“…These recirculation zones also influence the sooting characteristics of the burner. Three sooting structures; namely, filled, donut-shaped, and ring-shaped structures, were observed in previous studies [2]. Those different sooting structures were achieved by diluting the fuel and oxidizer jets with nitrogen while maintaining the ethylene + N 2 and air + N 2 flow rates constant, which mean that the average velocities at the exit of the central fuel and annular oxidizer jets (the inlet to the burner) are also held constant.…”