## 2 Materials and Methods
### Numerical Procedure
#### 2.2.3 Initial and Boundary Conditions  
In this numerical procedure, in addition to a geometric model of the equipment and piping system, the oil supply pipeline was set up near the typical high-temperature heated surface in the fishing vessel's engine room. The purpose was to simulate the ignition situation of marine oil leakage flowing to a heated surface when the oil supply pipeline is broken. This research focuses on the ignition process of leaked marine oil on a heated surface, as well as the influence of the interior environment of the fishing vessel's engine room. Marine diesel is a kind of mixed oil with complex fuel components. It was found that the cetane (C\({}_{16}\)H\({}_{34}\)) in the marine diesel occupies the highest proportion, and this component is an important index in measuring the ignition performance. The equipment housing in the diesel engine system forms a local high-temperature heated surface, which was set at a height of 1.0 m from the ground in the numerical model. In addition, the size of the heated surface in the fishing vessel's engine room was 0.5 m\(\times\)0.5 m. According to the measurement of the real environment in the fishing vessel's engine room, the initial environmental parameters are shown in Table 2 below.  
Since the environment of this numerical model is in a fishing vessel's engine room, the computational domain was divided into a fluid domain and a solid domain. The solid domain represents the mechanical equipment in the fishing vessel's engine room, and the surface of the main diesel engine equipment was set as a high-temperature heat transfer surface, that is, an initial fixed temperature was set. This simulation set different heated-surface temperatures ranging from 440 \({}^{\circ}\)C to 525 \({}^{\circ}\)C. The heated-surface temperature was set at an interval of 5 \({}^{\circ}\)C, for a total of 18 heated-surface temperature changes. According to the specific content involved in this research, the entrance of the fishing vessel's engine room was set as the velocity inlet, which is usually suitable for the flow of incompressible fluids. The parameters to be set include material velocity and volume ratio flowing into the computational domain through the inlet. They were used in this numerical model to set the ventilation velocity and humidity conditions. Based on the airflow organization in the engine room, four different wind speeds were: 0 m/s, 1.0 m/s, 3.0 m/s, and 5.0 m/s, respectively. The outlet boundary was set as a pressure outlet, and no additional pressure value was added at the outlet, that is, the normal pressure was set. In this numerical modeling, there were two types of walls in the physical model of engine room constructed. One type of wall is the heated surface, which was set to a fixed temperature and heat flux. The other type of wall is the equipment and engine room's wall, which was set as a fixed wall. For such walls, a fixed heat generator rate was set, which means how much heat is being added to the body from within. In order to further explore the influence of environmental humidity on the ignition process of leaked marine oil, three scenarios with different humidity conditions were set in the numerical model, with respective humidity values of 60%, 75%, and 85%. The data monitored during the simulation of the engine room model include the phase transition volume of the gas/liquid phase and the standard temperature of the fluid domain. The monitoring points were set up in different areas of the numerical model, especially in the area where the leaking marine oil heat meter ignition occurred. Thirty monitoring points were set up in the vertical space where the heated surface of the main diesel engine was formed, which is consistent with the experimental arrangement. Based on this, various results such as temperature data can be generated in the computational domain to meet the needs of this research.