Comparison of lithium ion Batteries, hydrogen fueled combustion Engines, and a hydrogen fuel cell in powering a small Unmanned Aerial Vehicle

The relatively low energy density of lithium ion (Li-ion) batteries that power small Unmanned Aerial Vehicles (UAVs) limits their operating range. The use of hydrogen can provide a significant range improvement given its magnitude increase in mass and volume specific energy over Li-ion batteries. As a result, this effort investigates the potential of hydrogen-fueled power plants for small UAVs. Here, five powertrain options are simulated, namely Li-ion battery (LiNiCoAlO₂ and Li-air), internal combustion engine (ICE) with integrated generator, parallel hybrid ICE, free piston engine (FPE) with integrated linear generator, and proton exchange membrane fuel cell (PEMFC). The three major outcomes of this study include: (1) Though the performance characteristics of an ICE are superior to a FPE, the ICE has a relatively high manufacturing cost due to a more complex architecture, whereas a FPE can directly convert thermal energy to electricity; (2) PEMFCs can be readily integrated into an UAV since they provide electric power directly without a convoluted energy conversion system, reducing the overall weight of an UAV; and (3) Theoretically, the use of a Li-air battery pack would result in a longest flight time and simplest configuration; however, the necessary chemistry is still years away from practical implementation.