## 3 Results and Discussion
### Evaporation Mechanism of Marine Oil Ignition by Heated Surface
Figure 3c is the screen collected in the experiment, and Figure 3d is the cloud image generated by the numerical simulation. With the change in time, there are two distinct periods of growth of the marine oil evaporation. In the earlier period, the evaporation of the leaked marine oil in the engine room under low wind velocity conditions is higher than the change value under high wind velocity conditions. The analysis indicates that the influence of mechanical ventilation on the engine room environment increases after the mechanical ventilation is increased. This results in heat loss from the heated surface of the equipment and is not conducive to the endothermic evaporation process of the marine oil. Therefore, the marine oil ignition time will be shortened under low wind velocity in the engine room. When the  
inflection of marine oil evaporation is reached, the evaporation amount of marine oil will jump obviously. It is believed that this is due to the transition from natural evaporation to boiling evaporation. The marine oil in the fishing vessel's engine room is transferred by the heated surface and begins to spread into the engine room environment after reaching the vaporization temperature. At this time, the ventilation in the engine room takes away the oil vapor phase medium above the heated surface, thus promoting the transformation of the liquid phase of the marine oil into the gas phase, and finally the evaporation amount of the marine oil above the heated surface increases with the strength of the wind force in the engine room. The evaporation rate of the marine oil leakage decreases gradually in the later period because the marine oil vapor gathers above the liquid phase surface, and the decrease in the concentration difference leads to a decrease in the rate. With the weakening of the mechanical ventilation in the fishing vessel, the smaller relevant ventilation volume takes away less oil vapor above the surface of the liquid phase, and the marine oil evaporation rate decreases accordingly. The results of the experiment and numerical simulation show high agreement. Figure 4 shows the process in which marine diesel oil leaks to the heated surface, forming an initial ignition and causing flame propagation. Figure 4a presents the initial ignition of leaked marine oil when the heated-surface temperature reaches 460 \({}^{\circ}\)C. Figure 4b shows the initial ignition of leaked marine oil when the heated-surface temperature rises to 500 \({}^{\circ}\)C. When the typical heated-surface temperature of the engine room changes, there is a significant difference in the hot-surface ignition position of the marine oil. Marine diesel oil is a multi-component mixture: it is composed of C\({}_{12}\)\(\sim\)C\({}_{23}\) alkanes and contains aromatic hydrocarbons and a small amount of organic sulfur, nitrogen oxides, and other substances. Once marine diesel oil is in contact with a high-temperature surface, it produces a large amount of white flue gas mixture in a short time. Related to the flow characteristics of marine diesel, the combustible gas mixture formed on the heated surface of marine diesel has a wide range. The evaporation products produced by marine diesel oil on a heated surface can be fully mixed with the air in a fishing vessel's engine room. The mixed medium can form stable combustible mixed clouds in the vertical space above the heated surface. At this time, there is continuous heat transfer from the heated surface to the liquid surface, coupled with the thermal feedback effect around the engine room. As shown in Figure 4a,b, when marine diesel oil leaks for a certain period of time, the mixed vapor cloud experiences an instantaneous initial ignition above the heated surface. This instantaneous ignition phenomenon is difficult to directly observe and can only be captured through high-speed photography technology to collect the instantaneous impact, showing the occurrence location of the ignition.