## 3 Results and Discussion
### Effect of Humidity on Marine Oil Ignition in Engine Room  
In order to further explore the influence of environmental humidity in the fishing vessel's engine room on the ignition process of leaked marine oil, three scenarios with different humidity conditions were arranged, and the humidity values were set at 60%, 75%, and 85%. The humidity values correspond to different scenarios of a fishing vessel's port stay and sea operation. Figure 8 presents the variation in ignition height of the leaked marine oil on the heated surface under different humidity conditions in the fishing vessel's engine room. When the heated-surface temperature is the same, the ignition height of the leaking marine oil goes up with the increase in humidity. However, the magnitude of this change is not as significant as the effect of increased wind velocity on the ignition height. This indicates that the humidity in the air inhibits the upward transfer of heat; however, the degree of inhibition is limited. When the typical heated-surface temperature is 460 \({}^{\circ}\)C, the ignition height of marine oil at 60% humidity is approximately 0.481 m. If the humidity  
Figure 6: Heated-surface ignition occurrence of marine oil with different airflow velocities. Figure 7: Ignition delay time of marine oil with changed airflow velocities. in the engine room is moderately increased to 75%, the ignition height of the marine oil on the heated surface increases to 0.574 m, with an increase rate of 19.33%. If the humidity in the engine room is further increased, the ignition height of the leaking marine oil at this time goes up to 0.652 m. The numerical simulations have good agreement with the experimental results, and the CFD-based data are lower than the experimental data. When the typical heated-surface temperature of the fishing vessel's engine room rises to 475 \({}^{\circ}\)C, the ignition probability of the marine oil is close to 50%. At this heated-surface temperature, the ignition height of the leaked marine oil ranges from 0.401 m to 0.502 m, depending on humidity. Compared with the scenario where the hot-surface temperature is lower, the ignition position of the leaking marine oil is closer to the heated surface of machinery. With the further heating of the surface, the temperature reaches about 500 \({}^{\circ}\)C, and the marine oil above this temperature will achieve a fully ignited state. According to experimental data, under different humidity conditions, the ignition heights of the marine oil above the heated surface are 0.289 m, 0.335 m, and 0.413 m, respectively. The increase in the heated-surface temperature causes the marine oil leaking on the heated surface to evaporate rapidly, and the flammable vapor it forms quickly mixes with the air near the surface. The heated surface can provide a lot of heat within a short time, so the ignition behavior occurs in the area closer to surface. With the continuous increase in the surface temperature in the engine room, it is found that the ignition occurrence of the marine oil does not change greatly. Based on the fitting of comparative results, this research proposes a prediction model for the ignition occurrence of marine oil on a hot surface that is applicable to different humidity variation scenarios, with an R\({}^{2}\) of 0.926. As shown as Equation (20), the heated-surface ignition area can be determined when the marine oil leakage in the fishing vessel's engine room enhances the humidity condition. \[H=H_{0}+0.292\exp\left(-\frac{7T_{\mathrm{s}}}{5\pi\mathrm{g}}\right) \tag{20}\]  
The ignition delay time of marine oil is composed of liquid evaporation time and chemical reaction induction time. The difference in the ignition delay time represents the difference in the ignition characteristics of marine oils. Meanwhile, different characteristics of the ignition delay time of marine oils directly determine the protection focus in the fire process of a fishing vessel's engine room.