## 1 Introduction
In ship fire accidents, the risk of the main engine fuel system is the highest, because the leakage of marine fuel from the piping system or diesel supply tanks is the main failure cause [11]. [PERSON] et al. [12] applied a Bayesian Network (BN) method to analyze the probabilities of ship fires, and this work revealed the symptoms of poorly conditioned vehicles, including aging electrical lines and heavy oil stains in the ship engine room. The leakage of marine fuel, which may be ignited by a heated surface, is the main contributor to ship engine room fires. [PERSON] et al. [13] conducted an assessment of specific risk-influencing factors regarding the occurrence of ship accidents based on a global sample involving 936 events from the period of 2005-2017. Fires, collisions, and groundings represented nearly 50% of the overall number of ship accidents. Some other dynamic risk assessments of different types of ships were carried out, illustrating the common problems of piping failures and potential ignition sources from the machinery system in the engine room [14; 15; 16; 17]. In fact, an accidental release of marine fuel can lead to a stratified vapor cloud in the ship engine room. Two kinds of hazards can take place: one referring to mechanical damage caused by overpressure resulting from an explosion, and the other concerning heat exposure from fire development [18]. Therefore, it is of great value to understand the safety management of small fishing ships [19], including the piping system design and environmental conditions related to engine operations. Many previous numerical studies have been conducted on ship fires. For example, [PERSON] et al. [20; 21] completed ship engine room fire simulations by using large eddy simulation (LES). The numerical models were performed in a fire dynamics simulator (FDS), and the main engines and auxiliary machines were constructed in an engine room. The simulated results indicated that the temperature distribution in the ship engine room is significantly different, and the negative pressure would have an effect on ship fire development. [PERSON] et al. [22] focused on how to arrange ship fire control with minimal changes to existing design, and their study showed a framework for using a numerical method in the initial stage of ship fire safety. Meanwhile, it is also important to effectively estimate the risk index and the possibility of fires in real time. [PERSON] et al. [23] developed a prediction model by using ANASYS CEX and PHAST data [24] that can evaluate the consequences of ship engine room fires at the beginning stage. [PERSON] et al. [25] reconstructed a 3D model of a ship engine room based on the distant-water training ship Yukun in Dalian, China. They found that a flame would appear in a mechanically ventilated engine room. The flame propagation was subject to a comparative effect from the momentum, buoyancy, and pressure of the ship engine room's airflow. The arrangement of ventilation conditions in the ship engine room has a great effect on flammable material ignition and flame propagation, which affects the combustion characteristics in ship fire accidents [26]. Numerical models for ship fires were built by CFD-based tools based on standards and cases [27; 28], which showed better improvements by combating with experimental data [29; 30]. In another experiment, it was found that the general behavior of marine oils was steady combustion after ignition in open space, where the low and intermediate fractions began to evaporate, causing a large number of bubbles [31]. [PERSON] et al. [32] carried out a series of tests in a sealed ship engine room, and the experimental results indicated that the evaporated fuel was not involved in chemical reactions during the burning process, resulting in a burning rate of marine fuel lower than the mass loss rate. [PERSON]'s experimental work [33] found a new flame spreading phenomenon of \"continuous-flow around-broken-retract\" in ship fires.