## 3 Results and Discussion  
### Evaporation Mechanism of Marine Oil Ignition by Heated Surface  
The liquid phase change of marine oil leakage on a heated surface of a fishing vessel's engine room is directly related to the formation of a gas phase, so it is necessary to observe the liquid phase flow and change process of marine oil leakage. Figure 3 shows the image data collected during the experiment and numerical simulation. Figure 3 presents the evaporation process of leaked marine oil on a heated surface when there is no mechanical ventilation in the engine room. It is found that when marine oil is leaked on a heated surface, its phase state changes rapidly. The temperature of a typical heated surface inside the engine room is higher than the initial temperature of the marine oil. When the temperature difference between the typical heated surface and the leaked marine oil is less than 278 K, the solid-liquid interface is in a state of natural convection. Normally, the temperature of a typical heated surface of fishing vessel's engine room is higher, which causes different forms of boiling when marine oil comes into contact with it. When the temperature difference between the heated surface and leaking marine oil reaches 278 K to 308 K, nucleate boiling occurs in the solid-liquid interface. If the typical heated-surface \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & \begin{tabular}{c} **Internal** \\ **Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} & \begin{tabular}{c} **External** \\ **Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} & \begin{tabular}{c} **Relative** \\ **Humidity** \\ **(\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Internal** \\ **Airflow** \\ **Velocity** \\ **(m/s)** \\ \end{tabular} &
\begin{tabular}{c} **Atmospheric** \\ **Pressure** \\ **(MPa)** \\ \end{tabular} \\ \hline Value & 45 & 32 & 60 & 1.0 & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Environmental parameters of engine room in fishing vessel. temperature of a fishing vessel's engine room continues to rise, and the difference between it and temperature of the marine oil is greater than 308 K, it will enter a state of transition boiling. This state is between nuclear boiling and film boiling, and the heated-surface temperature at this time is higher than that of nuclear boiling. According to detection of the equipment surface in the engine room, it is found that the heated-surface temperature formed by the high-speed operation of mechanical equipment is usually several times or even ten times the temperature in the engine room. In the case of higher heated-surface temperatures of the fishing vessel's engine room, the temperature difference between the heated surface and marine oil is larger. In this scenario, leaked marine oil will boil violently on the heated surface, and a vapor film will form on the oil surface. This state is called film boiling, which occurs at temperatures above the transition boiling condition. The formation of a gas phase layer between the marine oil and heated surface can be clearly observed from the image collected by the high-speed camera, and the formation time is very short. When film boiling occurs on the heated surface, the flammable vapor produces a different distance from the leaked marine oil surface. Since there is no mechanical ventilation in the engine room, the vapor flow of the leaking marine oil on the heated surface is slower. White vapor is produced by the heating of marine oil, and it accumulates above the heated surface. After the marine oil vapor is fully mixed with the surrounding air of the engine room, a combustible mixed vapor cloud is formed that has a clear cloud profile, as shown in Figure 3a. Figure 3: Evaporation process of leaked marine oil on heated surface: (**a**) experimental record without mechanical ventilation; (**b**) numerical simulation without mechanical ventilation; (**c**) experimental record under airflow in ship engine room; (**d**) numerical simulation under airflow in ship engine room.