How to achieve energy efficiency and sustainability of large ships: a new tool to optimize the operation of on-board diesel generators

In this paper a novel dynamic simulation model for enhancing the sustainability of transportation systems equipped with diesel co-generators is presented. In each simulation time step of the carried out energy performance analyses, the best operation/combination of generators as well as their optimal part load ratio are determined with the aim to achieve the minimum fuel consumption. Input to the model are: size of each installed diesel generator; number of engines; required power profile; route scheduling and hourly weather data. The developed simulation model is implemented in TRNSYS environment. Here, a new in-house TRNSYS type written in Fortran is also included. With the presented approach - especially helpful for cruise ship designers, manufacturers and owners - new design criteria and useful technical results can be obtained. by determining an optimal sequence of generator operation is developed. To achieve this, the algorithm identifies the best operating sequence based on the power demand of the system, loading the most suitable number of engines and the appropriate load value to minimize fuel consumption for both the single engine and the entire sequence. During each simulation time step, the power required by the system is evaluated, and the algorithm determines the most suitable number and type of generators to satisfy the request while operating at the optimal load value to achieve minimum specific fuel consumption. The algorithm proposed is implemented in a dynamic simulation model, which is specifically designed for evaluating the energy performance of modern cruise ships. The energy system of modern cruise ships is equipped with two auxiliary boilers, five refrigeration units, and two different desalination systems, along with four diesel generators. To show the capability of the tool a novel case study is presented. It concerns on an existing cruise ship to be refurbished from the energy point of view. Here, four diesel generators are installed on-bord. The ship energy system includes five electric chillers, two auxiliary boilers, two reverse osmosis and two multi-stage flash desalination devices (driven by the diesel generators waste heat recoveries). Simulation results show remarkable energy savings obtained through the proposed optimization approach. Specifically, a maximum primary energy saving of about 15 GWh/y is obtained compared to the initial reference scenario. It corresponds to a fuel consumption reduction of 2.5 kt/y (-1.6 M$/y) and to an avoided CO2 emission of 8.0 kt/y.