## 3 Results and Discussion
### Effect of Ventilation on Marine Oil Ignition in Engine Room  
The mechanical ventilation equipment will be turned on during the daily operation of a fishing vessel's engine room, and the ventilation volume will be adjusted according to different operation scenarios. This section focuses on the differences in wind velocity in the engine room under different ventilation rates and the change in the ignition process of leaking marine oil. According to airflow organization in the fishing vessel's engine room, four types of wind velocity in the engine room were set in this research: 0 m/s, 1.0 m/s, 3.0 m/s, and 5.0 m/s. The change in airflow organization in the engine room is directly reflected in the change in ignition characteristics of leaked marine oil. Figure 6 shows the variation in ignition height of leaked marine oil under different wind velocities in the engine room. The solid points in Figure 6 represent experimental data, and the hollow points represent numerical simulation data. On the whole, it can be seen that in the scenario of the same wind velocity, the ignition height of the marine oil on the heated surface shows a downward trend with the increase in the heated-surface temperature. This indicates that the increase in the heated-surface temperature causes the marine oil above the heated surface to evaporate rapidly, and the flammable vapor it forms quickly mixes with the air near the surface. Due to the high temperature of the surface itself, it can provide a lot of heat in a short time, so the ignition occurs in the area closer to the heated surface. As the heated-surface temperature continues to rise, it is found that the ignition height of the marine oil will no longer fluctuate greatly, but basically maintain in the area of 0.29 m to 0.51 m above the heated surface. According to the experimental data, there is a fitting relationship between the ignition height of the marine oil and the heated-surface temperature, as shown in Equation (19). The correlation coefficient R\({}^{2}\) of the present model reaches 0.944. The fitting relationship can be used to determine the initial ignition location of marine diesel at different heated-surface temperatures. In the scenario where the typical heated-surface temperature of a fishing vessel's engine room is consistent, the ignition height of leaked marine oil increases with the wind condition strength in the engine room. The mechanical ventilation in the engine room enhances, which restricts the ignition process of the marine oil on the heated surface to a certain extent. Since the air supply and exhaust system in fishing vessel's engine room supply air at the bottom and exhaust air at the top, more marine oil vapor is carried higher by the airflow movement. Under enhanced ventilation conditions, marine oil vapor forms a volume fraction with ignition conditions at a higher position above the heated surface. Once the ignition occurs,  
Figure 5: Ignition probabilities of leaked marine oil with growing heated-surface temperatures. the location of the ignition occurrence is far from the heated surface, which is significantly different from the accident scenario without mechanical ventilation. \[H=H_{0}+0.149\exp\left(-\frac{T_{\mathrm{s}}}{\pi\mathrm{g}}\right) \tag{19}\]  
where \(H\) is the height of marine oil ignition occurrence on the heated surface, m; \(H_{0}\) is the surface height of the marine oil, m; \(T_{\mathrm{s}}\) is the heated-surface temperature in the engine room, K; and g is the gravity acceleration, m/s\({}^{2}\). The ignition delay time of marine oil is of great significance in characterizing its accidental ignition characteristics. The ignition delay time refers to the time required for the system of the combustible vapor mixture to reach an ignition condition, from the initial temperature rise to the initial ignition phenomenon. Different marine oils show different ignition characteristics on high-temperature heated surfaces, and the time required for ignition is varied.