Various techniques are used to reduce harmful pollutants such as NO_X emissions from ships. Selective catalyst reduction (SCR) systems are the most effective technique used to reduce NO_X emissions. In this study, the effects of an SCR reactor on NO_X emissions and performance in high-pressure selective catalytic reduction (HP-SCR) systems were investigated numerically. In numerical studies, the effects of SCR system diameter, output form, catalyst activation energy, mixing zone length, and location were investigated as parametric, and the most suitable system geometry was determined. The effects of geometric parameters and catalyst type on emission and performance such as NO_X reduction, NH₃ slip, velocity, and pressure loss were investigated. It was determined that with increasing system diameter, whereas the NO_X reduction performance increased depending on exhaust velocity, the pressure drop decreased, and the most suitable system diameter was determined as 780 mm. Furthermore, the obtained results showed that the performance of NO_X reduction decreased after 2 × 10⁶ kJ/kmol activation energy, and the most suitable SCR output form was conical geometry. In terms of the environment, this study will contribute to achieving the UN Sustainable Development Goals such as climate action (SDG 13).

In the maritime sector, many improvements are performed on ship propulsion system. The hybrid propulsion system (HPS) is one of the innovations in the marine sector, considering International Maritime Organization (IMO) energy efficiency measures. The main objectives of the HPS are reduction in fuel consumption, maintenance costs, and minimization of the emissions of gases that harm the environment. The IMO International Convention for the Prevention of Pollution from Ships (MARPOL) Annex VI “Prevention of Air Pollution from Ships” determines nitrogen oxide, sulfur oxide, and particulate matter limits emitted from marine vessels. These limitations will be met with the HPS to be established on marine vessels. Batteries, an Energy Storage System (ESS), are used to drive electric motors, part of the HPS equipment. In this study, battery types are evaluated in terms of their chemical properties, capacities, volumes, weights, energies, specific energies, costs, and life cycle by TOPSIS method and the most suitable battery for the HPS is selected. According to the results, the highest rank (0.643127638) for the HPS is obtained from lithium iron phosphate (LFB) battery that has 200 Ah capacity, 30.55-liter volume, 27.7 kg weight, 92.42 Wh/kg energy density, 987 $/kWh cost, and 400~13,000 life cycle. This study will be a good source for researchers and maritime sector stakeholders, whose studies regard Energy Storage Systems, especially batteries on the HPS in marine vessels.

The harmful effects of gas emissions, resulting from the consumption of fossil fuels, on the environment continue to increase. In order to reduce these effects, new regulations are implemented in the field of maritime and it is getting harder to comply with these regulations. The fact that the technological developments in conventional propulsion systems come to a head and become insufficient especially when environmental factors are taken into consideration, has led researchers to work in the field of electrical propulsion systems. There are many studies examining the historical process and development of electrical propulsion systems. In this literature study, the history of the Diesel-Electric propulsion system, which has an important place in electrical propulsion systems, is explained and the change and development of this system, especially in the last 20 years, and its comparison with other electrical propulsion systems are discussed. It has been shown that Diesel-Electric propulsion system, which has succeeded to be an important propulsion system alternative for many ship types, can have different advantages with technological developments

The implementation of hybrid propulsion systems in vessels has gained prominence due to their significant advantages in energy efficiency and their reduction in harmful emissions, particularly during low engine load operations. This study evaluates hybrid propulsion system applications in two different tugboats, focusing on fuel consumption and engine load across eight distinct operational scenarios, including Istanbul Strait crossings and towing and pushing manoeuvres. The scenarios incorporate asynchronous electric motors with varying power ratings, lead-acid and lithium iron phosphate batteries with distinct storage capacities, and photovoltaic panels of different sizes. The highest fuel savings of 72.4% were recorded in the second scenario, which involved only towing and pushing operations using lithium iron phosphate batteries. In contrast, the lowest fuel savings of 5.2% were observed in the sixth scenario, focused on a strait crossing operation employing lead-acid batteries. Although integrating larger-scale batteries into hybrid propulsion systems is vital for extended ship operations, their adoption is often limited by space and weight constraints, particularly on tugboats. Nevertheless, ongoing advancements in hybrid system technologies are expected to enable the integration of larger, more efficient systems, thereby enhancing fuel-saving potential.

The study aims to investigate the effects of operational parameters such as nozzle opening pressure and fuel injection timing on exhaust emissions of a single cylinder diesel engine fuelled with distilled marine fuels. Tests were performed on a single cylinder, 13 kW, natural aspirated, direct injection and air cooled diesel engine at 1600 RPM constant engine speed. The tests were conducted for three different nozzle opening pressures (20, 22 and 24 MPa) and 3 different nozzle opening pressures (25° bTDC, 20° bTDC and 15° bTDC). The experiments were repeated at least three times to increase the reliability of the results. The results of the study show that increasing nozzle opening pressure increases the BTE and NOx emissions whereas decreases CO emissions, specific fuel consumption and exhaust gas temperature. Advancing fuel injection timing reduces the CO emissions but increases NOx emissions. The paper provides detailed test results, explanations and discussion.

1. Given that maritime transport accounts for the majority of global cargo movement, its substantial reliance on fossil fuels raises significant concerns regarding its contribution to global warmin...