FEV, the global leader in the development of battery systems, says it has developed a novel combined simulation and testing process for the optimisation of the thermal propagation behaviour in automotive battery packs. This process can help to reduce the risk of injury and damage from battery cell thermal runaway, while also saving development time and cost.

Thermal runaway is a key safety aspect for hybrid and electric vehicles, with battery fires representing a threat to harm people, buildings, and the environment. The first thermal propagation regulation is expected in January 2021, with the GB/T 38031 standard in China requiring a minimum of five minutes of warning for vehicle passengers before fire from a thermal event extends beyond the battery pack or battery venting gas enters the cabin. Other markets and regulatory bodies are expected to follow soon.

With this in mind, FEV is driving development of simulation techniques in combination with a cascaded testing approach to optimise automotive battery pack design to prevent thermal propagation and the risk of thermal runaway.

“FEV’s simulation-based approach to optimise for battery thermal propagation is paired with our battery design and development capabilities as well as battery testing capabilities at our world-class eDLP facility. This uniquely positions FEV to support the entire thermal propagation development process,” said Professor Stefan Pischinger, CEO of FEV Group.

The simulation-based approach begins after key CAD dimensions and pack geometries are defined in the base development phase. FEV has created two customisable models for this purpose. Multi-physics simulation is used to produce a model to evaluate and optimise thermal runaway of one cell and propagation between battery cells, as well as between battery modules. This model and its customisation for specific customer requirements allows for design optimisation and introduction of countermeasures such as heat barriers. In parallel, a second, fluid-based venting gas model is customized, which is used to assess and optimise the design of the venting paths, dimensioning of venting valves as well as the indication of critical busbar routing inside of the battery pack.

The thermal and venting gas models are developed and then customised separately. Each model is validated further using physical test data. This testing approach is based on a step-by-step validation of cell to module to pack whereas on pack level different dummy packs are used to evaluate the thermal propagation behaviour. The cascaded testing approach can be optimised if any data (e.g. cell data) are already available. The advantage is that experimental data can be collected early in development without requiring the build of a fully functional battery pack, which saves time and cost.

After the models are validated with physical test data, the two models are then combined to create a comprehensive coupled model, containing the thermal battery model as well as local heat transfer coefficients and fluid/gas temperatures from the venting gas model. This combined model can be used for even more accurate and detailed simulation, which allows for a performance assessment and selection of optimized design parameters and variations. Finally, the design is tested and validated as a complete battery pack.

“Thermal propagation is clearly a safety concern for battery packs,” said Professor Pischinger. “FEV is proud to lead the way in the development of simulation approaches to address thermal propagation early in the development process for our customers.”