An experimental investigation on thermal runaway features of lithium-ion battery modules under tunnel scenarios

This work details an experimental study exploring the thermal runaway characteristics of lithium-ion battery modules in tunnel environments, which is particularly relevant given the increasing presence of electric vehicles in such settings. The research involves modules at different states of charge (25 %, 50 %, and 75 % SOC) and considers tunnels with various types of ceilings (arc and flat ceiling). Thermal runaway propagation exhibits three distinct layers, leading to three phases that impact module mass, radiation heat flux, extinction coefficient, flame temperature, and smoke movement within the tunnel. Furthermore, the investigation reveals that thermal runaway in a 75 % SOC module induces a visibility decline leading to the evacuation speed inside the tunnel being lower than that in a blind, and a temperature increase of about 49.8 °C within the tunnel. The dimensionless temperature rise in the arc-ceiling tunnel is observed to exponentially decrease with the increasing dimensionless position. As the module's SOC increases, a more severe thermal runaway hazard inside the tunnel becomes apparent. This results in a higher thermal runaway propagation rate, greater temperature rise, more severe ejection and combustion, and a more pronounced reduction in visibility within the tunnel. The ceiling's maximum temperature rise due to thermal runaway relates to both the tunnel's geometry and the heat release of the thermal runaway.