Analysis of forced and intrinsic quenching in a plasma reactor for nitrogen fixation by use of three-dimensional simulations and experiments

Journal article, 2026

Microwave plasma reactors offer a promising route for sustainable nitrogen fixation, yet the efficiency of NOx production is often limited by fast backward reactions at elevated temperatures. This study employs three-dimensional CFD simulations, validated against experimental measurements, to investigate the impact of forced jet quenching on the thermo-fluid-chemical dynamics of NOx formation. A split-feed configuration (10 SLM tangential plasma feed plus 10 SLM impinging quench jets) is compared with a conventional single-feed system relying solely on intrinsic quenching. The quench jets reorganize the flow, intensify local turbulence, and impose sharp thermal gradients that rapidly cool the plasma tail region where gas temperature falls from ~3500 K to below 800 K upon injection, suppressing thermal NOx dissociation and stabilizing reaction products. Net reaction rates indicate that forced jet-quenching suppresses NOx destruction and sustains higher yield across 400–800 W microwave power. These gains are achieved without an energy-efficiency trade-off, as evidenced by lower specific energy costs. Parametric analysis identifies the influence of jet location: positioning jets too near the plasma core leads to incomplete stabilization, while farther downstream offers negligible gains. Overall, forced jet quenching emerges as a robust, controllable complement that augments the reactor's intrinsic quenching to boost yield and energy efficiency. The validated modeling framework provides mechanistic insight and shows how to identify the configuration-specific upper bound in performance for a given reactor design.