Development and Investigation of a Safety Product Concept for E-Vehicle Battery Systems - The Development of an Emergency Cooling Spray-on System and the Test Method to Evaluate Its Performance
Examensarbete för masterexamen
Automotive engineering (MPAUT), MSc
There are three major types of abuse mechanisms when considering potential root causes for critical failure events of vehicle traction battery systems. All three may result in thermal runaway, i.e. exothermal decomposition of active materials inside battery cells unless any countermeasures are set in place. The focus in this report is to develop a safety system concept to prevent thermal runaway and a methodology to evaluate the performance of it. This report begins with a review of already existing safety systems. Based on the review, a safety system concept was developed followed by the development of a test rig to measure the cooling power of a spray-on cooling system; its functionality is presented in this report. The spray-on cooling system in this study is tested through physical experiments with two different cooling mediums: • Pure water mist • A mixture of 25% Ammonia(NH3)/75% Water(H2O) being applied as a mist Two spray nozzles with different nozzle hole diameters are also compared in terms of their relative influence on the cooling efficiency, i.e. how the droplet size (which is affected by the nozzle hole diameter and spray pressure) affects cooling performance. A smaller nozzle at a given pressure will result in smaller droplets. Prior to physical testing, the cooling mediums’ cooling performance was evaluated based on latent heat of evaporation using the software Aspen Plus V7.3. The simulation results were then examined and validated by the physical experiments. The results generated presented that the 25% NH3/75% H2O mixture mist was 18.6% more efficient in cooling than pure water mist in a spray-on cooling system when considering temperatures between 90-150°C. Additionally, the freezing point of the mixture was evaluated using a temperature chamber, and the results proved that a mixture of 25% NH3/75% H2O can withstand at least -43°C before freezing. Tests with the two different spray nozzle diameters, provided that the cooling power of the larger was slightly higher. However the spray duration was increased by 294% using the smaller nozzle diameter instead of the larger. Based on these result it was concluded that the smaller nozzle diameter allowed for approximately 19.5% more energy to be absorbed than the larger, given a specific volume of cooling medium.
Farkostteknik , Hållbar utveckling , Termisk energiteknik , Transport , Vehicle Engineering , Sustainable Development , Thermal energy engineering , Transport