Experimental and theoretical analysis on extension flame length of buoyancy-induced fire plume beneath the curved ceiling

The extension flame length is determined by the unburnt fuel mass flow after impingement and the varying buoyancy component along with the curved ceiling. However, the existing model cannot use these two factors to quantitatively describe the extension flame under the curved ceiling. To analyze the extension flame length of the buoyancy-induced fire plume under the curved ceiling, the experimental and theoretical investigation was conducted to analyze the upper extension flame along with the curved ceiling, and the influence of the unburnt fuel mass flow and the varying buoyancy component on the effective heat release rate after impingement was explored in this study. Besides, the prediction equation for the total velocity of the ceiling jet along with the curved ceiling was proposed based on the momentum balance equation. Assuming that there was a linear relationship between the velocity of the ceiling jet and the entrained air, the effective heat release rate was respectively described from the perspectives of the entrained air mass flow and the unburnt fuel mass flow. Based on the above expressions of effective heat release rate after impingement, a new global equation describing the extension flame lengths beneath the curved ceiling was proposed. The validation results show that the proposed equation has a good correlation with the extension flame lengths under the curved ceiling within the relative error range of 15%; therefore, this equation can be effectively applied in the fire protection engineering of the utility tunnel.