Fuel Cell APU for Silent Watch and Mild Electrification of a Medium Tactical Truck

This paper investigates the opportunities for improving truck fuel economy through the use of a Fuel Cell Auxiliary Power Unit (FC APU) for silent watch, as well as for powering electrified engine accessories during driving. The particular vehicle selected as the platform for this study is a prototype of the Family of Medium Tactical Vehicles (FMTV) capable of carrying a 5 ton payload. Peak stand-by power requirements for on-board power are determined from the projected future digitized battlefield vehicle requirements. Strategic selection of electrified engine accessories enables engine shutdowns when the vehicle is stopped, thus providing additional fuel savings. Proton Exchange Membrane (PEM) fuel cell is integrated with a partial oxidation reformer in order to allow the use of the same fuel (JP8) as for the propulsion diesel engine. The APU system is modeled and linked with the complete vehicle system simulation, and accessory duty cycles are derived for both silent watch and driving. The results indicate six-fold improvements of the silent watch fuel economy with the FC APU compared to main-engine idling, and relatively modest improvements from the mild electrification and FC APU use during the driving cycle. Combined fuel economy benefits calculated over the hypothetical daily military mission with a combined 10 hour highway/local/off-road driving and 10 hour silent watch are 20.1%.