Abstract: This study addresses the critical urban safety issue of lithium-ion battery fires in electric bicycles by analyzing the influence of safety vent orientation on fire development through full-scale burning tests. Results show that e-bike fires generally exhibit three distinct stages in both tests: initial combustion, jet fire followed by stable combustion, and decay leading to extinction. The number of jet fire incidents is closely related to the number of battery cells, whereas the scale of jet flames shows no significant correlation with their sequence of occurrence. When the safety vent is oriented vertically (Test A), the flame temperature directly above it is significantly increased, with an average peak temperature of 181.8 ℃， approximately 16% higher than that observed in the horizontal orientation (Test B). Moreover, the entire e-bike in Test A is fully burned in a "rear-first, then front" pattern, where the front section is directly ignited by a jet flame. In contrast, Test B produces a horizontal jet flame with a maximum projection distance of 2.5 m, but the fire remains confined to the rear section. Additionally, the total heat release rate in Test A is about 1.71 times that of Test B. The study confirms that safety vent orientation significantly influences both fire spread behavior and combustion intensity in lithium-ion battery e-bike fires.

Key words: electric bicycle, lithium-ion battery, safety vent, combustion characteristics, fire risk