Towards predictive multidimensional modeling for industrializing microwave air plasma-based NOx formation

• We developed a predictive model for atmospheric air plasma for fertilizer applications. • We obtain good agreement with experimental data over a wide range of conditions. • Our modeling insights provide detailed mechanistic understanding of NO x production. • We highlight the need for active quenching at specific energy inputs > 100 kJ/mol. We present a fluid model for (near-)atmospheric pressure air microwave plasma that couples fluid dynamics, microwave field heating, thermal chemistry, and the transport of chemically reactive species. The model is validated against experimental data from [ 1 ], which investigated an open microwave torch for NO x formation from air at 0.65 bar and specific energy inputs below 52 kJ/mol. The laminar model accurately reproduces the temperature profile, while both the laminar and turbulent models show excellent agreement with experimental results for NO x production. Additional validation is performed using the experimental results of [ 2 ] at atmospheric pressure, encompassing a broad range of flow rates (5–90 slm) and specific energy inputs (10–300 kJ/mol). For both laminar and turbulent flow, the model demonstrates good agreement with experimental measurements of core electron densities and NO x concentrations at the outlet. Furthermore, analysis of the simulation results provides detailed insights into the mechanisms of NO x formation and quenching within the plasma and its effluent. These insights highlight the benefits of high operating pressures and, for specific energy inputs above 100 kJ/mol, the need for rapid quenching beyond passive wall cooling. As the model does not rely on experimental data for parameterization, it offers predictive capabilities that make it a valuable tool for model-driven plasma reactor design.