Abstract
The work described below investigates the prospect of utilizing a two-stroke internal combustion engine and solid oxide fuel cell (SOFC) stack for hybrid power generation for an unmanned aerial vehicle (UAV). UAV technology is increasingly useful for large land and water management settings, such as agriculture. However, in their current state, small UAVs are limited by the lithium polymer batteries that commonly power them, which only provide power for short duration flights around 30 minutes. The proposed hybrid powertrain is capable of harnessing energy dense liquid hydrocarbon fuel, hence significantly increasing the flight endurance of UAVs. The 0.3 in3 piston engine is a typical air-cooled, glow plug ignited, two-stroke engine which acts as a partial oxidation fuel reformer, and a generator of mechanical shaft power. Additionally, a tubular SOFC stack can harness the syngas generated by the piston engine and produce electrical energy. From combustion simulation results, it was determined that a 60/40 percent (by volume) mixture of methanol and nitromethane, respectively, produced the largest quantity of total syngas. While fueling the SOFC with exhaust modeled after this fuel the SOFC generated a peak power density of ∼650 mW/cm2. The hybrid power system includes the added benefit in that it can be operated in an “engine out” scenario, where the SOFC stack is fed direct liquid fuel. Operating on liquid 60/40 methanol/nitromethane fuel, a tubular SOFC produced ∼580 mW/cm2 maximum power density.
