Optimisation of a Hybrid-Parallel Power Train for a Aframax Tanker to Minimise Emissions in Every Operative Condition

The regulatory constraints imposed on the maritime sector regarding the complete elimination of greenhouse gas emissions by 2050 are driving extensive research into alternative fuels and renewable energy sources. In this context, biomethane might be a viable solution. Nevertheless, due to its higher price, it is even more important to enhance the energy efficiency of the ship’s power train to reduce consumption and minimize pollutant emissions during operation. Considering a hybrid-parallel power train, many possible configurations exist in terms of running internal-combustion engines, power exchanged through shaft electric motor/generator and power to/from batteries, to provide a given propeller thrust and onboard electric load for auxiliaries, outfitting and accommodation. This study proposes a method for the optimization of a ship’s power train of a biomethane-fuelled Aframax tanker with two propulsion four-stroke dual-fuel engines, a Controllable Pitch Propeller (CPP), two shaft motors/generators, one genset and an energy storage unit. Given each couple of thrust required by the ship and electric load and considering the engines’ specific fuel consumption curves and their limit, the study aims to determine the optimal combination of propeller pitch and power exchanged by each system component to minimise hourly fuel consumption. These results will be useful in giving guidance to the crew about how to manage the power train and to run probabilistic simulations of ship operation.