Marine Engines Performance and Emissions [Editorial]

This article belongs to the Special Issue Marine Engines Performance and Emission

Hydrodynamics of Biomimetic Marine Propulsion and Trends in Computational Simulations

[Abstract] The aim of the present paper is to provide the state of the works in the field of hydrodynamics and computational simulations to analyze biomimetic marine propulsors. Over the last years, many researchers postulated that some fish movements are more efficient and maneuverable than traditional rotary propellers, and the most relevant marine propulsors which mimic fishes are shown in the present work. Taking into account the complexity and cost of some experimental setups, numerical models offer an efficient, cheap, and fast alternative tool to analyze biomimetic marine propulsors. Besides, numerical models provide information that cannot be obtained using experimental techniques. Since the literature about trends in computational simulations is still scarce, this paper also recalls the hydrodynamics of the swimming modes occurring in fish and summarizes the more relevant lines of investigation of computational models

Problemas resueltos de transmisión de calor

El presente texto tiene como objetivo servir de apoyo a las asignaturas Transmisión de Calor y Frío Industrial/Refrigeración, de los grados en Ingeniería Naval y Oceánica, Ingeniería Mecánica e Ingeniería en Tecnologías Industriales, que se imparten en la Escuela Politécnica Superior de la Universidade da Coruña. Su contenido también puede ser usado en asignaturas relacionadas con la transmisión de calor en otros grados y universidades. El libro consta básicamente de problemas resueltos procedentes del material utilizado para docencia, así como de exámenes realizados a lo largo de varios años. Esta colección de problemas aborda una visión global de la transmisión de calor, abarcando desde los fundamentos hasta los modos de transferencia de calor: conducción, convección y radiación, así como aplicaciones prácticas

Numerical Analysis of NOₓ Reduction Using Ammonia Injection and Comparison With Water Injection

[Abstract] This work analyzes NOₓ reduction in a marine diesel engine using ammonia injection directly into the cylinder and compares this procedure with water injection. A numerical model based on the so-called inert species method was applied. It was verified that ammonia injection can provide almost 80% NOₓ reduction for the conditions analyzed. Furthermore, it was found that the effectiveness of the chemical effect using ammonia is extremely dependent on the injection timing. The optimum NOₓ reduction was obtained when ammonia is injected during the expansion stroke, while the optimum injection timing using water is near top dead center. Chemical, thermal, and dilution effects of both ammonia and water injection were compared. The chemical effect was dominant in the case of ammonia injection. On the other hand, water injection reduces NOₓ through dilution and, more significantly, through a thermal effect

Optimization of a Multiple Injection System in a Marine Diesel Engine through a Multiple-Criteria Decision-Making Approach

[Abstract] In this work, a numerical model was developed to analyze the performance and emissions of a marine diesel engine, the Wärtsilä 6L 46. This model was validated using experimental measurements and was employed to analyze several pre-injection parameters such as pre-injection rate, duration, and starting instant. The modification of these parameters may lead to opposite effects on consumption and/or emissions of nitrogen oxides (NOₓ), carbon monoxide (CO), and hydrocarbons (HC). According to this, the main goal of the present work is to employ a multiple-criteria decision-making (MCDM) approach to characterize the most appropriate injection pattern. Since determining the criteria weights significantly influences the overall result of a MCDM problem, a subjective weighting method was compared with four objective weighting methods: entropy, CRITIC (CRiteria Importance Through Intercriteria Correlation), variance, and standard deviation. The results showed the importance of subjectivism over objectivism in MCDM analyses. The CRITIC, variance, and standard deviation methods assigned more importance to NOₓ emissions and provided similar results. Nevertheless, the entropy method assigned more importance to consumption and provided a different injection pattern

Application of the level set method to model the premixed combustion process in an otto two stroke engine

En este artículo se ha utilizado el método numérico conocido como level set para modelar el proceso de combustión en un motor Otto de dos tiempos. Se ha implementado el level set en un software libre de mecánica de fluidos computacional (CFD) basado en volúmenes finitos, el cual ha proporcionado los campos de presión y temperatura, así como la propagación del frente de llama. Con el fin de validar el modelo, los resultados obtenidos numéricamente se han comparado con datos experimentales, obteniendo una concordancia bastante satisfactoria. Asimismo, se ha comparado el método de level set con otro procedimiento numérico muy utilizado, mostrando la diferencia entre ambos resultados.In this paper, the numerical method level set has been used to model the combustion process in an Otto two-stroke engine. The level set has been implemented in a CFD (Computational Fluid Dynamics) software based in finite volumes. The pressure and temperature fields have been obtained, such as the propagation of the flame front. In order to validate this model, the numerically obtained results have been compared with experimental data, verifying a satisfactory concordance between both of them. Besides, the level set method has been compared with other numerical procedure, showing the difference between both results.Peer Reviewe

Analysis of the Pre-Injection System of a Marine Diesel Engine Through Multiple-Criteria Decision-Making and Artificial Neural Networks

[Abstract] The present work proposes several pre-injection patterns to reduce nitrogen oxides in the Wärtsilä 6L 46 marine engine. A numerical model was carried out to characterise the emissions and consumption of the engine. Several pre-injection quantities, durations, and starting instants were analysed. It was found that oxides of nitrogen can be noticeably reduced but at the expense of increasing consumption as well as other emissions such as carbon monoxide and hydrocarbons. According to this, a multiple-criteria decision-making (MCDM) model was established to select the most appropriate parameters. Besides, an artificial neural network (ANN) was developed to complement the results and analyse a huge quantity of alternatives. This hybrid MCDM-ANN methodology proposed in the present work constitutes a useful tool to design new marine engines

Vertical Axis Wind Turbines: Current Technologies and Future Trends

[Abstract] This paper, based on the pursuit of scientific articles published and recorded in the last five years (2010-2014) patents on VAWT technology, gives an image of the current situation of the treated technology. From data extracted we know:The different models that are working with different geometries, distinguishing between Savonius, Darrieus, hybrid of both (D+S), models dedicated to Offshore technology and what can be applied generally (D&S) on both types of VAWT (controllers, electric generators, materials ...). The main countries that research and develop VAWT technology, globally and at European level and the number of dedicated studies and patents each. Multiple applications that can be given in fields such as building, industrial environment, social areas, civil engineering and other more. Future trends for VAWT, which can be seen in our environment, both rural and urban, as has already happened with other renewable technologies for electricity production, as HAWT and photovoltaic (PV), becoming part of the mix of renewable energy technology and business network of the future, thereby contributing to the reduction of CO2 production and economic growt