Abstract
Nowadays, marine propulsion systems based on thermal machines that operate under the diesel cycle have positioned themselves as one of the main options for this type of applications. The main comparative advantages of diesel engines, compared to other propulsion systems based on thermal cycle engines, are the low specific fuel consumption of residual fuels, and their higher thermal efficiency. However, its main disadvantage lies in the emissions produced by the combustion of the residual fuels, such as carbon dioxide (CO2), sulfur oxide (SOx), and nitrogen oxide (NOx). These emissions are directly related to the operating conditions of the propulsion system. Over the last decade, the International Maritime Organization (IMO) has adopted a series of regulations to reduce CO2 emissions based on the introduction of an Energy Efficiency Design Index (EEDI) and an Energy Efficiency Operational Indicator (EEOI). In this context, adding a Shaft Generator (SG) to the propulsion system favoring lower EEDI and EEOI values. The present work proposes a selective control system and optimization scheme that allows operating the shaft generator in Power Take Off (PTO) or Power Take In (PTI) mode, ensuring that the main engine operates, always, at the optimum fuel efficiency point, thus ensuring minimum CO2 emissions.
Highlights
Even though marine propulsion systems have been in constant development since the 18th century, nowadays the most common system used on board large carriers, i.e., container ships and tankers, is a system considering a diesel engine as the prime mover
The Minimum Emissions Operating Point (MEOP) has been considered in this form because is a representation of the Specific Fuel oil Consumption (SFC), which is one of the factors to evaluate the amount of emissions generated by the engine when using the Efficiency Design Index (EEDI) and Efficiency Operational Indicator (EEOI)
Results of the fuel consumed by the engine when simulating the Power Take Off (PTO) and Power Take In (PTI) conditions are not yet significant in helping to reduce EEOI values at both operating regions, which means less operational CO2 emissions
Summary
Even though marine propulsion systems have been in constant development since the 18th century, nowadays the most common system used on board large carriers, i.e., container ships and tankers, is a system considering a diesel engine as the prime mover. The present work presents a marine diesel engine propulsion system with a direct driving shaft generator and a back to back converter based on the use of a selective control scheme This scheme enables for the diesel engine to operate at its optimum fuel oil consumption point, which has been renamed as its Minimum Emissions Operating Point (MEOP). The shaft generator, at PTO, generates enough power to turn-off the generator set of the ship These operational conditions have a repercussion on the EEOI, which is to be estimated and analyzed to prove the positive influence to lower the amount of emissions based on the reduction of the specific fuel oil consumption of the diesel engine. After EEOI results, the selective control scheme is going to be used to evaluate its influence over the EEDI of a new design looking for the development of an efficient propulsion system that ensures the compliance with the IMO regulations
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