Design and optimization of the propulsion system is a crucial task of the ship design\ud process. The behaviour of the propulsion system, in transient conditions as well as in steady\ud state, is greatly affected by the capability of the control system to manage the available power\ud and to achieve the desired performance in the shortest time.\ud The selection of a proper control scheme is a trade-off between different and conflicting\ud needs. Two of the opposites are: increasing the ship operability by adding more functions and\ud more controls; and reducing the control system development and installation time and cost.\ud In this paper, the rapid prototyping and testing procedure for the development of the\ud propulsion controller of the new Italian aircraft carrier Cavour is presented, using real-time\ud hardware-in-the-loop (RT-HIL) simulation. The procedure is based on a wide use of simulation\ud technology. First, a complete dynamical model of the ship propulsion plant was developed.\ud Then, batch simulation was used to develop the best possible control scheme. Finally, RT-HIL\ud simulation was used to debug the real controller software and to tune the controller parameters\ud before sea trials.\ud The application of the procedure led to a significant reduction in the development phase of\ud the controller design. Furthermore, the adoption of the RT-HIL technology greatly reduced the\ud time spent to tune the control system during the ship delivery phase

Abstract:The paper presents the main results of a research project directed to the development of mathematical models for the design and simulation of combined Gas Turbine-Steam or Diesel-Steam plants for marine applications. The goal is to increase the energy conversion efficiency of both gas turbines and diesel engines, adopted in ship propulsion systems, by recovering part of the thermal energy contained in the exhaust gases through Waste Heat Recovery (WHR) dedicated installations. The developed models are used to identify the best configuration of the combined plants in order to optimize, for the different applications, the steam plant layout and the performance of WHR plant components. This research activity has allowed to obtain significant improvements in terms of energy conversion efficiency, but also on other important issues: dimensions and weights of the installations, ship load capacity, environmental compatibility, investment and operating costs. In particular, the main results of the present study can be summarized as follows: (a) the quantitative assessment of the advantages (and limits) deriving by the application of a Combined Gas And Steam (COGAS) propulsion system to a large container ship, in substitution of the traditional two-stroke diesel engine; (b) the proposal of optimized WHR propulsion and power systems for an oil tanker, for which a quantitative evaluation is given of the attainable advantages, in terms of fuel consumption and emissions reduction, in comparison with more traditional solutions.

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The article shows the performance comparison between two marine engines, fuelled by diesel oil and natural gas respectively. Two different simulation codes, each for engine type, have been developed to extend the comparison to the whole working area of the examined engines. Although the maximum continuous power is very similar (about 2 MW at the same rotational speed), some differences exist in size, efficiency and pollutant emissions. The reasons are investigated through a specific thermodynamic analysis, by comparing the respective real cycles at several power and revolution values. In detail, the two combustion modes are analysed to explain the main differences that are found mostly in nitrogen oxides emissions

In this article, some configurations of waste heat recovery systems are described, analysed and compared, in order to\ud find the optimal plant layout. Starting from the availability of performance data of a two-stroke diesel engine, adopted for\ud the propulsion plant of a crude oil tanker ship, the authors examined different solutions for the waste heat recovery\ud from the diesel engine exhaust gas ensuring the best fulfilment of the vessel needs in terms of mechanical, electric and\ud thermal energies. The considered waste heat recovery systems can adopt either steam turbine and gas turbine or simply\ud steam turbine for power generation. As regards the steam plant, two basic layouts are considered, optimized and compared:\ud the first plant scheme is a typical steam plant currently adopted for waste heat recovery purposes and the second\ud one is a solution proposed by the authors. Considering the different options, in this article, four different system layouts,\ud applied to the mentioned diesel engine, are singly optimized and compared between them in order to find the most suitable\ud plant and the steam cycle parameters that provide its best operation at the engine normal continuous rating. The\ud performance of the optimized waste heat recovery systems is evaluated also by comparing them under off-design engine\ud load conditions, in the engine power range between 50% and 100% of its maximum continuous rating

Abstract:The use of a computer simulator, previously developed and validated, applied to a four-stroke marine dual-fuel engine, has allowed the authors to present in this paper a solution to improve the overall efficiency of the engine by adopting a hybrid turbocharger. This component replaces the original one allowing, in addition to maintaining the previous usual functions, the production of electricity to satisfy part of the ship's electric load. In this study the application of the hybrid turbocharger concerns an engine powered by natural gas in particular. The turbocharger substitution involves a significant variation of the engine load governor operating mode. The improved engine characteristics that the hybrid turbocharger facilitates, compared to the original, are highlighted by the results reported in tabular and graphical form, for different engine loads and speeds.

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