Fuel Cells for Micro Air Vehicles

1
Fuel Cells for Micro Air Vehicles

• James C. Kellogg, Lesli Monforton, Danielle
  White, and Michael Vick
• Tactical Electronic Warfare Division
• Karen Swider Lyons and Peter Bouwman
• Chemistry Division
• Naval Research Laboratory, Washington DC
• Joint Service Power Expo, Tampa FL 5May2005

2

• Demonstrate a Fuel Cell powered UAV
• Goal 4 to 6 Hours of flight
• Solution Hydrogen fuel cell (PEM)

• Potential Value
• Demonstrate fuel cells as a practical power
  source for a small UAVs
• Two to ten-fold energy increase over batteries

Polymer fuel cell Protonex Technology Corp

• Key issues
• Fuel
• Components selection
• System design
• System integration

Successful Autonomous Vehicles BUILD THE VEHICLE
AROUND THE POWER SOURCE
Sail plane with fuselage modified to house
hydrogen tank
3
Propulsion and power budget considered in design
Weight budgets for 20 min flight
The emergence of mini UAVs for military
applications Montgomery and Coffey, Defense
Horizons, Dec. 2002
4
Dragon Eye UAV

• Dragon Eye -
• 8 LiSO2 D-cells - 680 g
• Cruise at 110 W, climb at 300 W
• Power (160 W/kg)
• Rated for 45 min flight
• DISADVANTAGES of battery power source
• Limited energy (200 Wh/kg) 680 g 136 Wh
• Rarely full use of energy (throw out after 20
  min)
• Primary battery and per replacement
• ADVANTAGES
• Silent
• Low heat signature
• Attitude insensitive

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Fuel source OPTION 1 hydrogen gas

• Compressed hydrogen gas
• Up to 10,000 psi in large bottles
• Less pressure and Hydrogen in smaller bottles
  (larger surface area to volume)
• ADVANTAGES
• Responds immediately to change in load
• Easy to handle/recharge in lab environment
• No waste produced (only H2O)
• DISDAVANTAGES
• Difficult logistics (supplying hydrogen to remote
  locations)
• Safety

Paintball canister 0.7 kg and 4500 psi for
365 0.94 kg with fill valve and
regulators Specialty tanks designed for NASA may
be needed for lower weight/higher pressure
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Fuel Source OPTION 2 Chemical hydride

• LiAlH4 2 H2O --gt LiAlO2 4H2
• Theoretical 6943 Wh/kg
• Net system 3000 Wh/kg
• Working with Trulite Inc to use LiAlH system with
  recuperated product water from fuel cell
• ADVANTAGES
• High specific energy system
• Easy to work with in lab environment
• DISADVANTAGES
• Fuel system gains weight during flight
• Reaction creates additional thermal
• load
• Logistics issues with refueling in field
• Safety issue in humid environments
• Waste disposal

Fuel cell
air/H2O
H2
Chemical hydride
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Fuel Cell Powered Micro UAV
Step 1 Select an airframe

• Estimate weight and power of fuel cell system
• Test vehicle with batteries

Step 2 Integrate and test the fuel cell system
100W Protonex Stack
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Layout of fuel cell system

• Hydrogen system
• Storage Tank
• Regulator
• Pressure Relief
• Purge Valve
• Timer Circuit
• Air supply
• Pump
• Humidifier
• Cooling loop
• Pump
• Radiator

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System components
Radiator
Regulators
HP hydrogen tank (45ci)
Humidifier
Water pump
Timer Circuit
Valve
Air Pumps
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System Integration of Fuel Cell
Improved Fuel Cell system/parts, 115 watts on the
bench
Radiator
Fuel Cell
Water Pump
Humidifier
Hydrogen HP Tank
Flight weight 4.0 pounds
Air Pumps
Valve/Regulators
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Integration of parts into vehicle

• Vehicle center of gravity
• Set at 30 of chord
• Hydrogen tank heaviest part of system
• Pack air vehicle nose to offset weight of tank
  and regulator

• Component placement can affect fuel cell
  performance
• air flow
• water through humidifier

12
Weight breakdown of fuel cell system
Hydrogen tank, regulator, and air pumps dominate
system weight Hydrogen fuel 1
Weight distribution in Phase I demonstration of
PEM fuel cell system
13
Preparing the vehicle for flight

• Hydrogen cylinder filled
• Use cooler to prevent overheating
• Load tank into vehicle
• Systems check

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The Fuel Cell Flyer
Flight test, November 2004
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Total weight of vehicle

• Starting plan
• 3 lbs for air vehicle
• 3 lbs for fuel cell
• 1st generation vehicle
• 2.2 lbs for air vehicle/batteries
• (1 kg)
• 4.6 lbs for fuel cell system
• (2.1 kg)

• Approaches to lower weight of fuel cell system
• Decrease pressure drop through fuel cell
• Allows smaller air pump
• Consider MEMS-type air pump
• Use specialty hydrogen tank regulator -
  lighter weight
• Use chemical hydride system (properties TBD)

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Summary of power source specs

• Minimal signature from air pumps
• Cost
• 2500 fuel cell
• 365 tank
• 500 Electronics parts
• ?? Refueling
• Cycle life gt life of plane
• Logistics
• Fuel availability and safety

• Power 92 W
• Specific power 44 W/kg fuel cell
• 30 W/kg total vehicle
• Energy projected 276 Wh
• 3 h flight for 3000 psi H2
• 90 Wh/kg
• Environment
• Ambient humidity and temperature may affect
  performance
• No attitude sensitivity

Next steps - achieve higher specific power and
specific energy Add weight budget for mission
equipment (video, etc).
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Summary

• 8 h micro air vehicle flight
• State-of-art batteries are inadequate
• Fuel cells are a viable option for 8 to 12 h
  flights
• Building the vehicle around the power source is
  key to success
• Development team with expertise in fuel cells,
  air vehicles, and modeling
• Weight of fuel cell systems must be reduced for
  use in tactical vehicles
• Consider hydride fuels for PEMFCs
• Possibility of butane-fueled SOFCs

18
Acknowledgements

• Greg Ariff, Brian James
• Directed Technologies, Arlington VA
• William Skrivan, Paul Sabin, Paul Osenar
• Protonex Technology Corporation, Southboro, MA
• Timothy LaBreche, Aaron Crumm
• Adaptive Materials, Ann Arbor MI
• kellogg_at_suzie.nrl.navy.mil