Marine Diesel Research Articles

Hydrogen Fuel Cell as an Electric Generator: A Case Study for a General Cargo Ship

In this study, real voyage data and ship specifications of a general cargo ship are employed, and it is assumed that diesel generators are replaced with hydrogen proton exchange membrane fuel cells. The effect of the replacement on CO2, NOX, SOX, and PM emissions and the CII value is calculated. Emission calculations show that there is a significant reduction in emissions when hydrogen fuel cells are used instead of diesel generators on the case ship. By using hydrogen fuel cells, there is a 37.4% reduction in CO2 emissions, 32.5% in NOX emissions, 37.3% in SOX emissions, and 37.4% in PM emissions. If hydrogen fuel cells are not used instead of diesel generators, the ship will receive an A rating between 2023 and 2026, a B rating in 2027, a C rating in 2028–2029, and an E rating in 2030. On the other hand, if hydrogen fuel cells are used, the ship will always remain at an A rating between 2023 and 2030. The capital expenditure (CAPEX) and operational expenditure (OPEX) of the fuel cell system are USD 1,305,720 and USD 2,470,320, respectively, for a 15-year lifetime, and the hydrogen fuel expenses are competitive at USD 260,981, while marine diesel oil (MDO) fuel expenses are USD 206,435.

Use of biofuels in marine diesel engines for sustainable and safe maritime transport

The article presents results of research on the use of fuel mixtures, containing with biodiesel fuel. The research was carried out on specialized sea vessels with a deadweight of 10,820 tons and 29,420 tons, which made passages in the waters of South America and the Caribbean, as well as in the Sulphur Emission Control Areas of Northern Europe. The operation of the ship's power plants (main and auxiliary engines) was provided both on marine fuel of petroleum origin and on a fuel mixture that consisted of petroleum fuel and biodiesel fuel. The experiments were carried out on marine medium-speed diesel engines 5DC-17A Daihatsu Diesel, 16V32 Wärtsilä-Sulzer and Volvo Penta TWD1645GE. Various kinds of marine fuels and as biodiesel fuel Fatty Acid Methyl Esters B99.9 FAME and B99.6 FAME were used. The concentration of biodiesel fuel in the fuel mixture was 5–20 %. The environmental friendliness of the work of sea vessels was assessed by the value of the emission of nitrogen oxides, sulphur, and carbon. As a result of the research, a variant of adjusting the sea crossing was proposed to ensure the continuous operation of the ship's power plant using biodiesel fuel.

Optimization of Combustion Cycle Energy Efficiency and Exhaust Gas Emissions of Marine Dual-Fuel Engine by Intensifying Ammonia Injection

The capability of operational marine diesel engines to adapt to renewable and low-carbon fuels is considered one of the most influential methods for decarbonizing maritime transport. In the medium and long term, ammonia is positively valued among renewable and low-carbon fuels in the marine transport sector because its chemical elemental composition does not contain carbon atoms which lead to the formation of CO2 emissions during fuel combustion in the cylinder. However, there are number of problematic aspects to using ammonia in diesel engines (DE): in-tensive formation of GHG component N2O; formation of toxic NOx emissions; and unburnt toxic NH3 slip to the exhaust system. The aim of this research was to evaluate the changes in combustion cycle parameters and exhaust gas emissions of a medium-speed Wartsila 6L46 marine diesel engine operating with ammonia, while optimizing ammonia injection intensity within the limits of Pmax, Tmax, and minimal engine structural changes. The high-pressure dual-fuel (HPDF) injection strategy for the D5/A95 dual-fuel ratio (5% diesel and 95% ammonia by energy value) was investigated within the liquid ammonia injection pressure range of 500 to 2000 bar at the identified optimal injection phases (A −10° CAD and D −3° CAD TDC). Increasing ammonia injection pressure from 500 bar (corresponding to diesel injection pressure) in the range of 800–2000 bar determines the single-phase heat release characteristic (HRC). Combustion duration decreases from 90° crank angle degrees (CAD) at D100 to 20–30° CAD, while indicative thermal efficiency (ITE) increases by ~4.6%. The physical cyclic deNOx process of NOx reduction was identified, and its efficiency was evaluated in relation to ammonia injection pressure by relating the dynamics of NOx formation to local combustion temperature field structure. The optimal ammonia injection pressure was found to be 1000 bar, based on combustion cycle parameters (ITE, Pmax, and Tmax) and exhaust gas emissions (NOx, NH3, and GHG). GHG emissions in a CO2 equivalent were reduced by 24% when ammonia injection pressure was increased from 500 bar to 1000 bar. For comparison, GHG emissions were also reduced by 45%, compared to the diesel combustion cycle.

Thermodynamic Analysis and Economic Assessment of Organic Rankine Cycle Integrated with Thermoelectric Generator Onboard Container Ship

In July 2023, the International Maritime Organization (IMO) presented an updated strategy for decarbonizing maritime transport and achieving net-zero greenhouse gas emissions by 2050. It is therefore imperative to explore innovative solutions to achieve a blue economy and maximize energy efficiency on-board ships. For this reason, the current study aims to integrate the organic Rankine cycle (ORC) and thermoelectric generator (TEG) on board a container ship to generate electrical energy and reduce fuel consumption. The combined system will benefit from the waste heat of a marine diesel engine installed on board. The current study uses R245fa as the organic liquid and analyzes the effects of varying the evaporation pressure on the energetic and economic performance indicators by modeling the combined system in Engineering Equation Solver (EES) software. The results show that the energy efficiency of the ORC system increases from 12.3% at 3.5 bar to 17.3% at 8 bar. In comparison, the energy efficiency of the TEG unit is 6.9% at different evaporation pressures. In addition, the energy efficiency of the TEG-ORC system is 18.3% with an output of 1386 kW at 8 bar, which is an increase of 30.5% compared to the value at 3.5 bar. This generated power reduces fuel consumption by around 1580 ton/year. From an economic point of view, the energy production cost of the combined system is USD 618/kWh and USD 614/kWh at the lowest and maximum evaporation pressure, respectively. Fuel costs and CO2 tax expenditures could be reduced by up to USD 1.169 million/year and USD 0.47 million/year, respectively, through the combined TEG-ORC system.

Visualization on spray and flame characteristics of wall-impinging spray under marine diesel engine conditions

Due to the longer nozzle-to-wall distance, spray-wall interaction with only vapor fuel impinging on the wall occurs generally in large-bore marine diesel engines. The interaction between the vaporized spray and wall not only impacts the combustion process, heat transfer, but also may condense and dilute the oil film on the cylinder wall. However, different from the scenario involving both liquid and vapor impinging on the wall in direct injection vehicle engines, the unique characteristics of vaporized diesel spray impingement have not been addressed in detail. To address the behavior of vapor diesel impinging spray and its influence on subsequent combustion in marine diesel engines, a 0.3 mm diameter single-hole injector, commonly used in marine diesel engines with a bore diameter around 170 mm, was utilized. The inclination angle of the injector is 30° and a flat wall was positioned 40 mm below the nozzle tip to approximate the relative positioning of the piston to the injector when the spray impinges on the wall in the engine. The interactions between spray and wall were studied under both inert and reactive conditions by altering the ambient gas to N2 and air, respectively. Back-illumination imaging, schlieren, and natural luminosity imaging were applied to study the impacts of ambient pressure, ambient temperature, and injection pressure on the evolution of impinging spray and diesel combustion within an optically-accessible constant volume chamber. Specifically, to evaluate the impact of spray-wall interaction with only vapor diesel impinges on the wall, the impinging sprays were compared to free sprays under the same experimental conditions. It shows that the impinging spray has a similar development mechanism with the free jet, while due to the varying air–fuel mixing rates at ambient pressures of 1 MPa and 3 MPa, the fuel film height on the wall exhibits different trends along the wall. At an ambient pressure of 5 MPa, the ignition delay of vaporized impinging spray is 17.62 % longer than that of free jet, while exhibiting a notable reduction in the soot emissions. The average time-integrated natural luminosity for jet impingement is found to be 71.28 % lower compared to the free jet with the same conditions.

Study on the forming process of the cylinder wall fuel film and the piston top land ablation mechanism of a medium speed marine diesel engine under cold start condition

The study presents an explanation of the piston top land ablation mechanism in a specific type of marine medium-speed diesel engine, utilizing multi-dimensional Computational Fluid Dynamics (CFD) software. At present, there is a lack of research on the process analysis of fuel droplets attached to the cylinder wall at diesel engine cold start condition and the mechanism of piston top land ablation. The study results indicate that during low-speed cold start condition, a multitude of diesel droplets impact the wall, causing the combustion area concentrated near the wall of the combustion chamber. The last stage fuel spray droplets, driven by the vortex in the cylinder, adhere to the cylinder wall before evaporation during the post-combustion stage. After multi-cycle operation of the diesel engine under cold start condition, the mass of fuel film adhering to the cylinder wall and the cumulative fuel mass on the top of the gas ring increase. As the engine getting warm, higher cylinder wall temperature leads to rapid evaporation of the fuel film on the cylinder wall and the gas ring. Deflagration happens when the fuel vapor burns under high temperature and high-pressure condition, and subsequent pressure oscillation destroys the thermal boundary layer of the piston top land. Piston material ablation happens under high temperature and high-pressure shock.

Research on Mechanical Model and Torsional Stiffness Properties of Leaf Spring Torsional Vibration Dampers for Marine Diesel Engines

The torsional stiffness parameter significantly influences the natural frequency of a leaf spring torsional vibration damper and its proper match with a diesel engine, and the nonlinear characteristics of torsional stiffness avoid reduced reliability due to the excessive torsion angle of the damper. An efficient mechanical model for the damper with nonlinear characteristics is established by integrating the Euler–Bernoulli beam theory and accounting for the geometric nonlinearity of leaf spring deformation during operation. The model’s validity is confirmed through finite element analysis. This study then explores the influence of design parameters on the mechanical characteristics of the damper. The results reveal a gradual increase in the torsional stiffness of the damper with the expanding arc radius of the clamping groove. Simultaneously, the torsional stiffness curve exhibits more pronounced nonlinear characteristics. In contrast, an elongation of the leaf spring leads to a sharp decline in torsional stiffness, accompanied by a diminishing prominence of nonlinear traits. Thus, both the arc radius of the clamping groove and the spring length significantly impact the torsional stiffness and nonlinear features of the leaf spring torsional vibration damper. The nonlinear characteristics intensify with an enlarged arc radius of the clamping groove and a reduced leaf spring length. Additionally, the damper’s torsional stiffness is influenced by the leaf spring thickness and the red copper gasket length. Future damper designs should comprehensively consider these relevant parameters.

Structural optimization of S-CO2 Brayton cycle compressor impeller based on evolutionary algorithm

As the critical components for marine low-speed diesel engine flue gas waste heat recovery (WHR) supercritical carbon dioxide (S-CO2) Brayton cycle system, the structure of the compressor impeller is optimized by the evolutionary algorithm (EA) based on the co-simulation of the CAESES, ANSYS CFX and Opti Slang. The law of impeller pressure ratio, efficiency and power consumption in S-CO2 Brayton cycle (SCBC) as a function of rotational speed, inlet temperature, pressure and impeller structural parameters are revealed, and the method of improving SCBC efficiency for marine low-speed diesel engine flue gas waste heat recovery is studied. The optimized impeller structure is greatly enhanced in aerodynamic performance and safety, and the isentropic efficiency is increased by 2.54%, the pressure ratio is increased by 35.64%, and the temperature rise is increased by only 4.6%. A 100kW S-CO2 compression cycle test bench was set up to verify the simulation-optimized impeller results. The final results show that the optimized impeller structure, aerodynamic performance and safety are greatly improved. It provides theoretical support for selecting and optimising compressor impellers for marine low-speed diesel engine flue gas waste heat recovery S-CO2 Brayton cycle.

Research on identification of key processes in machining process based on PageRank algorithm

Aiming at the difficulty of quantitatively evaluating the critical processes in the manufacturing process of complex mechanical products, a critical process identification method based on the PageRank algorithm is proposed with the goal of identifying key processes in the machining process. Based on the complex network theory, the error transfer network model of the machining process is established in this paper. Adopting the actual machining process as the data set of the complex network, the weights of the machining feature nodes are calculated by the PageRank ranking algorithm, and the nodes are ranked according to the weight values to assess the influence and importance of the nodes in the network model. Finally, taking the connecting rod machining process of a medium-speed marine diesel engine as an example, the results show that the method can quickly and effectively identify the key processes in the machining process.

Matching analysis on flow limiting valve of marine diesel engine common rail system

The flow limiting valve (FLV) designed for the high pressure common rail fuel system (CRS) was designed, the simulation model of the FLV and electronic controlled injector is established and the injector’s model was verified by experiment data. Through simulation, the maximum cycle injection quantity (CIQ) and close flow quantity (CFQ) of the CRS matched with the FLV are verified, and the influence of key FLV’s parameters on the matching performance was analysed. The maximum CIQ is 722mm3 and the CFQ is 1194.2mm3, which can satisfy the technical requirements of the CRS under overload conditions. The closing lift and orifice diameter of the FLV has a significant impact on the CFQ, which should be carefully designed according to the technical requirements, and the dimensional tolerance and processing accuracy should be guaranteed in the production and assembly process to ensure the consistency of the CFQ.

Diesel engine quality abnormal patterns recognition based on feature fusion and adaptive decision fusion

The current assembly process of marine diesel engines is low in intelligence and the control chart pattern classifier with unstable performance, which makes it difficult to control and identify the quality control chart pattern. This paper proposes a new assembly quality control diagram recognition method based on an adaptive decision model to address these problems. Through characteristics and changes of the diesel engine assembly process analyses, the triangular norm is used to fuse the extracted shape features and statistical features to reduce the influence of data fluctuation and imbalance on pattern recognition. An adaptive decision fusion model of the assembly process is established by defining multiple weights with considering the complexity and uncontrollability of the diesel engine assembly process. Based on these, the fusion coefficients within the adaptive decision model are optimized by the Ant Lion Optimization algorithm (ALO) to improve the decision efficiency and classification precision. To validate the proposed model, diesel engine exhaust pressure is selected as a case for abnormal pattern recognition, and the ability of the model is discussed in terms of recognition accuracy and stability.

Utilization of hydrogen-diesel blends for the improvements of a dual-fuel engine based on the improved Taguchi methodology

A three-dimensional computational fluid dynamics model (CFD) of the diesel engine cylinder was developed using CONVERGE 3.0 software and a chemical reaction mechanism including 172 reactions and 62 components was developed using the CHEMKIN program. Then, the effects of nozzle diameter and spray cone angle on in-cylinder pressure, temperature, HC emission, NOx emission and soot emission of the hydrogen-diesel dual-fuel engine were investigated. Lastly, multi-objective optimization of HES, CR, nozzle diameter and spray cone angle were also carried out using Taguchi methodology. Analysis of variance and signal-to-noise ratio were performed using Minitab software. The results showed that higher in-cylinder pressure, temperature and NOx emission could be obtained with the decreasing nozzle diameters. But HC and soot emissions showed the opposite trend. Using the smaller spray cone angle was more favorable for in-cylinder pressure, temperature, HC, and NOx emissions. However, the small spray cone angle results in large amounts of soot emission. In addition, the factors that had the greatest impact on in-cylinder pressure, temperature, HC emission, and soot emission were all CR. And the factor that had the greatest impact on NOx emission was HES. This work provides a feasible technical approach to improve the marine diesel engine parameters.

The Application of Cryogenic Carbon Capture Technology on the Dual-Fuel Ship through the Utilisation of LNG Cold Potential

The International Maritime Organization (IMO) has set targets to reduce carbon emissions from shipping by 40% by 2030 (IMO2030) and 70% by 2040 (IMO2050). Within the framework of decarbonising the shipping industry, liquefied natural gas (LNG) fuel and carbon capture technologies are envisioned as a transitional option toward a pathway for clean energy fuels. The aim of the complex experimental and computational studies performed was to evaluate the CO2 capture potential through the utilisation of LNG cold potential on the FSR-type vessel within a dual-fuel propulsion system. Based on the experimental studies focused on actual FSRU-type vessel performance, the energy efficiency indicators of the heat exchanging machinery were determined to fluctuate at a 0.78–0.99 ratio. The data obtained were used to perform an algorithm-based systematic comparison of energy balances between LNG regasification and fuel combustion cycles on an FSRU-type vessel. In the due course of research, it was determined that LNG fuel combustion requires 18,254 kJ/kg energy to separate and capture CO2 in the liquid phase to form exhaust gas; meanwhile, low sulfur marine diesel oil (LSMDO) requires 13,889 kJ/kg of energy. According to the performed calculations, the regasification of 1 kg LNG requires 1018 kJ/kg energy, achieving a cryogenic carbon capture ratio of 5–6% using LNG as a fuel and 7–8% using LSMDO as a fuel. The field of carbon capture in the maritime industry is currently in its pioneering stage, and the results achieved through research establish an informative foundation that is crucial for the constructive development and practical implementation of cryogenic carbon capture technology on dual-fuel ships.

Technical–Economic Analysis for Ammonia Ocean Transportation Using an Ammonia-Fueled Carrier

This study performed a technical–economic analysis for ship-based ammonia transportation to investigate the feasibility of international ammonia transportation. Ammonia is considered to be a vital hydrogen carrier, so the international trade in ammonia by ship will considerably increase in the future. This study proposed three scenarios for transporting ammonia from the USA, Saudi Arabia, and Australia to South Korea and employed an 84,000 m3 class ammonia carrier. Not only traditional very low sulfur fuel oil (VLSFO)/marine diesel oil (MDO) but also LNG and ammonia fuels were considered as propulsion and power generation fuels in the carrier. A life-cycle cost (LCC) model consisting of capital expenditure (CAPEX) and operational expenditure (OPEX) was employed for the cost estimation. The results showed that the transportation costs depend on the distance. The unit transportation cost from the USA to South Korea was approximately three times higher than that of Australia to South Korea. Ammonia fuel yielded the highest costs among the fuels investigated (VLSFO/MGO, LNG, and ammonia). When using ammonia fuel, the unit transportation cost was approximately twice that when using VLSFO/MDO. The fuel costs occupied the largest portion of the LCC. The unit transportation costs from Australia to South Korea were 23.6 USD/ton-NH3 for the LVSFO/MDO fuel case, 31.6 USD/ton-NH3 for the LNG fuel case, and 42.9 USD/ton-NH3 for the ammonia fuel case. This study also conducted a sensitivity analysis to investigate the influence of assumptions, including assumed parameters.

0D Model for the Comparative Analysis of Hydrogen Carriers in Ship’s Integrated Energy Systems

Hydrogen carriers are attractive alternative fuels for the shipping sectors. They are zero-emission, have high energy densities, and are safe, available, and easy to handle. Sodium borohydride, potassium borohydride, dibenzyltoluene, n-ethylcarbazole, and ammoniaborane are interesting hydrogen carriers, with high theoretical energy densities. The exact energy density of these hydrogen carriers depends on the integration of heat and mass with the energy converters. This combination defines the energy efficiency and, thus, the energy density of the system. Using a 0D model, we combined the five carriers with two types of fuel cells (PEM and SOFC), an internal combustion engine and a gas turbine. This resulted in 20 combinations. Despite the limitations of the 0D model and the occasional difficulty of validating input values, this model still produces exciting findings, which are valuable for further research. For the dehydrogenation of both dibenzyltoluene and n-ethylcarbazole, an external hydrogen burner is required if no waste heat resources from the integrated system are available. For the borohydrides, on the other hand, energy integration is essential for reducing cooling power. Dehydrogenation produces substantial energy, but only a fraction of this energy can be used for internal preheating. Dehydrogenation of ammoniaborane produces less energy. Among all hydrogen carriers, both ammoniaborane and sodium borohydride provide energy densities comparable to that of marine diesel oil. In particular, ammoniaborane possesses a remarkably high energy density. Thus, we conclude, that hydrogen carriers are attractive alternative fuels that deserve more attention, including their potential performance for hydrogen imports.

Cam Profile Design of Low-Speed Marine Diesel Engine Based on the Grey Theory

The camshaft profile is one of the important parameters of the engine, the reasonableness or otherwise of its design directly influences the engine’s power output, fuel consumption, emissions, noise and reliability. However, most existing cam profile optimization designs are based on the basic software operation, profile parameter selection and tuning lack a scientific theoretical basis. In order to address this issue, this study establishes a single valve kinematic model of the gas delivery mechanism of diesel engines by using the AVL-EXCITE Timing Drive, and performs a model-based multinomial kinematic acceleration cam profile design. Subsequently, an orthogonal design method is employed to obtain the parameter combinations that can satisfy the dynamic requirements. The research investigates the influence of cam profile design parameters (C 4, p, q, r, and s) on valve fullness, maximum jerk, cam contact stress, and valve seating force through a systematic study. Lastly, based on the grey correlation theory, a thorough analysis of the performance indices of cams with different profile parameter combinations is conducted. The optimization problem of the profile parameters with multiple performance indicators is transformed into a single-objective grey relational optimization problem, resulting in the optimal cam profile parameter combination of C4 =0.1, p=14, q=20, r=28 and s=36. The optimal method proposed in the paper is straightforward to implement and is applicable to the optimum design of cam profiles of the engine, which is of great importance for the optimal design of cam fabrication processes.

Research on combustion process optimization of marine diesel engines based on dual-injector system

Marine diesel engines are widely used with their strong power and mature technology. However, in recent years, the emphasis on environmental protection has made combustion pollutants the focus of attention, and the new regulations of the International Maritime Organization (IMO) and various countries have put forward new requirements and challenges for diesel engine combustion and emission performance. Due to the large size and large amount of circulating fuel injection, the incomplete mixing of fuel in the cylinder and the local violent combustion of high-power medium-speed marine diesel engines are important reasons for low thermal efficiency and high pollutant emissions. To achieve efficient and clean combustion of fuel in the cylinder, a dual-injector combustion system is designed on a dual-fuel engine basis, aiming to add a micro-injection before the central injection and provide positive in-cylinder flow and hot atmosphere for the atomized combustion of the central-injection fuel, so that the combustion in the cylinder is reasonably arranged, the thermal efficiency is improved and NOx emissions are reduced. The 3D simulation model was established by CFD software CONVERGE, and the physical model was calibrated according to the data of the pure diesel mode of the dual-fuel engine, and the influence of the small pilot-injection fuel volume on the development of spray and combustion in the cylinder at high and low load was analyzed. It was found that the small pilot-injection fuel volume at a high load had little effect on the atomization evaporation of the main-injection fuel and the hot atmosphere in the cylinder, so the improvement effect of combustion quality was not obvious, while the pilot-injection volume with the same pilot-injection capacity as high load relatively accounted for a large proportion at the low load with a small cycle injection volume. Without changing the injector specification settings of the original dual-fuel engine, the thermal efficiency was increased by 6.13% and the NOx generation was reduced by 22.42% by optimizing the injection timing, injection duration, and injection amount.

Diesel Substitution with Hydrogen for Marine Engines

Zero-carbon fuels are expected to catalyse the decarbonisation of the maritime industry, with hydrogen being considered a long-term solution. This study aimed to investigate the feasibility of using hydrogen as a secondary fuel in marine diesel engines. A marine four-stroke engine with a nominal power output of 10.5 MW at 500 rpm was investigated, whereas the hydrogen injection at the engine port was considered. A CFD model was set up in CONVERGE for both diesel and the diesel-hydrogen operating modes to investigate the effects of 20% hydrogen fuel fraction (by energy) on engine performance, emissions, and combustion characteristics. This model was validated against experimental data for the diesel operating mode. Based on a parametric study, the mesh characteristics were selected to compromise between the prediction error and the computational effort. The impact of 20% hydrogen energy fraction on the heat release rate (HRR) and NOx emissions is comparing with the diesel mode. The results demonstrate that despite the reduction in carbon emissions when using hydrogen, the NOx emissions increase by 2.5 times, whereas the lower compression ratio allows for engine free-knock operation. This study contributes to the identification of efficient and reliable combustion conditions for diesel-hydrogen dual-fuel marine engines.

Design, Analysis and Optimization of Fin-and-Tube Type Heat Exchanger in Marine Diesel Engine

Despite diesel engine technology seems close to be ending with decrease of electrical vehicles, it still has potential in marine, heavy-duty, and industrial areas. Marine diesel engines are frequently encountered in yachts, towing boats, and sailing boats. The cooling fluid is sea water in marine engines. The engine coolant water is cooled by shell and tube heat exchangers. Charge air is cooled by fin-and-tube type heat exchangers. In this study, fin-and-tube type heat exchanger’s design and flow analysis were investigated for the prototype six-cylinder inline engine. Heat exchanger’s header geometry was optimized to increase heat transfer, and an acceptable header design was decided upon with the analysis results.

Economic and environmental comparison between diesel-electric and mechanical propulsion plants for a small cruise ship

The paper reports an economic and environmental comparison between diesel-electric and mechanical propulsion plants, employed as an alternative to the other one, to the propulsion of a small cruise ship, also described in a previously authors article. The plants prime mover are two versions of the Rolls-Royce Bergen marine diesel engines, employed one as an alternative to the other in all the considered propulsion plants. The engines are characterized by similar rated power but with different power lint curves and specific fuel contours trend in the operating diagram. The diesel-electric propulsion plants are simulated considering the diesel generators working in both constant and variable speed. The economic and environmental (by EEDI and CII index) comparison results, between the considered ship propulsion plants, are presented in tabular and graphical form and commented.