Flame structure and flashback process in hydrogen partially premixed flame

This paper investigated the flame structure and flashback process of partially premixed hydrogen-air flames within a single-nozzle swirl combustor featuring a short mixing length and side-wall fuel injection. Experimental characterization utilized simultaneous OH* chemiluminescence imaging and Particle Image Velocimetry (PIV), complemented by non-reacting CFD simulations to analyze internal nozzle flow and fuel distribution. Three distinct stable flame structures (V, M, and N-M) were identified, with their appearance dependent on global equivalence ratio and airflow velocity. The V-flame (low equivalence ratio) showed the largest flame angle and a single flame surface on ORZ. The M − flame (intermediate equivalence ratio) showed a narrower angle with an inner flame surface and an associated upstream-shifted inner recirculation zone (IRZ). The N-M flame (high equivalence ratio or low u_a) exhibited the narrowest angle, disappearance of the IRZ, and flame anchoring within the nozzle, indicating flashback. Transitions between three flames were analyzed. The V to M transition was primarily driven by the fuel distribution change with increasing equivalence ratio. Conversely, the M to N-M (flashback) transition depended on the balance between flow velocity and flame speed, leading to the displacement and dissipation of the IRZ. These results demonstrate that the interplay between fuel distribution and velocity fields, governed by the side-wall injection configuration in this short mixing length combustor.