• Energy Research

The paper reports a comparison, obtained by numerical simulation, between a natural gas spark-ignition engine and a liquid fuel compression-ignition engine, both belonging to the “Bergen” engine series of Rolls-Royce Marine, suitable as prime movers for ship propulsion. The delivered power of both supercharged engines is very similar (about 2 MW) at the same rotational speed. Two thermodynamic simulation codes, one for each engine, have been developed and validated by means of geometrical and performance data provided by the manufacturer. The analysis is carried out by comparing the respective real cycles, at the same working condition, and repeating the comparison for different engine delivered powers and rotational speeds. The comparison, extended to the whole working range of the engines, concerns mainly the following aspects: dimension and weight, overall efficiency, pollutant emissions. A specific thermodynamic analysis is developed to explain the differences between the two types of engines, in terms of efficiency and emissions.

Methanol as marine fuel represents one of the most cost-effective and practical solutions towards low-carbon shipping. Methanol fueled internal combustion engines have a high level of technological readiness and are already available on the market; however, technical data in terms of fuel consumption and emissions are not yet easily accessible. For this reason, the present study deals with the simulation of a virtual spark-ignition methanol engine, carried out in a Matlab-Simulink© R2023a environment to assess the CO2 emissions in several working conditions of a possible ship power system. The thermodynamic model of the methanol fueled engine is derived from a marine gas engine simulator, already validated by the authors in a previous work. This article presents the relevant modifications necessary to adapt the engine to the methanol fuel mode with regard to the different fuel characteristics. The simulation analysis compares the results of the virtual methanol engine with available data from a similar, existing gas engine, highlighting the differences in efficiency and carbon dioxide emissions.

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

This work aims at investigating the feasibility of COmbined Gas Electric and Steam (COGES) plants onboard Liquefied Natural Gas (LNG) fueled ships, by means of a novel, flexible tool. Firstly, the nominal operating conditions of 6 commercially available gas turbines (GTs) as well as their dynamic performance are simulated. Secondly, 6 different integrated COGES-reciprocating engine power plants are assembled and compared in terms of cogeneration efficiency within an optimized repowering study for the cruise-ferry ship GNV La Suprema. The optimization accounts for variable ship speed, season and GT control strategy for an overall number of 264 operating conditions considered. Thirdly, the time-dependent performance of the best COGES plant is assessed under actual navigation conditions for La Suprema. Overall, the results show the great potential of combining COGES plants with reciprocating engines for the marine sector. In particular, in the ship speed range centered around the actual cruise speed for La Suprema (i.e. 22 knots), all the COGES plants are able to cover the propulsion and hotel power demands more efficiently than reciprocating engines, with a 1–5 % benefit on cogeneration efficiency. Overall, a 51 % maximum cogeneration efficiency is found to be provided by COGES plants based on LM2500 and TITAN250 gas turbines.

Design and optimization of the propulsion system is a crucial task of the ship design. In fact the behaviour of the propulsion system is a key aspect of the global behaviour of a ship, mainly if the ship is a naval vessel. Simulation techniques can be very effective to predict the propulsion plant behaviour during normal working conditions as well as during critical situations. Numerical simulation gives the possibility to foresee, at design stage, the behaviour of the ship propulsion plant during manoeuvres and gives the designer the possibility to optimise the choice of the system parameters (choice of a suitable pitch/r.p.m. combination law, engine governor calibration, scantling of the shaft line) in order to prevent engine and mechanical overloads or faults. Moreover by simulation it is possible to study and optimise the machinery control system. The paper presents a comprehensive approach to simulate the propulsion system behaviour during transients and off design conditions to be used for the control system setting and overall ship propulsion plants study. The presented approach was successfully used for the design of the new high speed Italian Frigates FREMM class. This ships class has a new propulsion plant concept: the COmbined Diesel eLectric And Gas (CODLAG) type, with single gear and two shaft lines. The application presented in this paper concerns the design of the propulsion control system with a detailed simulation of the Gas Turbine Control System (TCS) and of the controllable pitch propeller system. A comparison between simulation transients results and reference data is reported in the paper.

In recent decades, the design of ship propulsion systems has been focusing on energy efficiency and low pollutant emissions. In this framework, diesel–electric propulsion has become a standard for many ship types and has proven its worth for flexible propulsion design and management. This paper presents an approach to the optimal design of diesel–electric propulsion systems, minimising the fuel consumption while meeting the power and speed requirements. A genetic algorithm performs the optimisation, used to determine the number and type of engines installed on-board and the engines’ design speed and power, selecting within a dataset of four-stroke diesel engines. The same algorithm is then adapted and applied to determine the optimal load sharing strategy in off-design conditions, taking advantage of the high flexibility of the diesel–electric propulsion plants. In order to apply the algorithm, the propulsion layout design is formulated as an optimisation problem, translating the system requirements into a cost function and a set of linear and non-linear constraints. Eventually, the method is applied to a case study vessel: first, the optimal diesel–electric propulsion plants are determined, then the optimal off-design load sharing and working conditions are computed. AC and DC network solutions are compared and critically discussed in both design and off-design conditions.

Currently the increase in fuel costs and the need to reduce Carbon Dioxide (CO2) emissions have encouraged the search for even more efficient solutions to be adopted in energy conversion systems for ship installations. These systems generally include thermal prime movers consisting mainly of two-stroke or four-stroke diesel engines, a waste heat recovery (WHR) plant, a steam turbine and possibly a gas turbine, as well as electric machinery. These components may be used in various ways and through different plant configurations, whose optimization is under investigation by researchers and diesel engine manufacturers. In this paper four schemes of ship propulsion plants, using a two-stroke diesel engine equipped with waste heat recovery system are presented, analysed and compared by simulation. Some of the considered layouts can include also an electric motor to support the main engine in providing power to the propeller. On the other hand the electric power can be generated from both the diesel generators ...