The shipping industry is facing increasing demands to reduce its environmental footprints. This has resulted in adoption of new and more environmental friendly power sources and fuels for on-board power generation. One of these novel power sources is the Solid Oxide Fuel Cell (SOFC) which has a great potential to act as a power source, thanks to its high efficiency and capability to handle a wide variety of fuel types. However, SOFCs suffer from low transient capabilities and therefore have never been considered to be used as the main power source for maritime applications. In this paper, novel component sizing, energy and power management approaches are proposed to enable the use of SOFCs as the main on-board power source for the first time in the literature and integrate them into the liquefied natural gas fueled Power and Propulsion System (PPS) of vessels. The proposed component sizing approach determines the power ratings of the on-board sources (SOFC, gas engine and battery) considering size and weight limits, while the energy and power management approaches guarantee an optimal power split between different power sources and PPS stability while looking after battery aging. The results indicate that the combined proposed optimization-based approaches can yield up to 53% CO₂ reduction and 21% higher fuel utilization efficiency compared to conventional diesel-electric vessels.

This paper investigates the effects of hybrid electric turbocharging on the total system efficiency, the transient loading capability and the operational range of maritime engines, including the effects of the air control valves (cylinder bypass & charge air blow-off valve). An existing and validated mean-value first principle engine model has been adapted to simulate the operating principle of a combustion engine with a hybrid electric turbocharger system. The simulation of power-take-off/in together with an excess air ratio control strategy is included by means of torque addition to/removal from the turbocharger shaft and limiting it with seven boundary controllers. The analysis of the simulation results illustrates a trade-off between the increase of the system efficiency on one side and the transient loading capability of the engine on the other side. With turbocompounding, the system efficiency can be increased at the expense of a deteriorated gas exchange process and increased thermal loading of the engine. And assisting the turbocharger for steady state operation leads to a smaller operating envelope due to the limitation of compressor surge. Combining turbocharger assistance, with either the cylinder bypass or the charge air blow-off valve to avoid compressor surge, results in a rise of the engine torque at a lower speed almost up to a constant engine torque. The system efficiency can be further improved for the low-speed region in case the turbocharger is assisted electrically in combination with the air control valves. The load step capability, parametrized by limiting the minimum excess air ratio during the load step event, proved to be dependent on the timing of the electrical support. It was found, that in order to improve the load step capability, it is necessary to start accelerating the turbocharger a few seconds before the load step occurs. The paper shows the effect of hybrid electric turbochargers on the engine characteristics to facilitate enhanced engine dynamics and improved engine torque at reduced engine speed.