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

Abstract

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 CH4 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 NOx emissions are investigated over a wide range of global equivalence ratios and ammonia contents. It is seen that the GA discharge slightly increases the NOx emission by less than 7% at low NH3 contents (<0.6), which can be attributed to the thermal and OH-involved reaction pathway of NOx formation. However, as the NH3 content further increases (which is accompanied by the rapid growth of the NOx emission), the GA discharge effectively reduces the NOx emission by up to 30%. This effect might be due to the more intensive NOx-consuming reactions by plasma-induced NH2 radicals 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 NOx predictions without GA discharge and highlights the NOx-reduction effects of NH2 radicals under high ammonia contents.