As navies and maritime organisations transition towards low-emission propulsion systems, spark-ignited (SI) gas engines capable of operating on sustainable, low-reactivity fuels are gaining renewed interest. These engines, while offering potential for fossil-free operation, present significant challenges under transient conditions due to complex interactions between throttle control, fuel regulation, and combustion stability. Accurate dynamic modelling is critical to integrate these engines into resilient naval power systems and to support the development of advanced control strategies. This study evaluates several high-fidelity mean value first principle engine modelling (MVFPEM) approaches for simulating the dynamic gas path behaviour of a large, high-speed, SI marine engine under rapid load changes. Models with varying levels of complexity, including simplified and full turbocharger implementations and different gas path volume resolutions, were calibrated using a single measurement campaign and validated against measured transient data. Several methods for turbocharger performance mapping (Stapersma, Casey & Robinson, and Jensen) were evaluated for their applicability in predicting the engine behaviour in dynamic operating scenarios. The results highlight that models incorporating three control volumes and full turbocharger dynamics achieve the highest accuracy, particularly during rapid load increases and recovery phases. Simplified models fail to capture turbocharger inertia and pressure transients, limiting their applicability to investigate naval propulsion or electric power generation plant behaviour under transient load conditions. This work provides guidance on selecting and validating engine models for marine applications and reinforces the role of high-fidelity MVFPEMs in the design and simulation of future naval energy systems.

Methanol has emerged as a promising sustainable fuel for shipping, with the premixed dual-fuel (PRDF) strategy holding strong potential for deploying it in marine internal combustion engines. However, achieving high methanol energy fractions (MEFs) remains challenging due to combustion stability issues, which limit efficiency and operating robustness. Experimental insights into high-MEF operation are scarce, particularly for large-bore engines, leaving critical knowledge gaps in understanding combustion and performance characteristics of methanol PRDF engines. This study addresses these gaps through an experimental investigation on a marine-scale single-cylinder engine, operating with up to 93% MEF and high-load conditions. Two distinct MEF operational ranges were identified, with different mechanisms limiting each boundary. Poor combustion performance and elevated unburned hydrocarbon emissions emerged as the primary factors limiting high MEFs and were more sensitive to pilot ignition timing than to ignition energy. Although energy from premixed combustion Phase I decreased from 25% at 79% MEF to 6.2% at 93% MEF at maximum load, advancing ignition by a shortened ignition delay (from 9.2 °CA to 4.4 °CA) improved combustion efficiency (from 87.9% to 92.7%) and gross indicated thermal efficiency (from 43.4% to 45.3%). A novel framework was applied to analyze heat release profiles, combining qualitative assessment with a quantitative methodology based on two morphology metrics. This approach revealed three distinct combustion modes—characterized by m-, h-, and n-shaped profiles—unique to methanol PRDF operation, each linked to specific underlying mechanisms, and provides a systematic tool for combustion mode classification.

Hybrid propulsion is considered a reliable alternative to solely mechanical or electrical propulsion for enhanced ship energy performance. Nevertheless, an increased number of components and interconnections results in more complex ship design problems. The automotive and aviation industries already examine new designs on predefined driving and flying cycles. However, new ships are still assessed on one design point with the regulated Energy Efficiency Design Index (EEDI). Its limited consideration of calm water conditions and installed rated power is characterised as insufficient, if not dangerous. A design methodology that accounts for operational and environmental uncertainty is lacking. This paper proposes a design optimisation framework for the topology selection and sizing of hybrid propulsion systems integrating probability distributions of actual sailing profiles from continuous monitoring. The methodology is demonstrated on the ‘Holland’ class ocean patrol vessels of the Royal Netherlands Navy. Its multi-objective consideration examines a wide design space from an environmental, financial, and technical perspective, solving the mixed-integer nonlinear programming (MINLP) problem with a multi-starting scheme that combines a genetic algorithm and interior point method. The low computational cost is achieved by integrating a state-of-the-art digital twin approach leveraging data-driven and first-principle modelling. The results demonstrate feasible improvements of approximately 4 % for carbon intensity and 11 % for operational expenditure by increasing the size of the electrical motors. The exact configuration and percentage improvement are sensitive to actual operational and environmental conditions, while calm water conditions tend to overestimate savings. Consequently, the use of actual sailing profiles is recommended for more accurate life-cycle predictions.

The maritime sector aims to achieve short and medium-term sustainability targets through the conversion of Internal Combustion Engines to methanol operation. For small to medium sized engines, Port Fuel Injection (PFI) is the most viable injection method to achieve this conversion. However, the knowledge of the behaviour of methanol in combustion engines, particularly its spray characteristics under PFI conditions, is limited. To better understand liquid methanol sprays, this paper studies the injection of methanol in marine PFI conditions through Computational Fluid Dynamics (CFD) modelling. The CFD models use the Lagrangian-Eulerian (LE) coupling method within the Reynolds Averaged Navier Stokes (RANS) turbulence framework. Numerical results were validated using dedicated methanol experiments from the literature for both high and low injection pressures. Subsequently, this predictive CFD framework was used in a number of different injection pressures with scaled injection quantities that represent marine applications. Moreover, we demonstrated that high injection pressure improves atomisation and, thus, evaporation prior to wall impingement. This work strongly contributes to our understanding of marine PFI methanol engines by modelling fuel quantities relevant for ship applications. Our approach can be implemented in full engine simulations to solve evaporation challenges often found in small-bore methanol marine engines.

Marine natural gas SI engines are a potential solution for mitigating GHG impacts of the maritime sector.
However, SI engines encounter challenges related to combustion stability, including knocking and partial burning. Employing fast thermodynamic simulation models can aid in understanding the combustion characteristics of these engines and identifying optimization routes. Previous studies have shown that these converted engines exhibit three distinct combustion stages due to the different transport and chemical phenomena occurring when cylinder geometry remains unchanged.
This study aims to utilize this approach to characterize the combustion of a converted marine NG-fueled SI engine using a multi-Wiebe modeling approach. In this paper, we developed a closed in-cylinder thermodynamic model based on measurements from a 500 kW marine NG-SI engine and validated it through additional measurement points. Furthermore, we analyzed the impact of operating parameters such as spark timing (ST) and air excess ratio (λ) on the Wiebe parameters and their corresponding combustion stages.
Our findings indicate that the triple-Wiebe modeling approach effectively simulates the combustion processes in this type of NG-SI marine engine. Additionally, diluting the mixture increased the shape factor of all three Wiebe functions. The first combustion stage was found to be the most sensitive to both dilution and delayed ST effects, as reflected by the Wiebe parameters. This sensitivity may explain the observed deterioration in combustion and emission performance, as more fuel combusts in the later combustion stage. In our efforts to accelerate the defossilization of the shipping industry, this study highlights the importance of various combustion modeling approaches in understanding and optimizing the performance of marine SI engines.

Emerging clean fuels with high octane rating make spark ignition (SI) technology a promising candidate for heavy-duty applications. The conversion of existing diesel engines to SI operation can accelerate the adoption of these fuels. This study investigates the combustion characteristics of a 500 kWe marine lean-burn (LB) homogeneous charge SI engine with a flat cylinder head and a hemispherical bowl-in piston. It focuses on the relationship between fuel distribution and phasing across the distinct bowl-in and squish combustion phases and their impact on efficiency and emissions in multicylinder engines. The effects of air excess ratio, spark timing, and intake air temperature are systematically assessed. Dedicated measurements of methane and total unburned hydrocarbon emissions enable a comprehensive evaluation of combustion performance and emissions. Results confirm the presence of a slower squish phase, differing from conventional SI engines, and highlight the influence of the squish region's surface-to-volume ratio on flame propagation. The sensitivity of combustion behavior to control parameters such as air excess ratio and ignition timing is demonstrated, with notable differences: while richer mixtures advance bowl-in and squish phases, earlier ignition timing delays the squish phase. Despite this, both mixture enrichment and ignition timing advancement improved performance, increasing brake thermal efficiency by 25% and 10%, respectively. Methane emissions remained within typical ranges for marine SI engines and NO_x emissions met Tier III limits at nominal conditions; yet the persistent challenge of methane slip underscores the need for more comprehensive regulatory standards addressing both CH₄ and NO_x emissions.

Renewably produced methanol is a promising fuel for internal combustion engines in long-range transportation thanks to its scalability, liquid storage, and favorable combustion properties. However, the distinction between different injection and ignition strategies for methanol engines and the resulting combustion mechanisms has not been consistently defined. Moreover, diffusion combustion strategies are favored over premixed strategies in large engines because of higher methanol energy fractions, disregarding the advantages of premixed approaches, such as reduced nitrogen oxide emissions and retrofitting opportunities. To address ambiguity in terminology, this paper proposes a classification framework for injection and ignition strategies and applies it to methanol-fueled internal combustion engines. Subsequently, this review focuses on experimental studies of methanol-fueled heavy-duty engines, which are crucial for transitioning to renewable and sustainable energy in long-range transportation. This research summarizes the impact of the reviewed injection and ignition strategies on combustion characteristics, engine performance and emissions to identify key trends. Furthermore, this review highlights how specific design and operating parameters influence premixed dual-fuel combustion, offering insights into optimizing performance and emissions. While mono-fuel and premixed dual-fuel strategies with methanol can significantly promote methanol use in heavy-duty engines and reduce harmful emissions like nitrogen oxides, a rise in unburned hydrocarbon emissions may also be expected, necessitating further research in this area. Additionally, methanol injection location in premixed dual-fuel schemes affects its cooling effect, influencing volumetric and thermal efficiency. Overall, this study deepens our understanding of methanol's impact on heavy-duty engine performance, highlighting critical challenges to be addressed for advancing sustainable transportation.

Waterborne transportation has long been the backbone of global trade, with the reciprocating internal combustion engine (ICE) as the dominant power source. In the efforts to decarbonize shipping, methanol has emerged as a promising alternative fuel due to its easy storability and favorable combustion characteristics compared to non-carbon fuels such as hydrogen and ammonia. In the MENENS project, one of the research objectives is to better understand, further develop, and demonstrate different engine technologies that can employ methanol fuel in marine-sized engines. This study reviews maritime stakeholder research on methanol fuel for marine ICEs, emphasizing the chosen injection and ignition strategies across different engine technologies. In this paper, we aim to identify research gaps concerning methanol as a marine engine fuel, and provide insight into the initiatives and proposed research direction within MENENS.

A key factor towards zero-emission shipping is the adoption of electric propulsion with hybrid power sources. The heterogeneous power sources of modern electric vessels require optimal energy management systems, as conventional rule-based control in hybrid energy systems may result in suboptimal solutions with limited flexibility. Advanced optimal control strategies offer a promising avenue to address this issue. This paper presents a novel control strategy based on the Equivalent Consumption Minimization Strategy for a dual-fuel full-electric vessel operating with diesel engines and hydrogen fuel cells taking into account both fuel cost and NOx emissions. The effectiveness of the developed controllers is evaluated against a benchmark derived from state-of-the-art strategies in a simulation study using real-world data. The results highlight the controller's performance, as well as the operator's choice by selection of weights for the objectives. The proposed control strategy achieves nearly 2 % fuel savings compared to a single-objective rule-based controller. It also exploits the potential for up to 45 % reductions in NOx emissions. When both objectives are combined, the controller still delivers over 0.5 % fuel savings while reducing NOx emissions by nearly 15 %. If a financial cost is assigned to emissions, the total operational cost savings increase to more than 4 %.

The development of DC protection systems is an enabler of widespread adoption of DC microgrids. This paper introduces a three-level gate driver that provides the latching current limiter functionality in a solid-state circuit breaker with unidirectional protection. The proposed gate driver combines the output port description of a well-known, enabled gate driver with a soft turn-off network. The corresponding circuit can be adapted to well-established SSCBs, requiring few modifications which could allow for quick development. The concept, simulation, implementation and experimental validation of the gate driver are in the scope of the paper. The gate driver is implemented and tested in a solid-state circuit breaker prototype, showing the potential to develop further DC protection devices.

To reduce emissions, methanol is a favorable carbon-neutrally-producible alternative fuel, which can substitute gasoline in direct-injection spark-ignition (DISI) engines. Robust DISI engine operation relies on a consistent air-fuel mixture. To understand the physical processes that characterize the mixture formation, predictive computational fluid dynamics (CFD) simulations are used to improve the understanding, operation, and emissions of these engines. However, using an alternative fuel such as methanol often poses challenges to the CFD simulations’ validity due to the alteration of the fuel properties. This study presents the validation of a CFD modeling approach that can be applied to the predictive modeling of DISI methanol engines. Our methodology uses Lagrangian-Eulerian methods to model the methanol eight-hole counter-bore style Spray M injector from the Engine Combustion Network (ECN). We used the Spray M1 condition, which represents a late-injection spray under a high ambient pressure and temperature environment. For the present study, we employed both a Reynolds Averaged Navier Stokes (RANS) and a Large Eddy Simulation (LES) turbulence approach in CONVERGE-CFD. To validate our models, we used the projected liquid volume (PLV) maps generated by the tomographic liquid volume fraction (LVF) based on methanol. Subsequently, we tuned our models based on the corresponding numerical predictions of the liquid penetration and LVF distributions. The results demonstrated that both the RANS and LES models could replicate the spray morphology and liquid length. While the RANS model was unable to fully capture the complex phenomena of spray collapse and sweeping in the methanol multi-hole spray, the LES model effectively reproduced these behaviors without excessive tuning effort.

Spark-ignition (SI) engines emerge as a viable solution for specific marine applications, offering low-noise operation and emissions mitigation, as well as great potential to utilize high-octane number alternative fuels, such as methanol, ammonia, and hydrogen. However, heavy-duty (HD) SI engines still face challenges such as knocking and combustion instability. Particularly for lean combustion conditions, these engines exhibit the most pronounced cyclic combustion variations. This paper investigates the combustion stability of a 500 kW marine lean-burn natural-gas (NG) engine, a promising candidate for reducing emissions in marine applications. We focus on analyzing in-cylinder pressure measurements to quantify combustion characteristics, emphasizing cycle-to-cycle combustion variation, and exploring the influence of operating parameters like spark timing (ST) and air excess ratio (λ). Our findings demonstrate a clear trade-off between NO_x and COV_IMEP emissions through variations in the λ and ST. We identified a transition zone characterized by an increasing number of late-burning cycles at higher λ, before partial burning cycles began at further dilution. Following this, we established a new threshold of 6% for COV_IMEP to determine unstable combustion. Notably, increasing dilution from a λ of 1.12 to 1.61 decreased NO_x emissions from 17.83 g/kWh to 0.16 g/kWh, well below IMO Tier III standards, while COV_IMEP increased from 1.72% to 13.42%. These insights highlight the potential for advancing SI technology for marine applications and the need for further research to optimize both combustion and emissions in such engines.

The third Naval Engineering and Ship Control special edition of the Journal of Marine Engineering and Technology aims to present cutting-edge research on naval engineering and ship control, as was presented during the International Naval Engineering Conference and Exhibition (INEC) and the International Ship Control Systems Symposium (iSCSS), held together in Delft in 2022.

The global shipping industry is at a crucial juncture, facing an urgent need to reduce greenhouse gas emissions in the short to medium term to mitigate climate change. A shift towards alternative fuels is imminent, necessitated by the limitations in current fuel cell and battery technology in terms of power density. Addressing this, navies worldwide are not only exploring the use of alternative fuels to diminish environmental impact but also seeking solutions to reduce emissions signatures and decrease reliance on fossil fuels. In this paper, we investigate the use of hybrid turbocharging to improve the dynamic performance of alternatively fueled combustion engines. We extended an existing and validated Mean Value First Principle (MVFP) engine model of a spark-ignited (SI) throttle-controlled Caterpillar 3508A gas engine with a hybrid turbocharger. The study investigates the impact of electrical power Power-Take-In/Off from the turbocharger shaft on the engine’s air path dynamics for different use cases, considering transient and steady state phases. We demonstrate that a generator set can benefit from hybrid turbocharger by significantly reducing the engine speed drop and settling time after a load step. While accelerating from 0 to cruise speed, propulsion engines benefit less from hybrid turbocharger, due to risk of compressor surge during low engine speeds. The overall results show that simply adding electric power to the turbocharger shaft during transient phases does not unlock the full potential of hybrid turbocharging for alternatively fueled combustion engines. The implementation of hybrid turbocharging requires careful integration, reconsideration of sizing and matching of turbine and compressor, and the combination with blow-off, blow-by, and waste gate valves to prevent compressor surge. However, the capability for electrical power take-off/in within a larger propulsion and electrical power generation plant context suggests a reduction in spinning reserves and an increase in overall system efficiency during steady state. Thus, implementing hybrid turbocharging can play an important role in the transition to alternative fuels and the reduction of greenhouse gas emissions.

The path to zero-emission shipping is deeply connected to full-electric vessels. One major challenge to enable this technology for broader application is the design of optimal energy management (EM). The flexibility of operating load sharing in hybrid energy systems could lead to suboptimal solutions using rule-based control. Advanced control strategies can be used to find optimal solutions for the EM problem. In addition, the use of advanced control allows for the incorporation of multiple objectives. An important compromise is the decision between minimizing cost and emissions. A promising approach for EM is the Equivalent Consumption Minimization Strategy (ECMS), which allows for instantaneous optimization of the problem and is suitable for dealing with fast system dynamics. The strategy assigns equivalent factors in the objective function, leading to an easily expandable multi-objective control approach.This paper presents a novel ECMS-based control strategy for health-aware EM of a full-electric vessel, incorporating diesel internal combustion engines, fuel cells, and batteries with flexible changing operation conditions. To this aim, firstly, we introduce our innovative formulation of the multi-objective problem, considering fuel and electricity expenditures and CO₂ and NO_x emissions, alongside the degradation of batteries and fuel cells. Subsequently, we determine the equivalent factors by employing a Pareto Front approach. Lastly, our developed controllers are assessed against a benchmark derived from state-of-the-art strategies. A case study of a full-electric vessel showcase the potential of our proposed solution. The results demonstrate the control's effectiveness in optimizing the operation considering a variety of objectives, such as fuel consumption or emission production, under variable operational conditions.

This paper proposes an integrated gate driver featuring soft turn-off and current limiting for a solid-state circuit breaker in primary shipboard DC systems. The added functionalities allow solid-state circuit breakers to mitigate part of the voltage resonances caused by a hard turn-off, and to reduce unnecessary tripping during overloading events. The proposed design is based on well-known DC protection strategies, which are enhanced by the custom gate driver, simulated in SPICE software. The paper shows that the proposed strategy effectively attenuates the adverse effects of the hard turn-off present in popular off-the-shelf devices, while effectively breaking the fault current. The low propagation delay of the selected components facilitates the rapid break of the current, reaching approximately 69A peak. In addition, the latch current limiter prevents the feeder from overloading, creating a voltage drop of 51% for tens of nanoseconds. The results are promising in motivating future prototyping of the design in an attempt to accelerate the acceptance of shipboard DC systems.

The protection of DC systems in mobility applications, such as land transport, aircraft, and shipping, presents significant challenges due to the need for high power density equipment in confined spaces. This paper focuses on DC systems on board ships, for which diverse applications require different power levels, architectures, and protection strategies. Existing protection frameworks and regulations are often inadequate or outdated for the field, leading to certification issues and insufficient fault analysis. This research proposes a use case-based categorization of short circuit currents for primary systems. A reference scenario is created using a simulation model of a 5 MW system in a superyacht to provide a short circuit inventory. The study proposes three contributions. A comprehensive fault inventory, a qualitative categorization, and relevant recommendations for power converter design. The research highlights the importance of fault categorization in understanding the impact of various short circuits on shipboard DC systems. The study emphasizes the importance of the evolution of materials and power converters in developing efficient protection technologies for ships. This work addresses some fundamental gaps in shipboard DC systems, providing a foundation for improved protection strategies and regulations, ultimately contributing to the advancement of protection of shipboard DC systems.

The sustainability policy requires the Netherlands Ministry of Defense (MoD) to become largely independent of fossil fuels in the coming decades, while at the same time the geopolitical situation requires the Armed Forces to operate globally. Therefore, the Royal Netherlands Navy needs to reconsider its fuel strategy, to gradually change to energy carriers from renewable sources, and to redesign its power and propulsion system, both to improve efficiency and to reduce its emissions and signatures. The aim of this chapter is to provide a critical review of the challenges and opportunities of the transition to alternative energy carriers and energy systems and to provide a direction for the required research and development towards the future Navy fleet that can operate independently of fossil fuels and with minimal signature. First, the chapter reviews production, expected availability and projected development of cost of the various alternative fuels, with a specific focus on hydrogen, methanol, and renewable drop-in alternatives for naval distillate fuels, according to NATO F-76 spec- ifications. Subsequently, the chapter will discuss the impact of these three fuels on three differently sized navy vessels, that are currently considered for replacement: diving vessels, seagoing support vessels, and future surface combatants. For these three use cases, the chapter also discusses the potential power and propulsion system configurations and the opportunities to reduce signatures by alternative power supplies, such as fuel cells and batteries. Based on this analysis, the chapter will propose a fuel selection strategy for future navy vessels and will discuss the required research and development that is required to achieve the identified opportunities. The chapter closes with conclusions and recommendations on the route towards a future fleet that can operate globally independent of fossil fuels.

Methanol has emerged as a cost-effective and scalable alternative fuel for the maritime sector. However, the use of methanol in marine engines is limited by the unknown characteristics of methanol sprays when introduced through retrofitted port fuel injection (PFI) systems. The present study investigates the characteristics of methanol sprays under relevant conditions for marine engines, such as low injection pressure PFI. The primary objective of this research is to advance knowledge into key spray characteristics, including spray penetration, droplet size, atomization quality, and evaporation. The proposed methodology evaluates the efficacy of state-of-the-art computational fluid dynamics (CFD) models in simulating PFI marine engine spray conditions. Moreover, the study compares the performance of the Kelvin-Helmholtz (KH-RT) and Taylor Analogy Breakup (TAB) droplet breakup models under low injection pressure conditions. The results demonstrated that the KH-RT model does not predict any droplet breakup occurrence suggesting that the TAB model is more suitable for the given conditions. Furthermore, the liquid penetration of the spray was observed to align with the outcomes reported in previous experimental literature on methanol sprays. Nevertheless, the droplet sizes for low pressure injectors appear relatively large, indicating poor spray atomization, which impedes rapid evaporation and increases the risk of wall wetting in the inlet manifold and combustion chamber.

Optimal energy management is still a challenge in full-electric vessels. New degrees of flexibility in the energy management resulting from the load sharing between multiple, heterogenous power sources lead to a suboptimal solution using rule-based control. Therefore, advanced control strategies present a solution to the challenge of finding the optimal control input for a nonlinear multi-objective power and energy problem in sufficient time. As additional benefit, advanced control allows to incorporate multiple objectives in the optimization such as minimization of several emissions, operational costs, and component degradation. Equivalent Consumption Minimization Strategy (ECMS) is a strategy for instantaneous optimization, which is promising for applications in vessels with a high degree of uncertainty in the load profile. It incorporates multiple objectives by assigning equivalent cost factors in the cost function, allowing a flexible expansion of the control problem. In this paper, we present a novel ECMS-based control strategy for a full-electric vessel with the ability to react flexibly to changing mission conditions. First, we define the objectives for the control problem, in this study \ce{CO2} production, hazardous emission production, fuel consumption, energy cost, and the degradation of the battery.
Second, we develop a pareto-front approach for a-posteriori definition of the equivalent cost factors. To showcase energy consumption reduction, we use a benchmark control based on state-of-the-art control strategies. A full-electric case study vessel with high uncertainty in the load profile is chosen to evaluate the proposed controller. Several different load profiles are generated and tested to evaluate the performance of the ECMS controller in dealing with different types of loads. The results will demonstrate the effectiveness of the proposed novel control strategy in reducing energy consumption while minimizing other hazardous emission outputs and preserving the health of the battery.