• Energy Research

Recently, the marine industry has been under a paradigm shift toward adopting increased automation, and initiatives to enable the autonomous operations of ships are ongoing. In these cases, power plants require advanced monitoring techniques not only for the performance parameters but also to assess the health state of their critical components. In this respect, this study aims to develop a monitoring functionality for power plants that captures the performance metrics while considering the overall system and its components’ reliability. A hybrid power plant of a pilot boat is considered a case study. A rule-based energy management strategy is adopted, which makes the decisions on the power distribution to the investigated power plant components. Additionally, a dynamic Bayesian network is developed to capture the temporal behavior of the system’s/components’ reliability accounting for the power plant’s operating profile. Results demonstrate that the selected hybrid power plant monitoring capabilities are enhanced by providing the power plant performance along with the estimation of the system’s health state. Furthermore, these extended monitoring capabilities can provide the essential metrics to facilitate decision making, enabling the autonomous operation of the power plant.

In April 2018, the International Maritime Organisation adopted an ambitious plan to contribute to the global efforts to reduce the Greenhouse Gas emissions, as set by the Paris Agreement, by targeting a 50% reduction in shipping’s Green House Gas emissions by 2050, benchmarked to 2008 levels. To meet these challenging goals, the maritime industry must introduce environmentally friendly fuels with negligible, or low SOX, NOX and CO2 emissions. Ammonia use in maritime applications is considered promising, due to its high energy density, low flammability, easy storage and low production cost. Moreover, ammonia can be used as fuel in a variety of propulsors such as fuel cells and can be produced from renewable sources. As a result, ammonia can be used as a versatile marine fuel, exploiting the existing infrastructure, and having zero SOX and CO2 emissions. However, there are several challenges to overcome for ammonia to become a compelling fuel towards the decarbonisation of shipping. Such factors include the selection of the appropriate ammonia-fuelled power generator, the selection of the appropriate system safety assessment tool, and mitigating measures to address the hazards of ammonia. This paper discusses the state-of-the-art of ammonia fuelled fuel cells for marine applications and presents their potential, and challenges.

Dual fuel engines constitute a viable solution for enhancing the environmental sustainability of the shipping operations. Although these engines comply with the Tier III NOx emissions regulations when operating at the gas mode, additional measures are required to ensure such compliance at the diesel mode. Hence, this study aimed to optimise the settings of a marine four-stroke dual fuel (DF) engine equipped with exhaust gas recirculation (EGR) and air bypass (ABP) systems by employing simulation and optimisation techniques, so that the engine when operating at the diesel mode complies with the ‘Tier III’ requirements. A previous version of the engine thermodynamic model was extended to accommodate the EGR and ABP systems modelling. Subsequently, a combination of optimisation techniques including multiobjective genetic algorithms (MOGA) and design of experiments (DoE) parametric runs was employed to identify both the engine and the EGR/ABP systems settings with the objective to minimise the engine brake specific fuel consumption and reduce the NOx emissions below the Tier III limit. The derived simulation results were employed to analyse the EGR system involved interactions and their effects on the engine performance and emissions trade-offs. A sensitivity analysis was performed to reveal the interactions between considered engine settings and quantify their impact on the engine performance parameters. The derived results indicate that EGR rates up to 35% are required, so that the investigated engine with EGR and ABP systems, when operating at the diesel mode, achieves compliance with the ‘Tier III’ NOx emissions, whereas the associated engine brake specific fuel consumption penalty is up to 8.7%. This study demonstrates that the combination of EGR and ABP systems can constitute a functional solution for achieving compliance with the stringent regulatory requirements and provides a better understating of the underlined phenomena and interactions of the engine subsystems parameters variations for the investigated engine equipped with EGR and ABP systems.

The immense pressure to decarbonise the maritime industry has led to the Liquefied Natural Gas (LNG) uptake as a marine fuel and the LNG fuelled ships design. As LNG is stored in cryogenic conditions, the heat ingress from the ambient causes the boil-off gas (BOG) production, which, if not controlled, results in the tank overpressure with implications on the fuel storage system safe operation. This study aims at investigating an LNG storage tank behaviour for realistic operating conditions of an LNG fuelled ocean-going ship, targeting to identify the recommended control actions for avoiding tank overpressure. A dynamic model is developed by considering the mass and energy conservation in the liquid and vapour subsystems, the energy conservation in the tank walls, the vapour to liquid equilibrium (VLE), and real gas properties. Following the model validation for a holding test, simulation runs were performed for various operating conditions corresponding to typical long and short voyages of the investigated ship. The simulation results demonstrate that a boil-off gas (BOG) compressor capacity of 450 kg/h along with its on/off control setting the upper and lower limits of the tank absolute pressure at 5.5 and 4 bar leads to tank overpressure avoidance and the minimum number of BOG compressor activations.

Methanol use in marine engines is associated with challenges pertaining to misfiring and knocking. This study aims at parametrically optimising a marine dual-fuel four stroke engine considering variable compression ratio (VCR) settings and methanol direct injection with 90 % energy fraction. CFD models are developed and validated against experimental data. Parametric runs are employed in 20, 55 and 90 % load, with compression ratio ranging 11–19, to reveal the optimal CR values for each load considering the engine performance and emissions parameters along with constraints on combustion efficiency and stability. The sustainability index is employed to assess the environmental sustainability of the engine under optimal VCR settings compared to FCR. The results reveal that the engine thermal efficiency for CR 19, 16 and 12 at low, medium and high loads respectively increases by 7 %, 2 % at low and medium loads, whereas, decreases by 4 % at the high load. The engine with the proposed VCR settings achieves the compliance with the IMO Tier III limits and increases its sustainability index by 21 % compared to the fixed compression ratio. This study provides insights for the effective use of high methanol energy fractions in marine dual engines, thus contributing to the shipping sector sustainability.

In this article, the mapping of the performance and emission parameters of a merchant vessel propulsion system over the ship operating envelope was carried out by using a model capable of representing the ship propulsion system behaviour. The model was developed based on a modular approach and was implemented in the MATLAB/Simulink environment. The various parts of the propulsion engine as well as the shafting system, the propeller and ship hull were represented by separate submodels having the appropriate interface for exchanging the required variables to each other. The output of the model includes the performance and emission parameters of the engine as well as the operating parameters of the propeller and ship. Initially, the propulsion engine operation under steady-state conditions was simulated and the predicted engine performance parameters results were validated. Then, simulations of the ship propulsion system operating points at various resistance curves were performed. Based on the derived results, the mapping of the ship propulsion system performance and emission parameters was presented and their variation throughout the ship operating envelope was discussed. Finally, an example of using the derived results in order to minimise the fuel consumption and CO2 emissions for a typical ship route is presented and discussed.

The shipping sector has been under great pressure since the last decade to improve its environmental footprint, more so recently with the International Maritime Organisation target for a 50% reduction in greenhouse gas emissions by 2050, benchmarked to 2008 levels. These challenging goals have increased the interest towards alternative fuels and ship energy systems that can offer a more sustainable performance. The variety of potential technological solutions along with the multiple criteria employed to evaluate the ship energy systems with respect to sustainability considerations, renders the decision-making process for selecting ship energy systems challenging and highlights the need for dedicated decision support methods. This study presents a state-of-the-art review of the literature on decision support methods for enhancing the ship energy systems sustainability. The trends and gaps in the literature are identified, based on which, recommendations for future research are proposed. This study findings indicate that, among others, further research is needed to adapt more holistic approaches that include safety and reliability indicators as well as the social aspect of sustainability. This review can be beneficial for the maritime industry stakeholders, including policy makers, academics and ship owners/operators.