Hydrogen and fuel cell technology for aerospace applications

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Hydrogen and Fuel Cell Technology
for Aerospace Applications
CLEMENT
JESTIN

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The Hydrogen Revolution in the Skies
The usage of hydrogen as a fuel in place of fossil commodities has some challenges but its advantages
outweigh the disadvantages. The hydrogen has the highest energy per unit mass compared to any other fuel
obtained chemically. Its energy density is 2.5 times bigger than that of kerosene. Using hydrogen as an aviation
fuel would eliminate most of the GHG emissions including all carbon-based emissions, soot, and Sulphur oxides.
The main by-products of hydrogen in a combustion process are water vapor (H2O) and nitrogen oxides (NOX).
NOx emissions are associated with the formation of smog, acid rain and particulate matter. However, the
amounts of NOx emissions released from burning hydrogen are extremely low compared to those released when
burning kerosene.
SOURCE: Comprehensive investigation on hydrogen and fuel cell technology in the aviation and aerospace sectors - ScienceDirect

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Hydrogen can be combusted through modified gas-turbine engines or
converted into electrical power that complements the gas turbine via fuel cells.
The combination of both creates a highly efficient hybrid-electric propulsion
chain powered entirely by hydrogen.
AIRBUS’s ambition of bringing a zero-emission commercial aircraft to market by 2035
SOURCE: https://www.airbus.com/en/innovation/zero-emission/hydrogen/zeroe

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Hydrogen Fuel Cell for Aviation Applications
Hydrogen tank has only a 6% hydrogen storage weight fraction for hydrogen fuel cells, the energy density would be greater
than 1000 W-hr/kg.
For a successful development of fuel cell for an aircraft, the following factors should be considered:
 Weight reduction and reliability improvement of fuel cell components necessary for meeting aircraft requirements.
 Improvement of catalyst durability and reactor design to optimize hydrogen generation rate and to prevent borate clogging.
 Improvement of power density of
the fuel cell stack by a new design
or new materials for bipolar plates.
 Fast startup of the fuel cell system
and convenience of fuel recharge.
 Performance evaluation and
optimization of the fuel cell aircraft
under harsh operating
environments, such as midsummer,
midwinter, or rainy days
SOURCE: https://www.intelligent-energy.com/our-products/stationary-power/fuel-cells/

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HYDROGEN PRODUCTION METHODS
SOURCE: https://energyeducation.ca/encyclopedia/Types_of_hydrogen_fuel Comprehensive investigation on hydrogen and fuel cell technology in the aviation and aerospace sectors - ScienceDirect

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AIRCRAFTS POWERED BY HYDROGEN FUEL CELL
The main objective of the ENFICA-FC project is to
develop and validate the use of a fuel cell based power
system for propulsion of more/all electric aircraft.
The fuel cell system is installed in the light sport
aircraft RAPID 200 which was flight and performance
tested as a proof of functionality and future applicability
for inter city aircraft.
In order to achieve a flyable aircraft for the prescribed mission a peculiar architecture for the power
system was adopted. Relying solely on fuel cells for the entire mission, including take-off, leads to an
excessive weight due to the high amount of needed hydrogen or a excessive reduction of cruise time at
fixed hydrogen tank capacity; for this reason an hybrid battery/fuel cell system was chosen.
Expect for takeoff and landing, more than 50% of the
power is supplied by the fuel cell. The battery is used
only in the most demanding conditions.
Source: (PDF) ENFICA-FC: Design of transport aircraft powered by fuel cell & flight test of zero emission 2-seater aircraft powered by fuel cells fueled by hydrogen (researchgate.net)
Rapid 200 flight where the fuel cell is installed

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Some structural component had to be redesigned or introduced
in order to make the new layout possible. Engine mount was
carefully and heavily re-designed as support for many different
subsystems. A special lightweight support plate for hydrogen
tanks was designed.
Current fuel cell aircrafts can be classified by fuel cell types and
hydrogen storage methods. Polymer electrolyte membrane fuel
cells (PEMFC), which use hydrogen as the fuel, have been
widely used due to its low operating temperature and relatively
high power density.
Recently, solid oxide fuel cells (SOFC) were applied. An SOFC
uses a hydrocarbon fuel at high temperatures, producing a
power density higher than that of PEMFC.
Final lay-out configuration
Weights of subsystems
Source: (PDF) ENFICA-FC: Design of transport aircraft powered by fuel cell & flight test of zero emission 2-seater aircraft powered by fuel cells
fueled by hydrogen (researchgate.net)

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The fuel cell system (developed by IE), that is able to provide 20
kW on net unregulated power, consists of: ƒ
•Fuel Cell Stack & Electrochemical System ƒ
•Heat Exchanger System ƒ
•Air Delivery & Water recovery system ƒ
•Water Management Subsystem ƒ
•Electrical & Electronic Support System
•Control and Internal Battery Subsystem
ECSS - Electro-Chemical Sub System:
System consists of two separate fuel cell units. To provide a safe mounting system, the fuel cell stack is enclosed
in a lightweight structure that provide also safe ventilation of any hydrogen leak and electrical isolation. Stacks
are designed for a maximum current of 110A.
FUEL CELL SYSTEM
Fuel cell system assembled in the mock-up fuselage
ACSS - Air Compressors Sub System
The system is designed as two-stage centrifugal compressors in
series. It will bring the fresh air from engine cowling inlet and source
fuel cell stack with compressed air.
Ctrl SS - Control Sub System
This system comprises of FCS central communication and control module and Internal Battery Sub System (a
battery that is used to start-up the fuel cell).

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Installed heat exchanger and cyclone unit
HEXSS – Heat Exchanger Sub System
The heat exchanger assembly is situated in the front part of the
engine bay under the electric motor. The fresh air flows through the
engine cowling inlet and heat exchanger matrix, cools the waste
water-air mixture from fuel cell stacks and leaves the engine bay
through the outlet opening around the front gear housing. Cooled
waste water-air mixture comes to the cyclone where water is
separated from the air and directed back to the water tank to be re-
used.
WMSS – Water Management Sub System
It consists of water tank assembly situated in the right central wing
part leading edge and water pump, filter and flow meter situated in the
engine bay. The leading edge was originally used as fuel tank. It was
necessary to replace the fuel tanks with aerodynamic covers. The ribs
were positioned and designed to serve also as the supporting
structure for water tank hinges. The first prototype of the water tank is
showed. The actual tank can be showed as it’s directly integrated in
the wing leading edge aluminum sheet.
Water tank prototype

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Hydrogen Subsystem
The system comprises two Dynatek L026 tanks with
accessories (valves, sensors etc). Their capacity is 26 litres
each or 0.6 kg of hydrogen at 350 bar pressure. The whole
assembly is installed in the baggage compartment behind
the pilot. It is separated from cockpit by aluminum wall.
Hydrogen storage system
Battery Packs
Two packs of Li-Po batteries supply additional energy
necessary for take-off and climbing; the pack is able to deliver
20 kW for about 19 minutes. They are stored in two carbon
fiber containers (with glass/fiber covers) which are secured with
rails to the cabin floor at co-pilot’s side. The rails and wheels
make manipulation with containers easier.
Battery packs

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Individual Sub-System Testing
Since the fuel cell system is operating during the entire mission and represents the main power source, it
was carefully tested against endurance at its maximum power output. The system was continuously tested
by IE for more than 6 hours with no degradation of performances during the experiment. Several 6 hours
long tests were performed to prove reliability of the FC system.
A faster voltage drop could be experienced for some of the cell after some charge/discharge cycles or after
an excessive discharge below safe limits and a substitution of the less performing cells is needed for this
application
The most stressing conditions are: -
1. Very beginning of take-off phase because of maximum power in conjunction with low speed and so
poor cooling for a short time;
2. Climbing because of maximum power with strong cooling, but for a relatively long time.

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Hydrogen storage system was tested by tank manufacturer and by the supplier of the entire
system against maximum working pressure and burst pressure. Test were conducted according to
the test specification identified in ECE draft Regulation Annex 7 B9. Final proven maximum
allowable pressure is 438 bar (350 bar is the normal working pressure for this application), while the
burst pressure (representing the ultimate load of the tank) is 984 bar.
Semi-integrated System Testing
The whole fuel cell system was completely installed in the final configuration on a fuselage mock-up as
well as telemetry system; the motor/power electronic block was linked to a bench brake; hydrogen was
supplied at first from hydrogen bottles installed in a bunker for safety reasons until the system was
proven reliable and then last tests were made with the actual hydrogen system with de-rated pressure
(200 bar). Each system was provided with air blower simulating the theoretical airflow expected for that
particular system. Batteries were replaced by an external generator for most of the tests to prevent
deterioration of cells from excessive charge/discharge cycles.

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Integrated System Testing
“Power blending” ground test
This stage mainly investigated the behavior of
output power when connected to the real load
(i.e. the propeller), behavior of propeller,
handling of system partial failures,
temperatures with the real cooling system (i.e.
cooling system exposed to aircraft speed) and
finally aircraft performances in take-off and
cruise Again great attention was paid to correct
handling of the two onboard power sources
Real speed (purple line) has to be considered as a reference performance of the motor and hence the
propeller, while power input (green line) is the power requested by the throttle. It can be seen that the
system select the fuel cell (red line) as main source until 20 kW are demanded and when this threshold is
exceeded the controller starts drawing power from battery (blue line).
If for any reason the fuel cell can’t provide the requested power, the system immediately demands power from
the battery and the performance of the motor doesn’t change. Moreover the system tries to recover the fuel
cell from its inoperative state and, if successful, re-establish the fuel cell priority.

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In order to investigate system potential performances for future developing, taking-off without battery
support was checked. The aircraft was accelerated up to rotation speed (80 km/h) and, for safety reason,
the take-off was aborted before start the climbing phase. It was possible to reach the rotation speed in 480
m (380 m is the usual distance with fuel cells and battery powers), but further testing should be done for
the climbing phase in order to state that the aircraft can effectively run entirely on fuel cell power and
careful considerations about reliability have to be made to completely remove batteries from the system.
Fuel cell power vs Time

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The extensive experimental campaign carried out during ENFICA-FC project, as well as theoretical
estimations, proves that fuel cell technologies represent a promising future innovation in aeronautics as a
key-enabling technology for all-electric, zero emission, low noise aircrafts.
CONCLUSION
The hydrogen storage system, as an example, weight 52 kg and contains 1.2 kg of hydrogen. Actual
gravimetric efficiency doesn’t allow to achieve the same performances as the original aircraft both for
flight (speed, endurance)
The real strength of the “all-electric aircraft” concept doesn’t lay in an improvement of the performances,
but in the environmentally friendly use of the aircraft itself; such an aircraft could be used in airport
surrounded by urban centers, during night and in an environments that could be restricted for polluting
vehicles
Area for improvement :

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REFERENCES
1. Comprehensive investigation on hydrogen and fuel cell technology in the aviation and aerospace sectors. (2019, May
1). ScienceDirect. https://www.sciencedirect.com/science/article/abs/pii/S1364032119301157
2. ZEROe. (2021, June 24). Zero Emission - Airbus. https://www.airbus.com/en/innovation/zero-emission/hydrogen/zeroe
3. Types of hydrogen fuel - Energy Education. (n.d.). Hydrogen Fuel.
https://energyeducation.ca/encyclopedia/Types_of_hydrogen_fuel
4. Our Products / Stationary and Portable Power / Fuel Cells. (n.d.). Intelligent Energy. Retrieved March 9, 2022, from
https://www.intelligent-energy.com/our-products/stationary-power/fuel-cells/
5. Enfica. (n.d.). ENFICA-FC. Retrieved March 9, 2022, from
https://www.researchgate.net/publication/257175210_ENFICA-
FC_Design_of_transport_aircraft_powered_by_fuel_cell_flight_test_of_zero_emission_2-
seater_aircraft_powered_by_fuel_cells_fueled_by_hydrogen

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