Numerical investigation of plasma-assisted MILD combustion of ammonia using a hybrid modeling approach

Plasma-assisted combustion (PAC) of ammonia (NH₃) has gained increasing interest in recent years, but detailed studies using computational fluid dynamics (CFD) techniques are still missing. This is due to the emerging nature of the field and the high computational cost associated with such simulations. This study proposes a comprehensive and efficient modeling approach to integrate plasma into multidimensional simulations. A reduced kinetics mechanism is first developed using an in-house code, which employs plasma-specific direct relation graph with error propagation (P-DRGEP). Subsequently, a combination of a commercial CFD code and an in-house zero-dimensional (0D) code, which simulates pulsed electric discharges, allows for the incorporation of the reduced kinetics mechanism with all the plasma-related species into the CFD code. This approach is applied to assess the impact of plasma on NH₃/air combustion in a cyclonic burner operating within the Moderate or Intense Low-oxygen Dilution (MILD) regime. Two different positions for the plasma discharge within the burner are investigated and compared. It is demonstrated that as the deposited power per pulse increases, the influence of plasma on the burner becomes more pronounced, leading to a significant reduction in nitrous oxide (N₂O) emissions and improved fuel conversion at the outlet of the burner. Additionally, an analysis of the extinction limits reveals that plasma enhances operational stability, sustaining stable NH₃ oxidation at much lower outlet temperatures compared to MILD combustion without plasma.