Thermal runaway properties of power cells under tunnel scenarios: Impact of heating patterns and heating powers

Due to the rapid increase in the number of electric vehicles and tunnels in cities, combining the inherent safety defect of power cells, the thermal runaway risk of power cells in tunnels requires significant attention. Herein, an experimental exploration is carried out to unveil the thermal runaway properties of power cells at tunnel scenarios, whereby the impact of heating patterns (electric oven and plate) and heating powers is involved as well. Under the effect of various heating patterns, cells show quite different thermal runaway properties inside a tunnel. In the oven case, the cell is uniformly heated, leading to two instances of smoke/gas release, followed by ejection fire and stable combustion. Whereas, the cell under the plate pattern illustrates smoke/gas releasing only once, with no combustion occurring due to the relatively low surrounding temperature. In addition, the cell affected by a plate experiences a process of thermal runaway propagation, i.e., the left part of the cell encounters thermal runaway first and then propagates to the right part, with the severity of the thermal runaway increasing over time. The cell heated by an oven illustrates worse thermal hazards with a more dramatic temperature rise and heat release, though the associated smoke hazard is relatively mild. The thermal conductivity of the cells is calculated to be approximately 3800 W/(m·K). The power of electric ovens and plates shows little impact on the heat release, mass loss, and smoke release of cells during thermal runaway. Finally, the dimensionless temperature rise at specific positions along the tunnel ceiling exhibits an exponential reduction as the dimensionless position increases during thermal runaway.