A comparative study on mean value modelling of two-stroke marine diesel engine

In the present paper, two mean value modelling approaches of varying complexity, capable of simulating two-stroke marine Diesel engines, are presented. Both approaches were implemented in the computational environment of MATLAB Simulink®. Simulation runs of transient operation cases of a large two-stroke marine Diesel engine were performed. The derived results were validated against previously published data are used for comparing the two modelling approaches and discussing the advantages and drawbacks of each

Modelling and parametric investigation of a large marine two-stroke dual fuel engine

This work deals with the modelling of a large marine two-stroke dual duel engine of the low gas pressure concept by using the GT-PowerTM software. Appropriate models were used to represent the engine processes including combustion, scavenging, heat transfer and friction whereas a knocking model was employed to characterise the engine unstable operation. The model was first validated against the manufacturer data and subsequently, the entire engine envelope in both operating modes was simulated. The derived results were used for analysing and discussing the engine performance and emissions as well as for comparing the two operating modes in terms of the turbocharger matching. In addition, parametric runs were performed and the results were used for identifying the settings that can further optimize the engine operation in the dual fuel mode in terms of CO2 and NOx emissions trade-off

Techno-economical analysis of single pressure exhaust gas waste heat recovery systems in marine propulsion plants

In this article, the waste heat recovery (WHR) installations used for the production of saturated steam and electric power for the cases of a two-stroke and a four-stroke engine propulsion plant of a typical merchant ship are investigated. The examined WHR system is considered to be of the single steam pressure type with an external heat exchanger for the heating of feed water entering into the boiler drum. The option of using the engine air cooler for heating the feed water was also examined. The WHR installation was modeled under steady-state conditions, and the derived WHR installation parameters for various engine loads are presented and analyzed. Furthermore, using the simulation results, the improvement of Energy Efficiency Design Index (EEDI) of the examined ship is calculated, and the impact of the WHR on the ship EEDI is discussed. In addition, following the technical evaluation of the alternative options for the ship propulsion plant, an economic study was performed for a typical ship voyage. The derived results were presented and discussed leading to conclusions for the most techno-economical propulsion system configuration

Analysis of two stroke marine diesel engine operation including turbocharger cut-out by using a zero-dimensional model

In this article, the operation of a large two-stroke marine diesel engine including various cases with turbocharger cut-out was thoroughly investigated by using a modular zero-dimensional engine model built in MATLAB/Simulink environment. The model was developed by using as a basis an in-house modular mean value engine model, in which the existing cylinder block was replaced by a more detailed one that is capable of representing the scavenging ports-cylinder-exhaust valve processes. Simulation of the engine operation at steady state conditions was performed and the derived engine performance parameters were compared with the respective values obtained by the engine shop trials. The investigation of engine operation under turbocharger cut-out conditions in the region from 10% to 50% load was carried out and the influence of turbocharger cut-out on engine performance including the in-cylinder parameters was comprehensively studied. The recommended schedule for the combination of the turbocharger cut-out and blower activation was discussed for the engine operation under part load conditions. Finally, the influence of engine operating strategies on the annual fuel savings, CO2 emissions reduction and blower operating hours for a Panamax container ship operating at slow steaming conditions is presented and discussed

Ship machinery condition monitoring using vibration data through supervised learning

This paper aims to present an integrated methodology for the monitoring of marine machinery using vibration data. Monitoring of machinery is a crucial aspect of maintenance optimisation that is required for the vessel operation to remain sustainable and profitable. The proposed methodology will train models using pre-classified (healthy/faulty) data and then classify new data points using the models developed. For this, vibration points are first acquired, appropriately processed and stored in a database. Specific features are then extracted from the data and stored. These data are then used to train supervised models pertinent to specific machinery components. Finally, new data are compared against the models developed in order to evaluate their condition. The above will provide a flexible but robust framework for the early detection of emerging machinery faults. This will lead to minimisation of ship downtime and increase of the ship’s operability and income through operational enhancement

Dynamic energy modelling for ship life-cycle performance assessment

This article summarises related work undertaken by the EC-funded Research Project TARGETS, which focuses on assessing energy efficiency by a direct approach. Energy flows onboard ships are considered in the time domain for complete ship energy systems simulation, allowing for interactions at system and component levels and accounting for different configurations, operating profiles, itineraries and environmental conditions. The approach and tools form the basis for life-cycle energy management considerations, addressing design, operation and retrofitting. To demonstrate the methodology leading to the evaluation of performance-based energy efficiency and its anticipated impact on ship design and operation, a case study for containership was carried out. Results are presented and discussed, demonstrating considerable advantage in adopting a more systematic and scientific approach to address Energy Efficiency of ships

Development of a combined mean value-zero dimensional model and application for a large marine four-stroke diesel engine simulation

In this article, a combined mean value–zero dimensional model is developed using a modular approach in the computational environment of Matlab/Simulink. According to that, only the closed cycle of one engine cylinder is modelled by following the zero-dimensional approach, whereas the cylinder open cycle as well as the other engine components are modelled according to the mean value concept. The proposed model combines the advantages of the mean value and zero-dimensional models allowing for the calculation of engine performance parameters including the in-cylinder ones in relatively short execution time and therefore, it can be used in cases where the mean value model exceeds its limitations. A large marine four-stroke Diesel engine steady state operation at constant speed was simulated and the results were validated against the engine shop trials data. The model provided results comparable to the respective ones obtained by using a mean value model. Then, a number of simulation runs were performed, so that the mapping of the brake specific fuel consumption for the whole operating envelope was derived. In addition, runs with varying turbocharger turbine geometric area were carried out and the influence of variable turbine geometry on the engine performance was evaluated. Finally, the developed model was used to investigated the propulsion system behaviour of a handymax size product carrier for constant and variable engine speed operation. The results are presented and discussed enlightening the most efficient strategies for the ship operation and quantifying the expected fuel savings

Investigation on gaseous fuels interchangeability with an extended zero-dimensional engine model

As the gaseous fuels interchangeability, which requires that the two gaseous fuels must be nearly identical in terms of their combustion characteristics and result in a similar engine performance, is important for internal combustion engines operation in cases of the fuel composition variation or the main fuel supply failure. In such cases, simulation tools of sufficient accuracy can be effectively employed in fuel interchangeability studies as well as for predicting the engine performance and emissions. In this study, a zero-dimensional diesel engine model is extended for simulating multi-fuel engines by considering the thermodynamic properties of the employed fuels. The model is verified against experimental data and subsequently employed to investigate the performance and knocking resistance of an SI engine operating with interchanged gaseous fuels mixtures. The derived results demonstrate that the Wobbe Index estimation is not sufficient for the characterisation of the engine performance and therefore simulation must be used for the accurate engine performance prediction with fuels interchangeability. The addition of either carbon dioxide or nitrogen results in reducing the knocking probability and retarding the knocking onset crank angle. It is inferred that the carbon dioxide addition is more effective than the nitrogen addition and concluded that the proposed model for multi-fuel engines provides results of sufficient accuracy to investigate the fuel interchangeability influence on the engine performance and knocking resistance

Investigation of ship cooling system operation for improving energy efficiency

The application of recently introduced IMO regulations for reduction of CO2 gaseous emissions as well as the initiatives for greener shipping, rendered the efforts for improving on-board energy systems performance to be of high priority. This study focuses on the investigation of the on-board operation of the combined sea/fresh water cooling system of a merchant ship. The detailed model of a cooling system is presented based on energy and mass conservation laws. The simulation input data includes the system geometry and arrangement, the operational characteristics of cooling pumps, the control scenarios for the system valves as well as data for calculating the pipes friction and minor losses coefficients, wherefrom the system performance parameters can be calculated. The cooling system energy consumption was estimated considering a typical annual ship operational profile. Two cases were investigated; first, a conventional case of controlling the sea water and fresh water temperatures by using three-way valves and, second, a more sophisticated case of installing variable speed motors for driving the system pumps. The obtained results are compared in terms of annual power consumption leading to conclusions about the system performance. The developed models can be used as an assessment tool for improving shipboard power demand early in the design stage and, also, during operation

A methodology for single turbocharger-marine engine matching

The turbocharger is an essential component for the propulsion and auxiliary engines of the modern ships’ power plants as it supplies the required air amount thus affecting the engine cylinders combustion process. In this respect, the matching of the marine engine with their turbocharging system is crucial for ensuring the engine efficiency as well as the propulsion systems response. In this paper, a new methodology consisting of three phases is proposed for facilitating the matching and selection process of a single turbocharging system with a two-stroke marine engine. The first phase included the estimation of the engine performance and the development of the compressor families’ databases by employing a single engine cylinder zero-dimensional model and a parametric compressor tool, respectively. The second phase involves the compressor maps-engine matching checking and the identification of the compressor maps that satisfy the set requirements, whereas the third phase includes the turbine matching along with the selection of the optimal compressor and turbine to minimise the specific engine fuel consumption for a selected propeller curve. The derived results indicate that the developed method can identify an appropriate turbocharger that is possible to improve the engine fuel consumption by 2−4%