## 3 Results and Discussion
### Evaporation Mechanism of Marine Oil Ignition by Heated Surface
The liquid phase volume of the marine oil was monitored, and its change is shown in Figure 3b. The movement of the liquid molecular flow of the marine oil on the heated surface of the engine room exists from the beginning and synchronizes with the gas phase change of the marine oil. Figure 3b shows the location of initial marine oil accumulation, and the thickness and accumulation range of the marine oil above the heated surface can be observed from the image. After the leaked marine oil is affected by the heated surface of the fishing vessel's engine room, it gradually begins to flow to two sides. The two sides are more symmetrical, and the whole flow displays a horn shape. According to the numerical simulations, a small number of liquid phase molecules of the marine oil appear in the left air in the engine room, and their shape is basically similar to the marine oil vapor formation profile. In the space above the heated surface, the spot liquid phase molecules of the marine oil gradually increase. Subsequently, the liquid phase molecules in the air begin to disappear, and the leakage marine oil at the bottom shows a normal flow and fluctuation state. The liquid phase molecules located on the heated surface show a normal flow state, and the gas phase molecules in the environment of the engine room gradually increase. The change in the liquid phase medium after the oil leakage is heated on the heated surface shows that the liquid phase movement presents a symmetrical change at the initial stage. Subsequently, the leaked marine oil begins to flow slowly to both sides of the high-temperature heated surface, and the flow state is completely unconstrained. It can be seen from the phase diagram of the marine oil that there are some small fluctuations on the marine oil surface. Due to the small-diameter range of the marine oil accumulation areas, some of marine oil begins to flow to the areas in direct contact with the heated surface. At this time, the leaked marine oil layer at the heated surface is relatively thin. With the continuous flow of leaking marine oil, the thickness of the oil layer at the edge gradually increases. Meanwhile, the thickness of the oil layer in the middle decreases, and the marine oil reaches a pseudo-dynamic equilibrium state on the whole. When the marine oil is subjected to high-temperature heated-surface action to reach its saturation temperature, molecules overflow from the liquid to become vapor. In the environment of the fishing vessel's engine room, it begins to diffuse, and a part of the oil vapor re-forms a liquid state after collision, but it does not completely fall onto the heated surface. There are a large number of liquid phase molecules in the air. The number of molecules that re-form the liquid phase is much smaller than that of molecules evaporating into the gas phase after being acted on by the heated surface, which has a strong promotion effect on ignition. Heated gaseous molecules of marine oil are transferred in two ways: the transport of components caused by the macroscopic overall flow of the fluid, or molecular diffusion, which includes the conventional diffusion motion from a region of high concentration to a region of low concentration and thermal diffusion caused by a temperature gradient, as shown in Equation (15). \[\dot{\mathrm{m}}_{\mathrm{A}}^{{}^{\prime\prime}}=Y_{\mathrm{A}}\big{(}\dot{ \mathrm{m}}_{\mathrm{A}}^{{}^{\prime\prime}}+\dot{\mathrm{m}}_{\mathrm{B}}^{{} ^{\prime\prime}}\big{)}-\varrho D_{\mathrm{AB}}\frac{\mathrm{d}Y_{\mathrm{A}} }{\mathrm{d}_{\mathrm{x}}} \tag{15}\]  
where \(\dot{\mathrm{m}}_{\mathrm{A}}^{{}^{\prime\prime}}\) is the mass flux of component A per unit area, kg/(s\(\cdot\)m\({}^{2}\)); \(Y_{\mathrm{A}}\) is the mass fraction; and \(D_{\mathrm{AB}}\) is the diffusion coefficient, m\({}^{2}\)/s. Figure 3c,d show the process of evaporation and phase change of the leaked marine oil on the heated surface after mechanical ventilation, respectively.