The use of fuel cells to enhance the underwater performance of conventional diesel electric submarines

Abstract

Air Independent Propulsion (AIP) systems have the potential to improve the underwater performance of conventional diesel electric submarines and to reduce their vulnerability. Many different types of AIP systems are being considered, either for integration into new submarines or for retrofitting to existing submarines by the insertion of an additional section or ‘plug’. Based on a generic submarine, this paper presents conceptual designs for fuel cell-based AIP plugs that could be retrofitted to an ocean-going conventional submarine of about 3 000 t displacement. The designs are based on solid polymer electrolyte fuel cells that use hydrogen and oxygen as reactants to produce a nominal 100 MWh of electrical energy. Three hydrogen storage methods are considered: metal hydrides; liquid hydrogen, or hydrogen generated from the reforming of methanol. The metal hydride method is mass limited and requires a longer plug than the other two options. The liquid hydrogen and methanol reforming methods are both volume limited and the plug displacement is much greater than the system mass. To maintain neutral buoyancy, considerable ballast has to be added to the plug, or elsewhere in the submarine. Equipped with a 600 kW fuel cell, the generic submarine's maximum speed on fuel cell alone is about 8 knots. The submarine is much harder to detect, because, at speeds below 8 knots, it does not need to snorkel. With a nominal 100 MWh of electrical energy, the submarine's maximum underwater range is increased by a factor of almost five compared with the range of a single battery charge. The maximum endurance is about 14 days. AT speeds greater than the maximum possible with the fuel cell only, the range and endurance of the submarine is increased considerably when the fuel cell and battery are used together.