Stabilization and Emission Characteristics of Gliding Arc-Assisted NH₃/CH₄/Air Premixed Flames in a Swirl Combustor

This paper investigates the effects of gliding arc (GA) discharge on the stabilization and emission characteristics of premixed NH₃/CH₄/air swirl flames under various ammonia contents, flow rates, and global equivalence ratios. First, the lean blowout (LBO) limits are measured. We find that although blending CH₄extends the LBO limit of the ammonia flame to 0.6-0.8, the GA discharge further remarkably extends it to 0.3-0.4. Then, the flow and flame structures are visualized by simultaneous OH planar laser-induced fluorescence and particle imaging velocimetry measurements. The results reveal that the discharge increases the OH radical concentration and expands the inner recirculation zone, leading to improved flame stability. Second, the NO_xemissions are investigated over a wide range of global equivalence ratios and ammonia contents. It is seen that the GA discharge slightly increases the NO_xemission by less than 7% at low NH₃contents (<0.6), which can be attributed to the thermal and OH-involved reaction pathway of NO_xformation. However, as the NH₃content further increases (which is accompanied by the rapid growth of the NO_xemission), the GA discharge effectively reduces the NO_xemission by up to 30%. This effect might be due to the more intensive NO_x-consuming reactions by plasma-induced NH₂radicals at a higher ammonia content, which is confirmed by the strengthened NH₂∗ chemiluminescence under GA discharge conditions. Finally, a chemical reactor network analysis gives reasonable NO_xpredictions without GA discharge and highlights the NO_x-reduction effects of NH₂radicals under high ammonia contents.