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The piston ring and cylinder liner (PRCL) system in larger-bore low-speed marine engines frequently experiences scuffing failures, which significantly decrease the engine reliability. To understand this failure mechanism, a scuffing failure model subjected to the PRCL system was developed considering multidisciplinary coupling effects that integrate asperity contact, hydrodynamic lubrication, tribochemistry reactions, thermal effects, friction, and surface wear. The impacts of large-scale deformation and gas-combustion mode on the scuffing performances of the PRCL system were examined. The key findings indicate that the larger-scale liner deformation can markedly reduce oil film thickness and exacerbate local asperity contact, influencing the evolution of the tribofilm by increasing the removal process. Under gas-combustion mode, the oil film thickness is even lower, and the asperity contact pressure further increases due to a more starved lubrication state and higher combustion temperature. This leads to tribofilm breakdown and severe wear near the ring opening area, which are aligning with the full-scale experimental results with scuffing failure. [ABSTRACT FROM AUTHOR]

The effects of heavy fuel oil and biodiesel blends on engine combustion and emissions were studied in a marine two-stroke diesel engine. The engine was operated under propeller conditions using five different fuels with biodiesel blends of 10% (B10), 30% (B30), 50% (B50), and sulphur contents of 0.467% low sulphur fuel oil (LSFO) and 2.9% high sulphur fuel oil (HSFO). Tests have shown that using a biodiesel blend increases the engine fuel consumption due to its lower calorific value. Heavy fuel oil has a high Polycyclic aromatic hydrocarbons (PAH) content, which leads to higher exhaust temperatures due to severe afterburning in the engine. A comparison of engine soot emissions under different fuel conditions was carried out, and it was found that the oxygen content in biodiesel promoted the oxidation of soot particles during the combustion process, which reduced the soot emissions of biodiesel. Compared to HSFO, B10, B30, B50 and LSFO, the soot emission concentrations were reduced by 50.2%, 56.4%, 61% and 37.4%, respectively. In our experiments, the soot particles in the engine exhaust were sampled with a thermal float probe. Using Raman spectroscopy analysis, it was found that as the biodiesel ratio increased, the degree of carbonisation of the soot particles in the exhaust became less than that in the oxygenation process, resulting in a decrease in the degree of graphitisation.

Container ships represent the fastest growing segment of maritime transport. The need to reduce unit transportation costs and environmental impact has led to development of the most capacious ultra-large container ships operating on the world's major shipping routes. A representative database of ultra-large container ships was created and further subdivided according to the main technical parameters. Using a simple cubic regression model, based on the least squares method, an equation, compliant to the general propeller law, was developed to predict the propulsion power of ultra-large container ships as a function of their sailing speed. The results obtained using the developed equation should be sufficiently close to the results of the exact verification calculations at the technical design stage. Then this prediction would find application in the design of both main propulsion, as well as waste heat and cold recovery systems. [ABSTRACT FROM AUTHOR]

Container ships represent the fastest growing segment of maritime transport. The need to reduce unit transportation costs and environmental impact has led to development of the most capacious ultra-large container ships operating on the world's major shipping routes. A representative database of ultra-large container ships was created and further subdivided according to the main technical parameters. Using a simple cubic regression model, based on the least squares method, an equation, compliant to the general propeller law, was developed to predict the propulsion power of ultra-large container ships as a function of their sailing speed. The results obtained using the developed equation should be sufficiently close to the results of the exact verification calculations at the technical design stage. Then this prediction would find application in the design of both main propulsion, as well as waste heat and cold recovery systems.

Existing and future regulations on ship energy efficiency and methods for their improvement are presented in this work. The design and operational features of gas-fuelled low-speed main engines, liquefied natural gas (LNG) regasification conditions, and amount of waste cold are compared. Using a simple linear regression model based on the least squares method, formulae were developed to predict the amount of waste cold as a function of the brake power of gas-fuelled low-speed main engines operating under ISO ambient conditions in Tier III-compliant mode. A sufficiently accurate prediction of the waste cold amount at the initial design stage is feasible due to the formulae developed as part of this work. [ABSTRACT FROM AUTHOR]

Existing and future IMO restrictions on emission of harmful substances contained in exhaust gas have introduced an obligation to implement technical solutions to reduce NOX, SOX and CO2 emissions. Reduction in NOX and SOX emissions has been achieved by systems (i.e. SCR and EGR) ensuring Tier III-compliant exhaust gas composition. SCR and EGR systems have also affected the amount of exhaust gas waste heat. Therefore reduction in CO2 emissions has mostly been dependent on available amount of exhaust gas waste heat to produce electricity using waste heat recovery generator unit instead of medium-speed diesel generating set. Comparative analysis of amounts of exhaust gas waste heat in LNG and MGO modes under ISO ambient conditions has been carried out with particular emphasis on the impact of different variants of SCR and EGR systems. Formulae to estimate the amounts of exhaust gas waste heat have been determined using least squares method. [ABSTRACT FROM AUTHOR]

Due to environmental, energy, and operating cost constraints, the number of liquefied natural gas (LNG)-powered ships is increasing. To avoid decreasing the thermal efficiency of two-stroke, low-speed diesel engines, high-pressure gas injection is used. The specific energy consumption of a gas fuel compressor is around 0.35 kWh/kg, which has a negative impact on the efficiency of ship power plants. To reduce the primary energy consumption of a gas fuel supply system, waste heat recovery (WHR) technologies may be used. This study investigated whether WHR metal hydride technology was suitable for improving the efficiency of low-grade heat waste in marine diesel engines. The key factors of this technology were revealed, and the design scheme was described. Working fluids were also analyzed, and a mathematical model of a WHR metal hydride plant was developed, and the results were represented. The calculations showed that the above technology could increase the operating power of a propulsion plant by 5.7-6.2%. The results demonstrate the possibility of applying WHR metal hydride equipment for gas fuel compressor drives in LNG-powered ships. The novelty of this study lies in the investigation of metal hydride technology for application in the waste heat recovery systems of LNG-powered ships. [ABSTRACT FROM AUTHOR]

High-pressure direct-injection (HPDI) natural gas marine engines are widely used because of their higher thermal efficiency and lower emissions. The effects of different injection rate shapes on the combustion and emission characteristics were studied to explore the appropriate gas injection rate shapes for a low-speed HPDI natural gas marine engine. A single-cylinder model was established and the CFD model was validated against experimental data from the literature; then, the combustion and emission characteristics of five different injection rate shapes were analyzed. The results showed that the peak values of in-cylinder pressure and heat release rate profiles of the triangle shape were highest due to the highest maximum injection rate, which occurred in a phase close to the top dead center. The shorter combustion duration of the triangle shape led to higher indicated mean effective pressure (IMEP) and NOx emissions compared with other shapes. The higher initial injection rates of the rectangle and slope shapes had a negative effect on the ignition delay periods of pilot fuel, which resulted in lower in-cylinder temperature and NOx emissions. However, due to the lower in-cylinder temperature, the engine power output was also lower. Otherwise, soot, unburned hydrocarbon (UHC), and CO emissions and indicated specific fuel consumption (ISFC) increased for both rectangle and slope shapes. The trapezoid and wedge shapes achieved a good balance between fuel consumption and emissions.

Penetrating exhaust manifold systems are commonly used in low-speed two-stroke marine diesel engines owing to their potential for energy conservation. However, few studies in the literature have reported on this type of manifold system, and there are few guidelines for optimizing the configuration or predicting the performance via a mean-line model. This study investigates the loss characteristics and flow mechanism of the penetrating exhaust manifold of a low-speed two-stroke marine diesel engine using experimental and numerical methods. The loss is characterized by the entropy production, which indicates a decrease in the energy grade. The results show that the minimum loss can be achieved when the penetration depth and diffusion angle of the manifold are approximately 0.5 and 6°, respectively. Moreover, the loss coefficient is maximally reduced by 14.0 % with penetrating exhaust manifold. The flow field analysis shows that the trend of the flow loss is 'decrease-increase' owing to the interaction among three factors: the mixing loss due to the shearing of the injection flow with the main flow, the momentum loss due to the impingement on the bottom of the main pipe, and the separation loss in the branch pipe owing to the flow divergence. This investigation can provide guidance for the configuration optimization and loss modeling of the exhaust manifold for low-speed two-stroke marine engines. • Loss characteristics of penetrating exhaust manifold in low-speed engine is studied. • Loss performance of PEM shows 'decrease-increase' trend with change of key geometry. • 'V-shape' trend is due to trade-off among losses of mixing, impinging and separation. [ABSTRACT FROM AUTHOR]

High-pressure direct-injection (HPDI) natural gas marine engines are widely used because of their higher thermal efficiency and lower emissions. The effects of different injection rate shapes on the combustion and emission characteristics were studied to explore the appropriate gas injection rate shapes for a low-speed HPDI natural gas marine engine. A single-cylinder model was established and the CFD model was validated against experimental data from the literature; then, the combustion and emission characteristics of five different injection rate shapes were analyzed. The results showed that the peak values of in-cylinder pressure and heat release rate profiles of the triangle shape were highest due to the highest maximum injection rate, which occurred in a phase close to the top dead center. The shorter combustion duration of the triangle shape led to higher indicated mean effective pressure (IMEP) and NOx emissions compared with other shapes. The higher initial injection rates of the rectangle and slope shapes had a negative effect on the ignition delay periods of pilot fuel, which resulted in lower in-cylinder temperature and NOx emissions. However, due to the lower in-cylinder temperature, the engine power output was also lower. Otherwise, soot, unburned hydrocarbon (UHC), and CO emissions and indicated specific fuel consumption (ISFC) increased for both rectangle and slope shapes. The trapezoid and wedge shapes achieved a good balance between fuel consumption and emissions. [ABSTRACT FROM AUTHOR]