IEEE Electrification Magazine - December 2017 - 73

Fuel Cells and Aircraft
In the context of the More Electric Aircraft (Weimer
1993), one of the concepts supported by the European
More Open Electrical Technologies project, the electrical
power requirements of an aircraft are set to increase
(Roboam et al. 2012) thanks to recent advances in power
electronics (Rosero et al. 2007). An aircraft may be subject to various failures, in particular to the total loss of
the engines or electrical power. These failures must
remain acceptable (Mehdi and Woods 1989). For most
large aircraft, a backup system composed of a RAT is
used to generate emergency power (Bolognesi 2009). As
new and future flight control actuators are electrical
(Van Den Bossche 2003), the load profile supplied by this
backup system is very intermittent (Figure 1). As the
increase in electrical power demand is becoming very
restrictive for the aircraft structure, which must include
an increasingly large RAT, researchers have been looking at replacing this turbine with a fuel cell (GarciaArregui 2007). In addition, a fuel cell system has other
advantages compared to the current RAT system's properties (Wörner 2009): it operates independently of the
aircraft's speed and altitude; it can be stopped at any
time if the main engines are recovered, while the RAT
cannot be retracted once it has been extended; and it
may reduce maintenance. Motapon et al. have also
recently conducted and presented research in Canada
with experimental tests on replacing the RAT with a
hybrid fuel cell.
The fuel cell indirectly [via reduction-oxidation reaction (redox)] makes H2 react with O2 ( Pera et al. 2013).
There are several possible strategies for supplying the
gases (Garcia-Arregui 2007). H2 may be produced on
board by reforming kerosene (Lenz and Aicher 2005,
Ibarreta and Sung 2006), or embedded in a compressed
form. O2 may be taken from the ambient air using a
compressor or carried in a compressed form. All scenarios were examined and assessed by Garcia-Arregui, and
the most relevant solution for the emergency power
application would be carrying both gases in a compressed form, which would eliminate the complex stage
of reforming the kerosene and ensuring the quantity
and/or quality of the air in the event of an emergency.
This H2/O2 solution is studied and experimentally validated in this article.
Research on fuel cell applications in aviation goes
beyond the mere use in emergency power units (Curtin
2010). A fuel cell could replace the gas turbine that currently performs the auxiliary power unit (APU) function,
which essentially supplies the aircraft with power when

it is on the ground. This would reduce aircraft noise and
gas emissions on the ground. A hybrid fuel cell/battery
system has been proposed to perform this function (Eid
et al. 2010). Looking even further into the future, the
hybridization of a high-temperature fuel cell and a turbine for this APU has been studied (Rajashekara et al.
2008). In the Elektrische Basissysteme in einem CFK
Rumpf: Architektur und Auslegung project (2007-2009,
funded by the Federal Ministry of Economics and Technology/Airbus, EYI-058/07) in Germany, researchers are
studying various applications based on fuel cells (Wörner
2009): the emergency power unit, multifunctional fuel cell
system (power, water, and inerting), and green taxiing on
the ground. Incorporating fuel cells in aviation would
seem to require multifunctional technology to compete
with the other current highly integrated technologies.
Given the intermittent character of the emergency
profile to be achieved as displayed in Figure 1, it is useful
to associate a source with high specific power with the
main power source to avoid oversizing (Turpin et al.
2012). Therefore, the current RAT has already been the
subject of optimization studies (to reduce its size and
weight) by associating it with ultracapacitors (Roboam
et al. 2011, Rafal et al. 2010) based on the duration of the
intermittent loads to be satisfied (high power peaks but
with relatively low energy). For a fuel cell emergency
power unit, there is also the issue of not oversizing the
fuel cell ( Jiang and Dougal 2006). However, there are
other reasons to justify this hybridization, such as in
Martínez et al., or Bizon et al. for vehicles, e.g., for H2/air
operation, it can also be used to compensate for the dynamics of the air compression (Zhan et al. 2008).
The work in this article is in line with previous theoretical work conducted in the context of the European
CELINA-Fuel Cell Application in a New Configured Aircraft-project. Several electrical architectures have been

Peak Value = 70 kW

70
60
50
Power (kW)

An experimental validation (at a reduced ratio scale of
1:10) allows for an analysis of the proposed principles. The
experiment is conducted in two stages. In the initial validation, a fuel cell physical emulator is used as the main
source, before introducing an actual fuel cell.

40
30
20

Mean Value = 40 kW

10
0

100

150 200 250
Time (s)

300

350

Figure 1. A typical load profile for the sizing of an emergency power
system (approach phase).

IEEE Elec trific ation Magazine / D EC EM BE R 2 0 1 7

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