# Analysis of Internal Gas Leaks in an MCFC System Package for an LNG-Fueled Ship
## 1 Introduction  
The policies for marine environmental regulations of the International Maritime Organization (IMO) and governments have recently been strengthened to reduce air contaminants and greenhouse gases, including nitrogen oxides (NO\({}_{\mathrm{x}}\)), sulfuric oxides (SO\({}_{\mathrm{x}}\)), and carbon dioxide (CO\({}_{2}\)). Marine engineers have therefore considered various strategies for building green ships such as developing a highly efficient propeller, modification of fan shapes, and optimization of an operational window [1; 2; 3]. In particular, in 2016, the IMO Marine Environment Protection Committee (MEPC) restricted the emissions of SO\({}_{\mathrm{x}}\) from 3.5% to 0.5% for marine ships in the entire ocean until 2020 [4]. Today, many shipping firms are adopting liquefied natural gas (LNG) as marine fuel in an attempt to replace conventionally used heavy fuel oil (HFO). The use of LNG in ships is considered to be a way to safely use boil-off gas (BOG) that is naturally generated by heat leaks. As one option, the application of fuel cells to ships is being considered [5]. However, the ultimate goal of shipbuilders is to replace diesel engines, which emit greenhouse gases, with regenerative energy generators (zero-emission ships). Energy storage systems (ESSs), and sunlight have received significant attention as environmentally friendly energy sources for green ships in the future [6]. Among these, fuel cells (FCs) have strong potential as an alternative to traditional marine propulsion power plants owing to their high efficiency,easy modularization, multi-fuel flexibility, and environmental friendliness [7]. In addition, FCs can essentially offer a silent and vibration-free operation, reducing the need for noise insulation of machinery. In particular, high-temperature molten carbonate fuel cells (MCFCs) have various advantages for green ships, because they achieve a system efficiency of more than 80%, with negligible air-pollutant emissions when the waste heat is recovered. Furthermore, it may be economically efficient to use fuels such as LNG and liquefied hydrogen (H\({}_{2}\)) carriers in gas-fueled and gas carriers, because MCFCs can use the BOG emitted from the LNG ship [8; 9]. However, the development of green ships using fuel cells is still at a primitive stage, because of the considerable cost and time needed for construction of ships. Furthermore, liquefied gas carriers and gas-fueled ships may pose a high risk of explosion and fire from gas leaks, resulting from the localized damage (thermal expansion) of system components caused by high heat, because MCFCs are operated at a high temperature [10]. In addition, in order to use fuel cells in gas-fueled and gas carriers, severe weather and sea winds are considered among the design parameters needed to build a highly stable green ship with fuel cells. In this regard, mathematical modeling plays an important role by significantly reducing the need for repetitive experiments and confirming concepts for building ships [11; 12; 13]. Moreover, several technical issues associated with the high operating temperature, such as explosion and fire caused by high heat, can be explored and thus mitigated through the new design and development progress for MCFC green ships. [PERSON] and [PERSON] (2012) [14] first reported the modeling work for an MCFC auxiliary power unit installed on board a vessel. They developed a modular dynamic model consisting of a set of partial differential and non-linear algebraic equations, employing 2D and 3D solid geometry and real gas properties to provide insight into the process dynamics and cell performance. [PERSON] et al. [15] also presented the modeling approach as a tool for improving the current collector and gas distributor designs, optimizing MCFC performance with new technological solutions. This approach played a fundamental role in the thermal management of the MCFC, which is one of the most crucial points in performance improvements.