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.

The current literature on solid oxide fuel cell and internal combustion engine (SOFC-ICE) integration is focused on the application of advanced combustion technologies operating as bottoming cycles to generate a small load share. This integration approach can pose challenges for ships such as restricted dynamic capabilities and large space and weight requirements. Furthermore, the potential of SOFC-ICE integration for marine power generation has not been explored. Consequently, the current work proposes a novel approach of SOFC-ICE integration for maritime applications, which allows for high-efficiency power generation while the SOFC anode-off gas (AOG) is blended with natural gas (NG) and combusted in a marine spark-ignited (SI) engine for combined power generation. The objective of this paper is to investigate the potential of the proposed SOFC-ICE integration approach with respect to system efficiency, emissions, load sharing, space and weight considerations and load response. In this work, a verified zero-dimensional (0-D) SOFC model, engine experiments and a validated AOG-NG mean value engine model is used. The study found that the SOFC-ICE integration, with a 67–33 power split at 750 kWe power output, yielded the highest efficiency improvement of 8.3% over a conventional marine natural gas engine. Simulation results showed that promising improvements in efficiency of 5.2%, UHC and NOx reductions of about 30% and CO₂ reductions of about 12% can be achieved from a 33–67 SOFC-ICE power split with comparatively much smaller increments in size and weight of 1.7 times. Furthermore, the study concluded that in the proposed SOFC-ICE system for maritime applications, a power split that favours the ICE would significantly improve the dynamic capabilities of the combined system and that the possible sudden and large load changes can be met by the ICE.

The shipping industry is facing increasing demands to reduce its environmental footprints. This has resulted in adoption of new and more environmental friendly power sources and fuels for on-board power generation. One of these novel power sources is the Solid Oxide Fuel Cell (SOFC) which has a great potential to act as a power source, thanks to its high efficiency and capability to handle a wide variety of fuel types. However, SOFCs suffer from low transient capabilities and therefore have never been considered to be used as the main power source for maritime applications. In this paper, novel component sizing, energy and power management approaches are proposed to enable the use of SOFCs as the main on-board power source for the first time in the literature and integrate them into the liquefied natural gas fueled Power and Propulsion System (PPS) of vessels. The proposed component sizing approach determines the power ratings of the on-board sources (SOFC, gas engine and battery) considering size and weight limits, while the energy and power management approaches guarantee an optimal power split between different power sources and PPS stability while looking after battery aging. The results indicate that the combined proposed optimization-based approaches can yield up to 53% CO₂ reduction and 21% higher fuel utilization efficiency compared to conventional diesel-electric vessels.

With increasingly stringent emission regulations, marine natural gas engines need to improve their performance. Various proven advantages of hydrogen-natural gas (H-NG) blends make them a promising enhanced fuel solution. Although modelling of H-NG combustion has been investigated before, mostly using CFD models, the literature on the modelling capabilities of Seiliger-based and Wiebe-based zero-dimensional (0-D) models is limited for H-NG combustion. Especially for the application of marine lean-burn spark-ignited (SI) engines. Therefore, the aim of this paper is to compare the capabilities of Seiliger-based and double Wiebe function-based 0-D models to capture H-NG combustion in a marine SI engine for different H-NG fuel blends, engine leaning (lean-burn operation) and engine loads. In this work, measurements on a turbocharged, SI marine natural gas engine were used to develop a heat release rate model, which was subsequently used as a basis for the Seiliger and double Wiebe function-based H-NG combustion characterization models. Results from the two combustion modelling approaches were compared for different H-NG fuel blends, engine leaning (lean-burn operation) and engine loads. The modelling results were also compared against engine measurements for different experimental conditions. This paper shows that the Seiliger modelling approach can be used to define different physical phenomenon in H-NG combustion, while accurately capturing the effects of hydrogen addition and engine leaning on the H-NG combustion process at varying engine loads. This research also found that the variations in late burn phase present in lean-burn NG and H-NG combustion can be captured using the double-Wiebe modelling approach, however, clear trends of the Wiebe combustion parameters for varying fuel blends and engine loads could not be identified to accurately capture the H-NG combustion process. Furthermore, Wiebe-based modelling approach produced larger errors in the estimations of work output and combustion heat for all test conditions.

Underwater exhaust systems are employed on board ships to allow zero direct emissions to the atmosphere with the possibility of drag reduction via exhaust gas lubrication. However, underwater expulsion of exhaust gases imparts high and dynamic back pressure, which can fluctuate in amplitude and time period as a ship operates in varying sea-states depending on its geographical location and weather conditions. Therefore, this research aims to experimentally investigate the performance of a marine diesel engine against varying amplitudes and time periods of dynamic back pressure at different sea-states due to underwater exhaust systems. In this study, a turbocharged, marine diesel engine was tested at different loads along the propeller curve against dynamic back pressure waves produced by controlling an electronic butterfly valve placed in the exhaust line after the turbine outlet. Engine performance was investigated against single and multiple back pressure waves of varying amplitudes and wave periods based on real sea-state conditions and wave data. We found that the adverse effects of dynamic back pressure on engine performance were less severe than those found against static back pressure. Governor control and turbocharger dynamics play an important role in keeping the fuel penalty and thermal loading low against dynamic back pressure. Therefore, a marine engine may be able to handle much higher levels of dynamic back pressures when operating with underwater exhaust systems in higher sea-states.

After-treatment technologies are adopted in automobiles and ships to meet strict emission regulations, which increase exhaust back pressure. Furthermore, underwater exhaust systems are employed on board ships to save space, and reduce noise and pollution on working decks. However, water at exhaust outlet creates a flow resistance for the exhaust gases, which adds to the back pressure. High back pressure reduces the operating limits of an engine, increases fuel consumption, and can lead to exhaust smoke. While the effects of back pressure were recognized earlier, there is a lack of experimentally validated research on the performance limits of a turbocharged, marine diesel engine against high back pressure for the entire operating window. The focus of this research is to provide a comprehensive understanding of back pressure effects on marine diesel engine performance, and to identify limits of acceptable back pressure along with methods to tackle high back pressure. In this work, a pulse turbocharged, medium speed, diesel engine was tested at different loads and engine speeds; against different values of static back pressure. Additionally, mean value model simulations could be validated and were used to compare the performance of a pulse and constant pressure turbocharged engine against high back pressures of 1 meter water-column (mWC), and for two different values of valve overlap. Using the validated simulation model, the conceptual basis for the engine smoke limit as well as for thermal overloading is investigated. A methodology applying the conceptual basis to define boundaries of acceptable back pressures has been presented in this paper. A combination of pulse turbocharger systems and small valve overlap showed to significantly improve back pressure handling capabilities of engines.