Investigation of an Unsteady Flame Propagating in a Curved Duct

Knowledge of behaviors of flame propagating in a curved duct is of great importance to prevent damage in practical industry. In this study, the premixed propane/air flame propagating through a square cross-section duct with a 90° bend was investigated. The high video camera and schlieren image technique were used to record the development of flame front structure. Ionization probes were applied to capture the characteristics of the flow field. Two cases of ignition positions were performed in the experiments. When ignition in the horizontal section, a tulip flame was formed and transition to turbulent flame occurred in the horizontal section. A blunt flame front was kept in the bend and the turbulence intensity was enhanced. However, when ignited in the vertical section, the keen-edged flame tip moved quickly along the lower wall of the bend. The flame kept laminar in the vertical section and bend. Only some weak turbulence was formed in the horizontal section. And the fluctuation of flame velocity was suggested mainly due to the variation of flame front surface area and turbulent combustion.