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.

This paper describes a customized thruster for Autonomous Surface Vehicles (ASV). The thruster is a Pump-Jet Module (PJM), which has been expressly designed, modeled, constructed, and tested for small-/medium-sized ASVs that perform environmental monitoring in extremely shallow waters such as wetlands (rivers, lakes, swamps, marshes), where water depth is only a few centimeters. The PJM is a fully-electric propulsion unit with a 360-degree continuous steering capability. Its main advantage is that the unit is flush with the flat bottom of the vehicle. This makes the PJM suitable for operation in extremely shallow waters because the risk of damaging the thrusting unit in case of grounding is very limited. The PJM was produced using innovative materials, and the hydraulic components were all constructed using a 3D printer.

A turbocharged diesel engine numerical model, suitable for real-time ship manoeuvre simulation, is presented in this paper. While some engine components (mainly the turbocharger, intercooler and manifolds) are modelled by a filling and emptying approach, the cylinder simulation is based on a set of five-dimensional numerical matrices (each matrix is generated by means of a more traditional thermodynamic model based on in-cylinder actual cycle). The new cylinder calculation approach strongly reduces the engine transient computation time, making it possible to transform the simulation model into a real-time executable application. As a case study, the simulation methodology is applied to a high speed four stroke turbocharged marine diesel engine, whose design and off design running data are available from the technical sheet. In order to verify the suitability of the proposed model in real-time simulation applications, a yacht propulsion plant simulator is developed. Numerical results in ship acceleration and deceleration manoeuvres are shown, reducing the simulation running time of 99% in comparison with the corresponding in-cylinder actual cycle engine model.

The article shows the performance comparison between two marine engines, fuelled by natural gas and diesel oil, respectively, both belonging to the ‘Bergen’ engine series of Rolls-Royce Marine, suitable as prime movers for ship propulsion. Two different simulation codes, one for each engine, validated by means of geometrical and performance data provided by the manufacturer, 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 of the two types of engines. The reasons are investigated through a specific thermodynamic analysis, aimed to explain such differences, in terms of efficiency and emissions (particularly carbon dioxide), when varying the working conditions. 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. In addition, a study of the different modes of combustion is developed to explain the major differences found in the emissions of nitrogen oxides.

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.

In the last year, the Department of Naval Architecture and Marine Engineering of Genoa University (now Department of Naval Architecture, Marine Technology and Electrical Engineering) collaborated to the design of the propulsion automation of two different naval vessels; within these projects the authors developed different ship propulsion simulators used to design and test the propulsion control schemes. In these time-domain simulators, each propulsion component is represented by a specific mathematical model, mainly based on algebraic and differential equations. One of the key aspects of the propulsion simulation is the engine dynamics. This problem in principle can be dealt with models based on thermodynamic principles, which are able to represent in detail the behaviour of many variables of interest (engine power and speed, air and gas pressures, temperatures, stresses, etc.). However, thermodynamic models are often characterized by a long computation-time and moreover their development usually requires the knowledge of specific engine information not always available. It is generally preferable to adopt simpler simulation models, for the development of which, very few kinds of information are necessary. In fact, for the rapid prototyping of control schemes, it is generally more important to model the whole plant (in a relatively coarse way) rather than the detailed model of some components. This paper deals with simple mathematical methods, able to represent the engine power or torque only, but they can be suitably applied to many types of marine engines in a straightforward way. The proposed simulation approaches derived from the authors’ experience, gained during their activity in the marine simulation field, and they are particularly suitable for a fast prototyping of the marine propulsion control systems. The validation process of these particular models, regarding a Diesel engine, a marine gas turbine and an electric motor, is illustrated based on the sea trials data and engine manufacturers’ data. Keywords: Dynamic simulation; marine engines performance; gas turbine; propulsion control. doi: http://dx.doi.org/10.3329/jname.v8i2.7366 Journal of Naval Architecture and Marine Engineering 8(2011) 129-147