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 NH 3 /CH 4 /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 CH 4 extends 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 x emissions are investigated over a wide range of global equivalence ratios and ammonia contents. It is seen that the GA discharge slightly increases the NO x emission by less than 7% at low NH 3 contents (<0.6), which can be attributed to the thermal and OH-involved reaction pathway of NO x formation. However, as the NH 3 content further increases (which is accompanied by the rapid growth of the NO x emission), the GA discharge effectively reduces the NO x emission by up to 30%. This effect might be due to the more intensive NO x -consuming reactions by plasma-induced NH 2 radicals at a higher ammonia content, which is confirmed by the strengthened NH 2 * chemiluminescence under GA discharge conditions. Finally, a chemical reactor network analysis gives reasonable NO x predictions without GA discharge and highlights the NO x -reduction effects of NH 2 radicals under high ammonia contents.