Modern marine propulsion systems must be reliable, energy efficient, environmentally friendly, and economical. Efforts to reduce fuel costs and carbon dioxide (CO₂) emissions per nautical mile have a significant impact on the choice of propulsion system. Considering that there is no alternative for maritime transport, various technical and technological solutions are being considered that aim to improve efficiency and reduce the negative impact on the environment. One of the ways to achieve this goal is slow steaming, which reduces fuel consumption and CO₂ emissions. The designed speed of the vessel has a significant impact on the efficiency of slow steaming. Slow steaming is particularly suitable for large container ships with a design speed of more than 20 knots. In this paper, the effects of slow steaming are analyzed using the example of a container ship with diesel-engine propulsion. Propulsion systems with low-speed and medium-speed marine diesel engines with mechanical power transmission are investigated. Data on the required engine power and propeller speed were used for the study, obtained from calculations during testing of the ship’s hull model. The effects of speed reduction on specific fuel consumption and emission reduction were analyzed using numerical models of two-stroke and four-stroke diesel engines. The models were calibrated and validated using data provided by the engine manufacturers. The paper analyses four different cases where one or two low-speed diesel engines, or three or four medium-speed diesel engines, are used for propulsion. The analysis concludes that slow steaming can effectively reduce fuel consumption and CO₂ emissions, but the choice of the optimal propulsion system is highly dependent on maritime market conditions in maritime transportation. The choice of propulsion system affects the potential of slow steaming.

The energy efficiency and environmental friendliness of medium-speed marine diesel engines are to be improved through the application of various measures and technologies. Special attention will be paid to the reduction in NO_x in order to comply with the conditions of the MARPOL Convention, Annex VI. The reduction in NO_x emissions will be achieved by the application of primary and secondary measures. The primary measures relate to the process in the engine, while the secondary measures are based on the reduction in NO_x emissions through the after-treatment of exhaust gases. Some primary measures such as exhaust gas recirculation, adding water to the fuel or injecting water into the cylinder give good results in reducing NO_x emissions, but generally lead to an increase in fuel consumption. In contrast to the aforementioned methods, the use of an earlier inlet valve closure, referred to in the literature as the Miller process, not only reduces NO_x emissions, but also increases the efficiency of the engine in conjunction with appropriate turbochargers. A previously developed numerical model to simulate diesel engine operation is used to analyse the effects of the Miller process on engine performance. Although the numerical model cannot completely replace experimental research, it is an effective tool for verifying the influence of various input parameters on engine performance. In this paper, the effect of an earlier closing of the intake valve and an increase in inlet manifold pressure on fuel consumption, pressure and temperature in the engine cylinder under steady-state conditions is analysed. The results obtained with the numerical model show the justification for using the Miller processes to reduce NO_x emissions and fuel consumption.

The medium-speed diesel engine in diesel-electric propulsion systems is increasingly used as the propulsion engine for liquefied natural gas (LNG) ships and passenger ships. The main advantage of such systems is high reliability, better maneuverability, greater ability to optimize and significant decreasing of the engine room volume. Marine propulsion systems are required to be as energy efficient as possible and to meet environmental protection standards. This paper analyzes the impact of split injection on fuel consumption and NO_x emissions of marine medium-speed diesel engines. For the needs of the research, a zero-dimensional, two-zone numerical model of a diesel engine was developed. Model based on the extended Zeldovich mechanism was applied to predict NO_x emissions. The validation of the numerical model was performed by comparing operating parameters of the basic engine with data from engine manufacturers and data from sea trials of a ship with diesel-electric propulsion. The applicability of the numerical model was confirmed by comparing the obtained values for pressure, temperature and fuel consumption. The operation of the engine that drives synchronous generator was simulated under stationary conditions for three operating points and nine injection schemes. The values obtained for fuel consumption and NO_x emissions for different fuel injection schemes indicate the possibility of a significant reduction in NO_x emissions but with a reduction in efficiency. The results showed that split injection with a smaller amount of pilot fuel injected and a smaller angle between the two injection allow a moderate reduction in NO_x emissions without a significant reduction in efficiency. The application of split injection schemes that allow significant reductions in NO_x emissions lead to a reduction in engine efficiency.

The paper estimates the exhaust emissions of marine traffic in the port of Šibenik. The results of the analysis were obtained by including the following gaseous pollutants: nitrogen oxide (NOX), sulphur oxide (SOX), particulate matter (PM), volatile organic compounds (VOCs) and carbon dioxide (CO2) as greenhouse gas. In order to gain results and estimate the emission of harmful gases in the port of Šibenik, the passenger and the cargo throughput were taken into account. The activities of the ship during which the exhaust gases are emitted into the atmosphere are slow cruising in the reduced speed zone, manoeuvring and hotelling. The “bottom-up” method used in the emission estimation takes into account the ship’s engine power, engine load factor, fuel type, the emission factor, time of cruising and time hotelling in the port of Šibenik. The results of the analysis have shown that approximately 70 % of total emissions come from passenger ships (cruise ships) and 30 % from cargo ships.

The implementation of a system for the acquisition, transferring and processing of data essential for marine engine diagnostics is the basis of condition maintenance. Determining the most influential operating parameters, and conducting monitoring, analysis and taking action based on expert knowledge prevents downtime due to possible malfunctions. Timely corrections and replacements of worn parts based on condition diagnostics enable maintenance planning, which reduces the frequency of maintenance and the accumulation of unnecessary spare parts in warehouses. For research purposes, a system for remote data collection from electronically controlled marine engines was developed and applied. The system was installed on a four-stroke high-speed propulsion engine from a ferry, and the operating parameters of the engine were monitored during regular sailing in order to detect irregularities and possible failures at an early stage. The measurement system monitored the parameters obtained through the electronic engine control module via the J1939 protocol, and in this paper, the following relevant engine parameters were analyzed: engine speed, boost pressure, fuel consumption and engine load at the current speed. The analysis included the creation of trend diagrams to present the distribution of the minimum, median and maximum values of each parameter of all the measurements performed. This study also examined the simulation of the faults of the high-speed four-stroke marine engine model. By utilizing sensor data from critical system components, this research investigated different scenarios. The analysis aimed to elucidate the impact of these faults on engine performance. Based on the analyses of the relevant operating parameters of the engine, diagnostics were carried out.

Maintenance intervals and approaches for marine equipment have been the subject of numerous studies, focusing on previous failure patterns and associated risks. However, in vessels like drillships, operating under high reliability requirements and possessing significant redundancy, maintenance strategies have a critical impact on overall performance. This study investigates the influence of operational configurations on maintenance intervals and approaches for generator engine subcomponents onboard a drillship. Using data on injector failures onboard drillships, we employ the maintenance concept adjustment and design (MA-CAD) method to analyse and determine maintenance intervals across various operational configurations. Initially, we analyse the failure pattern of fuel injectors and propose a reduction in maintenance intervals through Weibull probability distribution fitting. Additionally, a risk analysis is conducted to assess the impact of operational configurations on risk indices related to fuel injector reliability and safety consequences. Our findings reveal that different operational configurations of the power generation plant can lead to changes in risk indices, shifting injector reliability status from unacceptable to undesirable limits. Consequently, maintenance intervals need to be adjusted as well to ensure optimal performance and safety. Furthermore, considering various engine subcomponents and their reliability under different operational configurations suggests the need for tailored maintenance approaches. This research provides insights into optimising maintenance strategies for drillship, ensuring reliability and safety across diverse operational scenarios.