Investigation of a Hybrid Powertrain Utilizing Solid Oxide Fuel Cells and Internal Combustion Engine for Unmanned Aerial Vehicles

Alexander Metcalf, Thomas S. Welles, Jeongmin Ahn

Research output: Chapter in Book/Entry/PoemConference contribution


This work investigates a combined internal combustion engine and solid oxide fuel cell (SOFC) hybrid powertrain for unmanned aerial vehicles (UAVs). UAVs are increasingly used in large agriculture for crop management and water resource visual inspection, and in militarized applications, as they allow for safer, unmanned reconnaissance missions. The limited flight time of UAVs, as a result of the traditional lithium polymer batteries used for power, has restricted the widespread implementation of the UAV technology. A hybrid power train, utilizing energy dense liquid fuel, provides the capability of powering a UAV for longer duration missions. The hybrid power train consists of a small internal combustion engine that acts as a partial oxidation fuel reformer, simultaneously producing mechanical shaft power. The 0.3 in3 piston engine is a typical air cooled, glow engine utilizing a 60/40 percent (by volume) mixture of methanol and nitromethane, respectively. The syngas generated by the combustion engine can then be utilized by a tubular SOFC stack to generate electrical energy for the UAV flight systems. The SOFC system operating on combustion exhaust from the engine produced a maximum of ~650 mW/cm2, while the engine was continually producing ~750 W of mechanical shaft power. In case of an engine failure, the liquid fuel may be directly utilized by the SOFC system to maintain power generation. Additionally, the engine may be manually shutdown to provide silent onboard power generation. In testing, a tubular SOFC provided with direct liquid 60/40 methanol/nitromethane fuel was capable of producing above 550 mW/cm2 for maximum power. The SOFC system was able to operate continuously under direct liquid fueling for 4 hours without degradation. Additional experimentation was performed to discern the nature of the combustion process as it leaves the SOFC, and to provide scientific backing to the exceptional performance of the 60/40 methanol/nitromethane fuel mixture. By method of gas chromatography and mass spectrometry (GC-MS), the combustion products exiting the SOFC were collected and analyzed with the goal of proving the 60/40 mixture is the ideal fuel source for this application. The power produced by the proposed hybrid powertrain is expected to be sufficient to power a up to a 25 kg gross takeoff weight UAV for long endurance missions lasting in the range of 200-500 % of current battery powered UAV flight duration.

Original languageEnglish (US)
Title of host publicationAIAA Propulsion and Energy Forum, 2021
PublisherAmerican Institute of Aeronautics and Astronautics Inc, AIAA
ISBN (Print)9781624106118
StatePublished - 2021
EventAIAA Propulsion and Energy Forum, 2021 - Virtual, Online
Duration: Aug 9 2021Aug 11 2021

Publication series

NameAIAA Propulsion and Energy Forum, 2021


ConferenceAIAA Propulsion and Energy Forum, 2021
CityVirtual, Online


  • Flame-assisted Fuel Cell (FFC)
  • Hybrid Power System
  • Solid Oxide Fuel Cell (SOFC)
  • Unmanned Aerial Vehicle (UAV)

ASJC Scopus subject areas

  • General Energy
  • Aerospace Engineering
  • Control and Systems Engineering
  • Electrical and Electronic Engineering
  • Mechanical Engineering


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