Abstract
Flame morphology is an important characteristic parameter for buoyant-controlled fuel diffusion flames. In this study, fire tests were conducted using rectangular burners placed against a thermally thin sidewall. Measurements were obtained for the flame morphology and temperature distribution on the back side of the sidewall. When the aspect ratio of the fire source was 7.45, flame branching into two regions was observed and was further evidenced by the temperature distributions on the corresponding two heated regions on the sidewall. The mechanism of the flame split was investigated, and numerical simulations and physical analyses were performed. The flame split occurred when the entrained air from the middle of the burner length was not consumed before it reached the bottom of the sidewall. Therefore, an appropriate ratio of flame height to burner length was proposed for the occurrence of the flame split. The critical ratio for the flame split was validated by other fire experiments of fire sources located against the sidewall.