Experimental study on the heat transfer and flame scale characteristics of inclined tunnel fires under longitudinal ventilation

The dynamic behavior of leaked liquid fuel fires in inclined tunnels severely threatens structural safety and complicates personnel evacuation, while their combustion and smoke diffusion characteristics are subjected to the significant coupling effects of tunnel slope and longitudinal ventilation velocity. To explore the mass loss rate and heat feedback mechanism of such fires in longitudinally ventilated inclined tunnels, experiments were performed with n-Heptane fires under different tunnel slopes and longitudinal ventilation velocities of 0.5 to 3.0 m/s. The results show the different mass loss rate variation patterns of fuel fires in the tunnel inclination direction, while the longitudinal ventilation velocity significantly alters the flame combustion characteristics. Meanwhile, tunnel slope significantly modifies the smoke transport mode by altering the flow field pressure distribution, which redistributes the relative contributions of convective, radiative, and conductive heat feedback. Based on analyses of mass loss rate, smoke transport, and heat feedback redistribution, empirical correlations are established for flame-scale parameters at reduced scales herein. This study provides reference data and physical insights into the coupling effect of longitudinal ventilation velocity and tunnel slope in reduced-scale tunnel fires, thus supporting future large-scale experiments and model development.