Hydrogen carriers are attractive alternative fuels for the shipping sector. They are zero-emission, have high energy densities, and are safe, available, and easy to handle. Sodium borohydride, potassium borohydride, dibenzyltoluene, n-ethylcarbazole, and ammoniaborane are hydrogen carriers with high theoretical energy densities. The energy density is paramount to implementing hydrogen carriers as a high energy density enables compact and lightweight storage. The effective energy density depends on integrating heat and masses with energy converters. This combination defines the energy efficiency and, thus, the energy density of the system. This paper addresses the effective energy density of the hydrogen carriers, including the dehydrogenation process. Using a 0D model, we combined the five carriers with two types of fuel cells, namely proton exchange membrane (PEM) and solid oxide fuel cells (SOFC), an internal combustion engine and a gas turbine. N-ethylcarbazole and dibenzyltoluene offer medium energy densities, reaching almost 4 MJ/kg. However, the effective energy density of sodium borohydride and ammoniaborane is very high, up to 15 MJ/kg, including the energy converter. This is similar to the energy density of marine diesel oil combined with an internal combustion engine. Thus, we conclude hydrogen carriers are alternative fuels that deserve more attention because of their strong potential to make shipping zero-emission.

The inland waterway transport sector is facing increasingly stringent legislation to reduce emissions and improve energy efficiency. Speed planning has the potential to provide logistically compliant, energy-efficient, and emission-reducing voyages for inland vessels. However, current speed planning methods do not consider PM and NO_x emissions, nor do they consider alternative power systems to internal combustion engines (ICE) and full electric systems. These omissions have led to a lack of clarity on the impact of speed planning on the emission profile of inland vessels and the impact of alternative power systems on energy consumption. In this paper we propose a validated speed planning method that considers the emission profile (CO₂, PM₁₀, and NO_x) and different engine types for inland vessels in an leg-based speed planning approach while taking into account varying fairway water depth and speed. Through a use case we show that the vessel can achieve a 7.26% energy, 5.37% CO₂ and fuel, 3.85% NO_x, and 6.77% PM₁₀ reduction while maintaining the same arrival time; showing a distinct difference of this method compared to slow steaming. We also find that CO₂, NO_x, PM₁₀, and energy are not directly proportional when making speed adjustments. Finally, we analyze the adverse effects of emission control areas and emission limits on the energy consumption and arrival times of vessels with non-zero emissions propulsion.

Solid oxide fuel cell systems are considered for the power plant of ships, because of their high efficiency, low pollutant emissions, and fuel flexibility. This research compares the volume, mass, fuel consumption, and emissions of different hybrid power plants for cruise ships using solid oxide fuel cells, fuelled with marine gas oil and liquefied natural gas. A component sizing model allocates the installed power over the selected power plant components and determines their size and weight. The components and energy management strategy are simulated with a cruise ship for five years of operation. A simple method is implemented to estimate the degradation and its effect on component operation. The combined component sizing and time-domain model highlights the importance of dynamic simulation for battery sizing. The results show that using solid oxide fuel cells for the auxiliary consumers can reduce greenhouse gas emissions by 21% and pollutants by 38% to 46% with only 17.5% installed power, which has limited consequences for the cost and size of the power plant. With 31% installed power, the ship can operate in low-emission zones while reducing greenhouse gas emissions by 33% and pollutants by 60% to 70%. Performing all cruise operations requires 51% installed fuel cell power and reduces greenhouse gas emissions by 49% and pollutants by 94% to 96%. In conclusion, the study affirms that solid oxide fuel cell systems, with proper sizing and energy management, can be used to reduce shipping emissions and reach IMO's 30% GHG emission reduction target for 2030.

– Hydrogen carriers, such as liquid organic hydrogen carriers (LOHCs) and borohydrides, are promising zero-emission alternative fuels for ships. Bringing these hydrogen carriers on board, however, creates new challenges. A major challenge is their spill behaviour. Knowing the spill behaviour is paramount to avoid large-scale environmental disasters. This paper investigates the spill behaviour of four hydrogen carriers (and their conjugates): sodium borohydride, ammonia borane, dibenzyltoluene, and n-ethylcarbazole. The hydrogen carriers were all dissolved in artificial seawater to test their behaviour. Sodium borohydride reacts with seawater, as it also reacts with pure water. However, contrary to expectations, it reacts faster with seawater than regular water. The reaction mechanism behind this is unknown. Ammonia borane does not visibly react with normal water or with seawater. Dibenzyltoluene sinks and forms tiny bubbles which are easily perturbed. Unfortunately, perhydro dibenzyltoluene could not be tested due to technical problems. N-ethylcarbazole breaks up into smaller pieces and predominantly stays afloat, likely due to the surface tension of water. Perhydro n-ethylcarbazole floats but is barely visible in seawater due to its transparency. Preventive measures must be established to avoid large-scale spills if these substances are utilised on ships, as they are likely challenging to clean up.

Green hydrogen combined with PEM fuel cell systems is a viable option to meet the demand for alternative maritime fuels. However, hydrogen storage faces challenges, including low volumetric density, fire and explosion risks and transport challenges. We assessed over fifteen hydrogen carriers based on their maritime performance characteristics to determine their suitability for shipboard use. Evaluation criteria included energy density, locally zero-emission, circularity of process, safety, dehydrogenation process, logistic availability and handling. Thus, excluding ammonia and methanol because of these constraints, we found that borohydrides, liquid organic hydrogen carriers and ammoniaborane are the most promising hydrogen carriers to use on ships with PEM fuel cells. Borohydrides, specifically sodium borohydride, have high energy densities but face regeneration issues. The liquid organic hydrogen carrier dibenzyltoluene has a lower energy density but exhibits easy hydrogenation and good handling. Given varying operational demands, we developed a framework to assess the suitability of hydrogen carriers for use in different ship categories. Evaluating the three types of hydrogen carriers, using our framework and considering current practices, shows that these are viable options for almost all ship types. Thus, we have identified three types of hydrogen carriers, which should be the focus of future research.

Solid Oxide Fuel Cell (SOFC) systems have the potential to reduce emissions from seagoing vessels. However, it is unknown whether ship motions influence the system's operation. In this research, a 1.5 kW SOFC module is operated on an inclination platform that emulates ship motions, to evaluate the influence of static and dynamic inclinations on the system's safety, operation, and lifetime. The test campaign consists of a static inclination test, a dynamic test, a degradation test, and a high acceleration test. There were no interruptions in the power supply during the different tests, and no detectable gas leakages or safety hazards. Although the SOFC does not fail in any test condition, dynamic inclinations result in forced oscillations in the fuel regulation, which propagate through the system by different feedback loops in the control architecture, leading to significant deviations in the operational parameters of the system. Additionally, for motion periods from 16 to 26 s, reoccurring exceedance of the fuel utilisation results in a gradual reduction of the power supply. Several enhancements are recommended to improve the design of SOFCs and marine fuel cell regulations to ensure their safe operation on ships.

An increasing demand in the marine industry to reduce emissions led to investigations into more efficient power conversion using fuels with sustainable production pathways. Solid Oxide Fuel Cells (SOFCs) are under consideration for long-range shipping, because of its high efficiency, low pollutant emissions, and fuel flexibility. SOFC systems also have great potential to cater for the heat demand in ships, but the heat integration is not often considered when assessing its feasibility. This study evaluates the electrical and heat efficiency of a 100 kW SOFC system for marine applications fuelled with methane, methanol, diesel, ammonia, or hydrogen. In addition, cathode off-gas recirculation (COGR) is investigated to tackle low oxygen utilisation and thus improve heat regeneration. The software Cycle Tempo is used to simulate the power plant, which uses a 1D model for the SOFCs. At nominal conditions, the highest net electrical efficiency (LHV) was found for methane (58.1%), followed by diesel (57.6%), and ammonia (55.1%). The highest heat efficiency was found for ammonia (27.4%), followed by hydrogen (25.6%). COGR resulted in similar electrical efficiencies, but increased the heat efficiency by 11.9% to 105.0% for the different fuels. The model was verified with a sensitivity analysis and validated by comparison with similar studies. It is concluded that COGR is a promising method to increase the heat efficiency of marine SOFC systems.

This paper introduces a machine learning approach for optimizing propellers. The method aims to improve the computational cost of optimization by reducing the number of evaluations required to find solutions. This is achieved by directing the search towards design clusters with good performance, i.e. high propulsive efficiency and low cavitation. Three types of clusters are expected. The first cluster constitutes designs with performance of interest, i.e. high efficiency and low cavitation. The second cluster constitutes designs with performance not of interest, i.e. low efficiency and high cavitation. The third cluster constitutes designs whose performance cannot be estimated with the Boundary Element Methods (BEM) that we use in this study. In simple cases with single objective optimization to maximize efficiency, these clusters can be identified a-priori with unsupervised classifiers provided that orthogonally independent parameters are used as demonstrated in this paper. For multi-objective constrained optimization, to maximize efficiency and minimize cavitation, for example, supervised classifiers may be required to learn the clusters. Classical design variables such as chordlength, pitch, skew, rake, thickness distribution and camber of hydrofoils cannot be used to identify these clusters because of multicollinearity. Thus, a new orthogonal parametric model is proposed where the parameters are directly derived from the propeller blade mesh. As the blade surface mesh is used as boundary conditions to solve the governing equations, the orthogonal parameters are expected to have a stronger correlation with performance predictions of BEM or Computational Fluid Dynamics (CFD) than classical design variables. We demonstrate that design clusters with good performance can be identified with few BEM evaluations. Furthermore, the method synergizes explainable supervised and unsupervised learning to advice search algorithms and quickly guide them to lucrative regions in the design space. However, reducing the cost of optimization results in a trade-off with completeness of the search; this is also investigated in this paper. The method is demonstrated on a simple fully wetted flow case of the benchmark Wageningen B-4 70 propeller with P/D=1.0, as the geometry and open-water curves are readily accessible allowing back of the envelope verification and validation of our results.

Analysis of ship propulsion system performance is often performed using detailed hydrodynamic models to assess load changes, which are subsequently compared to static engine limits, or by detailed engine models that are rarely integrated with sufficiently detailed propulsion models for load change estimation. To investigate the dynamic engine (overloading) behaviour and ship propulsion performance under various heavy operating conditions, a Mean Value First Principle Parametric (MVFPP) engine model is integrated into a ship propulsion system model in this paper. An upgraded thermodynamic-based MVFPP model for two-stroke marine diesel engines is presented, in particular a newly developed MVFPP gas exchange model. Based on the integrated propulsion system model of a benchmark ocean-going chemical tanker, the engine dynamic behaviour during ship acceleration, deceleration and crash stop has been investigated. Results show that, during dynamic processes, the engine could be thermally overloaded even if the engine power trajectory is inside the static engine operating envelope. The paper contributes to finding proper indicators for thermal overloading of modern two-stroke marine diesel engines. It is demonstrated that when matching the engine with the propeller and designing the ship propulsion control system, not only the static engine operating envelope, but also the dynamic engine behaviour should be considered.

Ship designers hardly ever receive feedback from the actual operation of their designs apart from sea acceptance trials. Similarly, crews operating the vessels do not receive a clear picture of the energy performance and environmental footprint of different options. This paper proposes a methodology based on operational data from continuous monitoring, and applies it to an ocean patrol vessel of the Royal Netherlands Navy in order to identify the impact of diverse operational conditions on energy performance over the whole operating range, but also to examine the decision to equip the vessel with hybrid propulsion. Specifically, it introduces mean energy effectiveness indicator and mean total energy efficiency over discretised vessel speed, as the main tool in quantifying the energy gains and losses to assist in making better-advised design and operational decisions. Moreover, it demonstrates a dataset enrichment procedure, using manufacturers' information, in case not all needed sensors are available. Results suggest that electrical propulsion was 15–25% less efficient than the best mechanical propulsion mode, and on the overall energy performance of the vessel, increasing speed by 1 knot caused a 7% and 14% increase over the minimum (Formula presented.) /mile emissions between 8 and 14, and above 14 knots respectively.

As shipping is setting sail for a sustainable future, the application of fuel cells is increasingly regarded as a promising technology to reduce or fully eliminate emissions. Fuel cells convert the chemical energy in fuels directly into electricity, achieving high efficiencies while emitting no hazardous compounds and producing little noise and vibrations. This chapter provides an overview of different fuel cell systems and discusses the various fuel cell types, working principles and characteristics. Particular attention is given to the low and high temperature polymer electrolyte membrane fuel cell and solid oxide fuel cell, as these are often considered to hold most potential for application in ships. The application of fuel cells is not restricted to the use of pure hydrogen, thus an overview of relevant fuel processing and purification technologies is provided as well. Operational aspects including electrical efficiency, part load performance, load transients, system start-up, heat recovery and combined cycle operation are introduced and subsequently discussed in the context of maritime application. Aspects related to ship design and operation, emission regulation compliance, reliability, availability, maintenance, safety and economics are briefly considered. Finally, an overview of relevant maritime experience and a future outlook are provided.