The Hot Stuff is Often Dangerous - Solid Particles in AVL FIRE? M Thermal Runaway Simulation

by Dr. Lucas Eder

In AVL FIRE? M it is possible to introduce the Lagrangian Spray via a trigger based event. These “trigger-based” particles are part of the battery thermal runaway workflow, as they have a significant impact on the risk evaluation of hazard investigations. You can couple your thermal runaway simulations with the particles and – based on so called “risk indices” – evaluate your design with respect to the particles being additional ignition and arcing sources.

Why is it important?

Especially hazard scenarios of lithium-ion battery are a point of active research in academia and industry – not only to understand the relevant phenomena causing hazard scenarios but also how to mitigate them. One of the most critical scenarios is the non-reversible, self-heating of a battery entering a state of exothermic heat release – the battery thermal runaway. Exothermic reactions inside the battery cell cause rapid and violent release of hot and flammable gases and spontaneous combustion of said gases. Without suitable countermeasures, the released heat from one damaged cell can trigger a chain reaction and can cause further thermal runaway events of adjacent battery cells and or modules, potentially resulting in complete destruction of the battery pack and vehicle can be the consequence.

Particle exertion – describing the ejection of hot, molten particles of a battery cell during the thermal runaway event – is a very recent topic of research. These particles can contribute to a drastic risk increase during the thermal runaway event as the particles can serve as ignition sources for flammable venting gas, as well as to facilitate arcing.

How can you use it?

In the Spray module the start timing of the spray is linked to a trigger based event – similar to the additional heat- and mass sources.

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Interaction with the thermal runaway workflow

To increase the insight and potential predictiveness of 3D-CFD thermal runaway simulations, the introduction of particles with variations on size distribution and injection rates has been carried out in a battery module containing 12 prismatic battery cells. For the investigation variations were applied to the geometry. To provide qualitative and quantitative risk assessment, a mathematical formulation for a Risk Index, taking a relation of contained energy in particles and needed gas ignition energy, has been introduced and applied.

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Summary

The evaluation of results clearly shows significant risk reduction when the injection rate is changed. This can be explained by different amount of available particle matter and the different melting process of battery module cover, which could be shown using 3D analysis images. The developed method therefore clearly can provide additional insight due to the spatial and temporal resolution of particles within the context of thermal runaway simulations.

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As much as we love to nerd out about simulation and read lengthy articles about it, we have to cut it short at this point.

We want to thank Dr. Lucas Eder for the insights and the impressive work that is performed day to day behind the scenes.

Real-world activities and their real-time limitations bring this Simulation Saturday to an end, but stay tuned for another one soon!

Cheers, Thomas and Michael

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