Effects of upstream energy saving devices on engine operation

Abstract

Rising carbon emissions and the International Maritime Organisation (IMO) have put immense pressure on ship owners to make ships more efficient. One way to make ships more efficient is to install an energy saving device (ESD). ESDs are designed to perform at vessel’s design speed and design draft. Thus, there is abundant information available on how they perform at the design speed or speeds close to it. However, their performance in part-load conditions remains a question mark. Although these devices are used for ships having a high block coefficient and ships that sail at their design speed or close to it for the most part of their voyage, it is still important to assess their performance in part-load conditions and how they affect the engine operation.
The purpose of this thesis is to shed some light on the performance of three upstream ESDs on engine operation particularly, in part-load conditions. These three devices are Pre-duct, Pre-swirl stator and Mewis duct. Model tests and CFD self-propulsion simulations are used to assess their performance before implementing them. ESDs have been present since the first half of the 20th century. But despite that, their assumed working principle is still debatable. Performing simulations at all ship speeds is complex and time consuming. Hence, a new approach is proposed in this graduation report wherein a linear approach towards increase/decrease in specific propeller losses, influenced by the ESD, with respect to advance coefficient J is postulated. Advance coefficient is a dimensionless term defined as the ratio of the velocity of advance i.e the speed at which the water passes through the propeller disc, to the product of rotation rate and diameter of the propeller. The influence on losses is case dependent i.e depends on the type of ESD installed. The propeller is associated with three kinds of losses: axial, rotational and frictional losses. ESDs influence one or more of these losses to increase the propulsive efficiency. Therefore, the energy saving effect of these upstream ESDs increases linearly with advance coefficient. This new approach sheds some light on the performance of upstream ESDs i.e devices installed before the propeller, in part load conditions and helps in predicting their performance in low-medium speed range. This postulation is then implemented on a propeller loss diagram to make a simplistic model. This model is then implemented on the engine of a chemical tanker to assess the performance of the ESDs. The effect of these devices on engine operation is discussed and the model yields power savings for all the ESDs at design speed and speeds to close to it. However, it is found that power savings are marginal in part-load conditions even though the gain in propulsive efficiency is more or less the same at all speeds. This raises the question whether power savings in part-load condition even matter. A reduction in Energy Efficiency Design Index (EEDI) is also seen for the three ESDs. It is recommended to further study the postulation that the decrease or increase in losses associated with the propeller, influenced by these ESDs, varies linearly with advance coefficient.