Estimating the flame length and ceiling maximum temperature in a branched tunnel fire with sloped mainline before shunting

This study carried out a series of reduced-scale experiments to investigate the flame tilt behaviors and maximum ceiling temperature in branched tunnel with inclined upstream mainline region. The influence of bifurcation angles, longitudinal velocity and mainline slope on flame characteristics and maximum ceiling temperature was analyzed. Experimental results show that the flame extension length initially increases to peak value with ventilation velocity, then gradual decline with relative large ventilation velocity. There is a little gap occurred for flame extension length under different mainline slope. The flame tilt angle is slightly affected by the mainline slope. In contrast, ventilation velocity has a significant effect on flame tilt angle that initially increases, then remains constant with increasing of ventilation angle. The maximum ceiling temperature is higher with greater fire power but lower ventilation velocity. The bifurcation angle and mainline slope have a non-monotonic influence on maximum ceiling temperature that using sin α and v in correlates this impact to develop a predicted model for maximum ceiling temperature, which shows good agreement with experimental data. As a results of analysis, the new segmented mathematical quantification models for flame extension length and quantitative method for predicting flame tilt angle are further proposed. • Experimentally investigated the flame characteristics in branched tunnel with uphill mainline. • Analyzed and normalized the flame extension length and bending angle. • Quantified the effect of bifurcation angle and mainline slope on maximum temperature. • Proposed the mathematical quantification models for flame length and maximum temperature.