Overall scheme design of a closed solid oxide fuel cell hybrid engine for ships

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A scheme of compact closed solid oxide fuel cell hybrid engines for ship power and propulsion on ships is proposed. A zero-emission closed engine at the effective equivalence ratio of 1 is achieved by recirculating water and fuelling by liquid hydrocarbon fuel and oxygen. The adiabatic pure oxygen reforming temperature of the reformer is higher than the specified anode inlet temperature. A turbine is placed in front of the solid oxide fuel cell anode. Detailed potential distributions are considered using a two-dimensional solid oxide fuel cell model, and thermodynamic models of the hybrid engine are built. The performance of the reformer is more sensitive to the oxygen-carbon ratio rather than the steam-carbon ratio, which leads to a huge change of the pressure ratio of the turbine. Therefore, the power ratios of turbines and SOFC are also affected by the oxygen and steam carbon ratio and excess oxygen coefficient. The optimized power ratio is 1.02–1.13, which results in a significant change in the efficiency of the engine. Under the specified operating conditions, the engine can achieve a high efficiency of 67 %. Under the off-design conditions, with the increase of the mass flow of fuel or the current density, the power of the engine can be changed from 20 % to 160 % of the designed power.