Comparative investigations on fire behaviors induced by the thermal runaway of large-format batteries in open space and confined tunnel

Most previous work mainly focused on the fire behaviors induced by thermal runaway of small format lithium-ion batteries in open space, but very few studies presented the comparison of fire behaviors for large format batteries in open space and confined tunnel. A series of experiments were conducted using large-format lithium iron phosphate batteries with different capacities (50 Ah, 72 Ah, 86 Ah) in open space and confined tunnel. The fire behaviors of large format batteries under different space forms are compared and the temperature distribution in the confined tunnel for different stages of battery fires is analyzed. Whether for open space or confined tunnel, the fire behavior induced by thermal runaway of large-format lithium iron phosphate batteries exhibits four typical stages with external manifestations of the changes in flame shape, mass, flame length and surface temperature, but the detonation is observed after ignition in stage ② for confined tunnel. The mass loss rate, heat release rate, flame length, surface temperature and flame temperature for open space are larger than the corresponding values for confined tunnel, and these parameters in stage ② are greater than that in stage ③ due to the different fire plume mechanisms. However, the durations of stages ②–④ for open space are significantly shorter compared to those for confined tunnel. Moreover, a simplified model of radiative heat flux is established by the flame morphology. The radiative heat flux is weakened in the confined tunnel, and it is larger in stage ② than that in stage ③. Besides, the modified models for the maximum and longitudinal ceiling temperature are proposed for stages ②–③ for large-format lithium iron phosphate battery fires in the confined tunnel.