Experimental study on burning velocity, structure, and NOx emission of premixed laminar and swirl NH3/H2/air flames assisted by non-thermal plasma

This paper investigates the effect of dielectric barrier discharge (DBD) plasma on premixed laminar and swirl NH3/H2 flames by applying a coaxial DBD to the unburned gas mixture. We focused on analyzing the flame structure, burning velocity, lean blow-off limit, and NOx emission characteristics of premixed NH3/H2 flames in the presence and absence of plasma. The mechanism of plasma-enhanced burning velocity was revealed through kinetic simulations based on the CHEMKIN software. The results indicate that DBD plasma can reduce the laminar flame height and increase the laminar burning velocity (LBV). The chemical kinetic effect is dominant for the enhancement of LBV, while the effect of hydrogen generated from ammonia dissociation and ozone is relatively weak. DBD plasma can significantly change the structure of the swirl flames, while has a slight effect on extending the lean blow-off limits of the swirl flames. Finally, emission measurements indicate that DBD plasma increases the NOx emissions for both the premixed laminar and swirl NH3/H2 flames. This effect can be attributed to the reaction pathways involving of H and OH radicals for NOx formation. It is assumed that the effect of hydrogen and DBD plasma on stability and burning velocity is synergistic, while the effect of hydrogen and plasma on NOx emissions is competitive.