Throughout current literature, different combinations between fuel cell type, heat engine type and fuel have been considered. Most studies focus on one combination, and operating conditions (fuel cell temperature, fuel cell pressure, cell voltage, fuel utilization factor, etc.) vary throughout these studies. Due to these variations in operating conditions, as well as differences in integration strategy, it is difficult to select a single combination to be the most suitable for marine applications. Additionally, current literature primarily focusses on maximizing system efficiency. Other factors such as system size, weight, IR signature and acoustic emissions are less frequently discussed in current literature. System size and weight are important factors for the feasibility of the combined cycles in current vessel designs, and the IR signature and acoustic emissions are important criteria for naval applications.

In this thesis, a solid oxide fuel cell (SOFC) is combined with an internal combustion engine (ICE) or a gas turbine (GT), and the system is fuelled by diesel or methanol (MeOH). This results in the following four combined cycles:
• Diesel-fuelled SOFC-ICE
• Diesel-fuelled SOFC-GT
• MeOH-fuelled SOFC-ICE
• MeOH-fuelled SOFC-GT
These combinations are compared for naval surface combatants based on system efficiency, annual energy consumption, annual CO2 emissions, exhaust gas temperature, total system weight and total system volume. Additionally, the combined cycles are compared to the current power generation system of a SIGMA surface combatant to determine the relative performance of the combined cycles to a conventional heat engine.

To determine the annual energy consumption, CO2 emissions and exhaust temperature, the combined cycles are modelled in Cycle-Tempo. The SOFC, ICE and GT are modelled as individual models and validated with available reference data. These individual models are then combined into a single model for each combined cycle, which is validated by comparing the results with results from current literature. The size and weight of the system is then obtained by selecting readily available components and summing their dimensions and weights.

For each comparison criteria, a different combined cycle performs the best. To minimize annual energy consumption, total system weight and total system volume, the diesel-fuelled SOFC-ICE combined cycle performs the best. To minimize exhaust gas temperature, the diesel-fuelled SOFC-GT combined cycle is the best choice. To minimize annual CO2 emissions, the MeOH-fuelled SOFC-ICE combined cycle is preferred. The exact performance of the combined cycles for these comparison criteria, depends on the power split between the SOFC and the heat engine. The annual energy consumption for the diesel-fuelled SOFC-ICE is between 4.4% (for a power split of 4.6-95.4) and 18.2% (for a power split of 25-75) lower than the current system of the SIGMA. The weight of this system is between 1.5% lighter (for a power split of 4.6-95.4) and 51.6% heavier (for a power split of 30-70) compared to the current system. For both the diesel-fuelled combined cycles, the exhaust temperature at silent speed can be reduced by 212 ◦C, which is a reduction of 58.3% compared to the current system. At cruising speed, the diesel-fuelled SOFC-GT can reduce the exhaust temperature with up to 207 ◦C at a power split of 30-70, which is a reduction of 65.8% compared to the current system. When using the MeOH-fuelled SOFC-ICE combined cycle, the annual CO2 emissions can be reduced by up to 25.9% compared to the current system for a power split of 25-75.

Depending on the preferred comparison criteria (annual energy consumption, emissions, exhaust temperature or system weight and volume), a different combined cycle and power split is preferred. There is no single solution that performs best for all criteria. It is therefore up to the designer to choose which criteria is most important and select the combined cycle accordingly. For this thesis, annual energy consumption and total system weight and volume are considered most important. For the combined cycles, a trade-off needs to be made between these criteria. A higher power split results generally in a lower annual energy consumption, but this also leads to a higher system weight and volume. To select the best power split for the SIGMA, a utopian solution is defined. This solution consists of the lowest annual energy consumption and the lowest system weight. This solution is impossible to reach, and the combined cycle and power split that lies closest to this utopian solution is deemed the best. This best solution is the diesel-fuelled SOFC-ICE combined cycle with a power split of 8.4-91.6 in favour of the ICE.

The diesel-fuelled SOFC-ICE combined cycle is implemented in the general arrangement plan of the SIGMA to assess the feasibility of this system in terms of system volume. The current power generation system (ICEs and diesel gensets) are removed, and the new components for the combined cycles are placed in the newly available space in the vessel. In the current general arrangement of the vessel, a maximum power split of 7.8-92.2 in favour of the ICE can be placed without having to change the design of the vessel. This power split is slightly lower than the ideal power split of 8.4-91.6. This lower power split results in a slightly higher annual
energy consumption and slightly lower system weight and volume compared to the ideal power split. Compared to the current system of the SIGMA, the diesel-fuelled SOFC-ICE combined cycle with a power split of 7.8-91.2 can reduce the annual energy consumption and CO2 emissions by about 6%. The exhaust temperature at silent speed reduces by about 212 ◦C (about 58%) and by about 80 ◦C (about 25%) at cruising speed. This reduction in energy consumption, CO2 emissions and exhaust temperature comes at the cost of a 4% increase in total system weight.

Overall, fuel cell combined cycles can help in reducing the fuel consumption and GHG emissions of the marine sector. Nevertheless, the implementation of fuel cell combined cycles alone is insufficient to reach the net-zero targets set by the IMO as outlined in [2]. For naval surface combatants, the combined cycles only reach a small reduction in fuel consumption and CO2 emissions (6%). The main benefit for these vessels lies in the reduction in exhaust gas temperature. A significant reduction in exhaust gas temperature (58% at silent speed and 25%
at cruising speed), and therefore a reduced IR-signature, is possible with a system small enough to still fit in the current design of the SIGMA.

The transition to sustainable propulsion in maritime transport has highlighted hydrogen-fueled PEM fuel cells as a compelling alternative to conventional diesel engines, driven by increasingly stringent emission regulations. While significant research has focused on single fuel cells or complete stacks, the hydrogen loop, the subsystem responsible for delivering, recirculating hydrogen, remains underexplored, particularly in the context of maritime applications. The hydrogen loop plays a critical role in determining system efficiency, reliability, and performance. Improper management of flow, pressure, temperature, and humidity can lead to lower efficiency, membrane dehydration, flooding, or even irreversible damage to the stack. To address this, a novel dynamic MATLAB Simulink model was developed to evaluate hydrogen loop configurations under realistic maritime conditions. This thesis investigates the design and performance of twelve distinct hydrogen loop configurations, each comprising different combinations of supply and recirculation components such as pressure regulators, proportional valves, mass flow controllers, liquid ring pumps, blowers, and ejectors. The configurations are motivated by real-world implementations from an inland vessel and a fuel cell-powered race car, as well as conceptual arrangements aimed at exploring broader designs. A novel, dynamic MATLAB Simulink model was developed that uniquely integrates pressure, temperature, humidity, twophase flow, and phase change dynamics, to capture both transient and steady-state behavior of hydrogen loops under realistic maritime conditions. Unlike existing models, it allows detailed componentlevel interaction analysis and configuration-specific scoring under a standardized testing framework. Key governing equations are based on established physics principles, and the model is validated using experimental data from the H2 Barge 1, an operational hydrogen-powered inland vessel from Future Proof Shipping. Each configuration is evaluated across a range of criteria, including hydrogen utilization, power consumption, performance, pressure and temperature robustness, stoichiometry control, and system response under transient loads. Special attention is given to component interactions that influence overall system behavior, such as the influence a recirculation device has on humidity and temperature, or the limitations of ejectors in low-load scenarios due to their dependency on primary flow pressure. Hybrid configurations combining ejectors with mechanical pumps are also explored to mitigate operational limitations at low power setpoints. The results highlight that hydrogen loop configuration choices have a significant impact on system performance, control flexibility, and design complexity. Ejector-based systems are energy-efficient and mechanically simple but suffer from limited operational range and lack dynamic control, especially at low loads. Mechanical recirculation devices like blowers and liquid ring pumps offer robust performance across the full load range and enable flexible operation, though they come with higher energy consumption and potential mechanical wear. Supply components also influence system behavior: proportional valves allow dynamic pressure control but require careful tuning, while mass flow controllers simplify control logic but lack pressure regulation. Hybrid solutions, combining ejectors with pumps, can mitigate some limitations but add complexity. Among the twelve configurations studied, the proportional valve–blower setup emerges as the most suitable for maritime fuel cell applications, offering the best balance of efficiency, operational flexibility, robustness, and system simplicity. Ultimately, this research provides a structured methodology for comparing hydrogen loop configurations, enabling system designers to make informed decisions based on specific performance requirements and operational constraints. The findings underscore the importance of integrated system modeling in BoP design and contribute to the broader goal of developing scalable, reliable, and efficient hydrogen propulsion systems for maritime applications.

Ships play a crucial role in global transportation, yet they significantly contribute to greenhouse gas emissions. The International Maritime Organization targets net-zero emissions by 2050, necessitating cleaner energy solutions. Solid oxide fuel cells (SOFCs) offer higher efficiency than diesel engines, reducing carbon emissions and toxic pollutants. This dissertation explores the integration of SOFC systems into ships, assessing fuel options, efficiency, and operational challenges. Experimental studies examine SOFC performance under ship motions, highlighting the need for design adaptations. Thermodynamic analysis compares various fuels, identifying methane and ammonia as optimal choices based on efficiency and heat demand. A megawatt-scale SOFC system is conceptually designed to enhance power density. Hybrid power plant simulations demonstrate significant emission reductions, especially for auxiliary loads. The study concludes that SOFCs are viable for multiple ship types, particularly those with stable load profiles. Further advancements in alternative fuels and system design are essential for widespread adoption.

Carbon corrosion occurring on the cathode of a polymer electrolyte membrane fuel cell (PEMFC) leads to a reduction in the electrochemical surface area (ECSA). The ECSA is crucial for the efficiency and maximum power output of the fuel cell. Degradation of this component is detrimental to the overall performance of the system. Research into the mechanisms of ECSA degradation is essential for understanding and preventing fuel cell deterioration. The carbon in the electrode functions as a support material for the catalyst and provides the necessary electrical conductivity. Carbon corrosion can increase resistance between the electrode and the catalyst, and research suggests it may even cause the catalyst to detach from the electrode. This thesis investigates carbon dioxide emissions from a PEMFC during an accelerated stress test (AST), measured using a gas analyzer. The exhaust gases contain
approximately 600 parts per million (ppm) of carbon dioxide, fluctuating by about 100 ppm throughout the day. A fluctuation of 80 ppm, attributed to changes in oxygen content during the operational and shutdown phases of the PEMFC stress cycle, was also identified. A formula was applied to remove these fluctuations to better understand the emissions. Carbon dioxide emissions were detected during the startup phase, when a hydrogen-air front is active at the anode, making carbon corrosion at the cathode likely. The area under the emission peak was determined and multiplied by the flow rate, providing an estimate of the carbon dioxide emissions and the corresponding carbon mass loss from the cathode. A secondary objective of this thesis was to validate a mathematical model of carbon corrosion with the obtained data. However, this was not possible with the current data set. The model does
not account for the dynamic conditions of the stress test, which are typically significant contributors to carbon corrosion in a PEMFC.