Logistics and Capability Implications of a Bradley Fighting Vehicle with a Fuel Cell Auxiliary Power Unit

Modern military ground vehicles are dependent not only on armor and munitions, but also on their electronic equipment. Advances in battlefield sensing, targeting, and communications devices have resulted in military vehicles with a wide array of electrical and electronic loads requiring power. These vehicles are typically designed to supply this power via a main internal combustion engine outfitted with a generator. Batteries are also incorporated to allow power to be supplied for a limited time when the engine is off. It is desirable to use a subset of the battlefield electronics in the vehicle while the engine is off, in a mode called “silent watch.” Operating time in this mode is limited, however, by battery capacity unless an auxiliary power unit (APU) is used or the main engines are restarted. Integration of a solid oxide fuel cell (SOFC) auxiliary power unit into a military vehicle has the potential to greatly extend silent watch operating time and capabilities while significantly reducing fuel use.

In this paper the results of a study are presented which show the fuel usage and capability impacts of incorporating a fuel cell APU into the electrical system of a Bradley M2A3 Diesel Infantry Fighting Vehicle. Several APU sizes are presented with varying levels of electrical equipment and engine-off capability. Complete off-loading of engine-driven accessories is also studied as a scenario with the resulting impact on available engine power presented. The silent watch operating scenario shows an 86% reduction in fuel use. With fuel costing several hundred dollars per gallon as deployed on the battlefield, such a reduction is valuable. Furthermore, the SOFC APU offers 36 days of continuous silent watch using the same JP-8 fuel tank as the M2A3 without the need for a secondary fuel supply.