## 4 Results and Analysis
### Influence of Airflow on the Thermal Radiation from an EV Fire  
#### 4.1.1 Distribution of the Thermal Radiation Field from an EV Fire without Airflow  
(1) The thermal runaway combustion stage. When a thermal runaway fire occurs within the EV power battery and the flame spreads to the other parts of the vehicle, the energy of the battery is not completely released through the chain reaction of the thermal runaway. Therefore, we assumed that the PHRR of the thermal runaway combustion stage was 1/3 of the maximum energy storage capacity in the battery system. The simulation results are shown in Figures 6 and 7. It can be found that while in the thermal runaway fire stage, the safety distance for vertically parked vehicles was 2.3 m. The safety area for the pedestrians was 1.3 m in the positive direction of x\({}^{\prime}\) and 2.8 m in the positive direction of y\({}^{\prime}\) from the flame surface. (2) Vehicle combustion stage. The thermal radiation flux from the vehicle combustion stage, simulated under the boundary conditions of the scenario model, is shown in Figure 8. The closer the area was to the flame surface, the higher the incident thermal radiation flux. The safety distance of the fire propagation threshold was obtained through the distribution of the x\({}^{\prime}\)-y\({}^{\prime}\) coordinates and the distance between the adjacent vehicles was set as the safety distance for the fire propagation between the vehicles. According to the simulation results, the safety distance for the vertically parked vehicles was 4.5 m and the safety distance for the parallelly parked vehicles was 3 m.  
The results of the numerical calculation of the combustion thermal radiation from the EV based on the SFM are shown in Figures 9 and 10. The safety distance for the vertically parked vehicles was 3.4 m and the safety distance for the parallelly parked vehicles was 3 m.  
Figure 6: Distribution of the thermal radiation flux at the x = 2 m, x = 3 m and x = 4 m planes, in the thermal runaway combustion stage and without airflow. Figure 7: Distribution of the thermal radiation flux along the plane at different heights (1.7 m, 1.4 m and 1.1 m) in the pedestrian evacuation area, in the thermal runaway combustion stage and without airflow. To analyze the characteristics of the SFM as applied to the roadside parking fire scenarios, the radiation field was compared to that of the PSM. The point source was located at the geometric center of the vehicle head and the driver cabin flames, which was \((-1.125,\,-0.8345,\,1.27575)\) (unit: m) in the O\({}^{\prime}\)-x\({}^{\prime}\)-y\({}^{\prime}\) coordinate system. The thermal radiation for the PSM is given by, \(q=Q/12\pi R^{2}\), where q is the radiation flux at the target  
Figure 8: Distribution of the thermal radiation flux along the plane at different heights (1.7 m, 1.4 m and 1.1 m) in the vehicle combustion stage and without airflow. Figure 10: Distance curve of the thermal radiation flux at different heights (1.7 m, 1.4 m and 1.1 m), along the middle line of the front surface of the flame, in vehicle combustion stage and without airflow. Figure 9: Distribution of the thermal radiation flux along the plane at different heights (1.7 m, 1.4 m and 1.1 m) in the pedestrian evacuation area, in the vehicle combustion stage and without airflow. point, \(Q\) is the HRR of the fire source and \(R\) is the distance between the target and flame center points. The results of the numerical calculation of the combustion radiation from the EV based on the PSM are shown in Figure 11. The safety distance for the vertically parked vehicles was 1.4 m and the safety distance for the vehicles parked in parallel was 3 m.  
By comparing the three methods, the results of the safety distance are the same when the vehicles are parked in parallel, but there are some deviations in the safety distance when the vehicles are parked vertically.