## 3 Results and Discussion
### Effect of Ventilation on Marine Oil Ignition in Engine Room
The leakage of diesel on a heated surface and the occurrence of local ignition are two basic necessary premises. The first is that there is a suitable mixture ratio of vapor/air in the ignition area, which can promote the formation of an initial flame. On the other hand, environmental factors in the fishing vessel's engine room are important. After the initial flame is formed, such a flame can stabilize itself in the region where it occurs at a low-velocity flow field. Then, through flame transmission, it can achieve stable propagation to an unburned gaseous mixture in space. There are complex influencing factors in the fishing vessel's engine room that are different from the time required for the initial ignition of marine oil in other scenarios. The experimental tests and numerical simulations of the relationship between the ignition time of leaked marine oil and heated-surface temperature were carried out under different wind velocity conditions. Through the combination of experimental and numerical results, this research explores the change rule of time required for marine oil ignition above the heated surface under different engine room wind velocities. Figure 7 shows the change in the ignition delay time of leaked marine oil with heated-surface temperatures in different engine room wind velocity scenarios. The ignition delay time represents the time required for the initial ignition of a vapor/air mixture on the heated surface, which directly determines the risk degree of the engine room fire accident. It can be seen from the Figure 7 that under the same wind condition, the ignition delay time of the leaked marine oil on the heated surface shows a downward trend with increasing heated-surface temperature. This is because the vapor/air mixture is acted upon by the increasing heated-surface temperature, which undergoes a violent chemical reaction in the region closer to thermal boundary. This violent chemical reaction take place precisely because the combustible gaseous mixture is heated to a certain temperature by the surrounding heat source, and such a heat release is greater than the heat release to the surrounding environment. It ultimately leads to the automatic acceleration of the chemical reaction, forming the initial flame. Meanwhile, Figure 7 indicates that at the same heated-surface temperature, the enhanced engine room's wind velocity results in a longer ignition delay time for the leaked marine oil. Due to the increase in the amount of ventilation in the fishing vessel's engine room, the wind velocity increases, which causes the air distribution in the area around the heated surface to change. This change causes the marine oil vapor to form a concentration higher than the heated surface, so the time required for the ignition of the vapor/air mixture increases. It brings about new fire accident risks in the fishing vessel's engine room. When the ventilation condition in the engine room is enhanced, the ignition time after the leaked marine oil contacts the heated surface will be prolonged, and it is more necessary to strengthen the monitoring and control measures of the area where ignition may occur.