Full-scale fire testing of battery electric vehicles

Abstract

The market share of electric vehicles, powered by lithium-ion batteries (LIB), has been expanding worldwide with the global momentum towards green technology and improving the driving range on one full-charge. Studies are, however, still required on the fire safety of the latest but unmatured technology due to a distinctive phenomenon called thermal runaway. In this study, a series of full-scale fire experiments were conducted, focusing on the understanding of thermal behaviours of battery electric vehicle (BEV) fires. To provide up-to-date information on BEV fires, the latest BEV model with a high electric-energy capacity (64 kWh) was selected. For comparative analysis purposes, a LIB pack and a BEV body were tested individually after being physically disassembled. An internal combustion engine vehicle and a hydrogen fuel cell electric vehicle were also tested. During testing, the combustion of the BEV fires continued for approximately 70 min, resulting in critical measures of burning being determined; peak heat release rate (pHRR), total heat released (THR), fire growth parameter, and the average effective heat of combustion were measured to be 6.51–7.25 MW, 8.45–9.03 GJ, 0.0085–0.020, and 29.8–30.5 MJ/kg, respectively. It was also observed that the pHRR and THR were governed by the combustion characteristics of typical combustible materials in the passenger cabin, rather than by that of particular contents in the LIB pack with thermal runaway. Instead, a jet fire intensively discharging from the LIB pack led to a rapid flame spreading to adjacent combustible components of the BEV, thereby accelerating the fire growth. The findings could contribute to the activities of the first responders to BEV fire accidents, fire safety engineers, and structural member designers. This study also makes public the measured thermal quantities for further studies on the fire safety of existing or designing car-parking related structures.