MEMORANDUM

TO: Supervisor for New Technology Development Department

FROM: Technology Development Engineering Leader

DATE: 1 July, 2015

SUBJECT: Review on Fuel Cell Technology for Its Potential to Develop More Fuel

Efficient Regional Jets

Here is the report you requested on June 18 as to research on fuel cell technology for its

potential to develop more fuel efficient regional jets.

Based on this research, it was validated that fuel cell technology brings to our regional jets a

lot of benefits in terms of achieving further fuel efficiency. As Airbus suggested, integrating

fuel cell technology into our regional jets systems could lead to as much as 15 percent more

fuel efficiency.

In this paper, fuel cell technology is studied based on 3 essential aspects of mechanism, fuel

efficiency, and applicability to passenger aircrafts. For the mechanism of fuel cell technology,

its fundamentals are revealed. Next, fuel efficiency of fuel cell technology is validated.

Finally, the potential applicability of fuel cell technology to passenger aircrafts is examined.

I am grateful to my supervisor, Cheryl Rauh for helping me solve my questions to compose

this research paper in a professional way. Her support contributed greatly to the success of

completing this research project.

Please email me if you perceive any questions in regards to the contents of this research

paper. I would be happy to answer your questions and also to implement additional research

at your request.

Review on Fuel Cell Technology

for Its Potential to Develop More Fuel Efficient Regional Jets

Prepared for: Cheryl Rauh, Supervisor for New Technology Development Department

Prepared by: Yuki Busujima, Technology Development Engineering Leader

ii

Abstract

Skylead is facing a competitive age to maintain share of its regional jets (RJs) due to other RJ

manufacturers’ technological advances in fuel efficiency and emergence of new RJ producers.

In order to maintain share of our RJs, Sky lead must develop further fuel efficient RJs with

new technologies.

However, before development, Skylead must build solid foundation of what technology

presents a viable option to achieve our goal. In this paper, fuel cell technology is examined to

validate its potential for achieving further fuel efficiency as Airbus suggested this technology

could contribute to as much as 15 percent more fuel efficiency. I conducted research based on

3 essential aspects of fuel cell technology: mechanism, fuel efficiency, and applicability to

passenger aircrafts using ProQuest Research Libraries and Scholar.Google.com. Also, I only

utilized credible sources based on 5 aspects: currency, relevance, authority, accuracy, and

purpose to compose this paper. Below are the findings on 3 essential aspects of fuel cell

technology.

First, as to the mechanism of fuel cell technology, it was revealed that fuel cell requires other

subsystems to compose a fuel cell system and the fuel cell system then becomes a part of

powerplant that can be applied to passenger aircrafts.

Second, as to the fuel efficiency of fuel cell technology, it was validated that fuel cell

powered powerplants are more fuel efficient than the conventional internal combustion

powerplants.

Finally, as to the applicability of fuel cell technology to passenger aircrafts, it was found that

fuel cell technology is applicable to passenger aircrafts with some tasks that have to be solved

and the application of fuel cell system to passenger aircrafts does achieve further fuel

efficiency with additional benefits compared to the currently used systems.

Through this research, I conclude that the fuel cell technology is worth for Skylead to invest

our funds in to develop further fuel efficient RJs. Based on my conclusion, I recommend the

next research as to making partnerships with other organizations in order to integrate their

fuel cell technologies into our regional jet systems, which will also enable us to estimate

necessary costs for our new development.

Table of Contents

Introduction ............................................................................................................ 1

Background ......................................................................................................... 1, 2

Research Methods .................................................................................................. 2

Research Results ................................................................................................... 2

1. Mechanism of Fuel Cell Technology ........................................................................ 2, 3

2. Fuel Efficiency of Fuel Cell Technology ................................................................ 4, 5, 6

3. Applicability of Fuel Cell Technology to Passenger Aircrafts ..................... 7, 8, 9, 10, 11

Conclusion ............................................................................................................. 11

References ....................................................................................................... 12, 13

List of Illustrations

Figure 1. Illustration of Proton Exchange Membrane Fuel Cell .................................. 3

Figure 2. Decomposition of fuel cell aircraft modeling into

application, powerplant system and subsystem modeling domains ................... 3

Figure 3. Results of powerplant [fuel efficiency] comparison ......................................... 6

Figure 4. Multifunctional architecture of the fuel cell system ............................................. 9

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Introduction

Skylead is facing a competitive age of regional jet (RJ) manufacturing industry due to other

RJ manufacturers’ technological advances for fuel efficiency and emergence of new RJ

manufacturers. In order to maintain demand of our RJs in the near future, we must build solid

foundation of what technology presents a viable option for us to develop further fuel efficient

RJs. In this paper, fuel cell technology is studied through research utilizing credible data

bases and credible sources based on its 3 essential aspects of mechanism, fuel efficiency, and

applicability to passenger aircrafts so as to examine whether this technology has a potential to

develop further fuel efficient RJs.

Background

Skylead has been expanding share of its regional jets (RJs) among regional airlines mainly in

the US since 1990s. It is estimated that 41 percent of the US passenger aircraft fleet is

operated by regional carriers and RJ deliveries were dominated by the US market (Curtis,

Rhoades, & Waguespack Jr, 2013). We have led RJ manufacturer industry with pioneering

technologies for fuel efficiency. Many regional airlines have chosen to fly our RJs due to our

top-notch fuel efficient technologies.

However, our competitors of Bombardier and Embraer have come to develop fuel efficient

RJs to a level close to ours. In the next 18 years, it is forecast that these two manufacturers

will grow significantly in sales by meeting higher demand and replacing existing older

aircrafts (Curtis et al., 2013). At the same time, new companies are entering this industry,

such as Mitsubishi Aircraft Corporation owned by Mitsubishi Heavy Industries from Japan,

COMAC from China, Sukhoi company from Russia, and HAL/NAL Regional Transport

Aircraft as a future entrant from India.

On the other hand, due to the rise of fuel costs, it is forecast that “the needs [of airlines in the

world] to replace older and less efficient airplanes” will occupy as much as 40 percent of the

new orders of airplanes. In addition, with the definition of RJ expanding to the aircraft that

can carry up to 130 passengers, it is predicted that RJs will occupy “70 percent of the total

world fleet” by 2030 (Curtis et al., 2013).

With this trend, regardless of other competitors, there exist chances for us to succeed in

maintaining future demand of our RJs by developing further fuel efficient RJs with new

technologies. As an option, fuel cell technology is examined in this paper as this technology

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could contribute to as much as 15 percent more fuel efficiency by integrating to aircrafts’

non-propulsion systems (Graham-Rowe, 2012).

Research Method

To examine whether fuel cell technology has a potential to develop further fuel efficient RJs,

I conducted research based on 3 essential aspects of fuel cell technology: mechanism, fuel

efficiency, and applicability to passenger aircrafts using ProQuest Research Library and

Scholar.Google.com with keywords such as fuel cell Fundamentals, fuel cell efficiency, and

applications of fuel cells to aircrafts.

After gathering research sources, I analyzed each of them based on 5 aspects: currency,

relevance, authority, accuracy, and purpose in order to utilize only credible sources for this

research paper.

Finally, to explain 3 essential aspects of fuel cell technology, I referenced at least 3 sources

for each aspect.

Research Results

1. Mechanism of Fuel Cell System

In this section, I explain how fuel cell system works. “A fuel cell consists of two electrodes- a

[positive electrode] (or anode) and a [negative] electrode (or cathode)- sandwiched around an

electrolyte” and it functions as a device in which reactants’ chemical energy is directly

transformed into electrical energy and harmless products: water and heat (U.S. Department of

Energy; Bradley, 2008). Fuel cell requires hydrogen and oxygen or another oxidizing agent to

produce the dc(direct current) voltage. An illustration of one of the fuel cells, Proton

Exchange Membrane fuel cell (PEMFC), is shown in Figure 1 (U.S. DOE, 2015).

As for the difference between conventional batteries and fuel cells, they are similar in that

both of them derive electrical power “from a chemical reaction.” However, battery runs down

when it exhausts stored reactants; fuel cells continue the production of electricity “as long as

its external fuel supply lasts” (Klesius, 2009).

In order to utilize fuel cell as a source of electric power, a number of fuel cells are integrated

to compose one battery, often called fuel cell stack. Then, this fuel cell stack is only a

component of fuel cell system; several subsystems such as water management, thermal

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management, hydrogen storage, hydrogen management, controls, etc compose fuel cell

system as a whole. Each of them are separate physical components and compose the fuel cell

system as shown in Figure 2 (Bradley, 2008). In addition, other power conditioners, generally

consisting of “a power management device, a traction electric motor, and a motor controller,”

convert the fuel cell system output into the required output voltage and electrical current

(Emadi, Rajashekara, Williamson, & Lukic, 2005; Bradley, 2008). This powerplant then can

be applied to aircrafts. As you can see, fuel cell system works as a part of a lot of other

systems.

Figure 1. Illustration of Proton Exchange Membrane Fuel Cell (PEMFC) (Taken from

U.S. DOE, 2015)

Figure 2. Decomposition of fuel cell aircraft modeling into application, powerplant

system and subsystem modeling domains (Adapted from Bradley, 2008)

Application

Wing

Mission

Fuselage

Powerplant

Energy Mgt.

Electric Motor

Propeller

Fuel Cell System

Radiator Compressor H2 Tank

Controls Power Mgt.

Stack

Humid. MEA

“A fuel, such as hydrogen, is fed to

the anode, and air is fed to the

cathode. In a hydrogen fuel cell, a

catalyst at the anode separates

hydrogen molecules into protons

and electrons, which take different

paths to the cathode. The electrons

go through an external circuit,

creating a flow of electricity. The

protons migrate through the

electrolyte to the cathode, where

they unite with oxygen and the

electrons to produce water and

heat” (U.S. DOE, 2015).

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2. Fuel Efficiency of Fuel Cell Technology

In this section, I explain how fuel cell technology is more feul efficient than conventional

power-generation technology. According to Emadi and others, fuel cell technology performs

overall fuel efficiency and quieter operation due to few moving parts (2005). However, there

exist several types of fuel cell technologies that have different strengths and weaknesses to

achieve fuel efficiency. “[F]or transportation applications” in the near future, “[P]roton

exchange membrane fuel cell (PEMFC), the solid oxide fuel cell (SOFC), the alkaline fuel

cell, and the phosphoric acid fuel cells” are considered primary fuel cells (Bradley, 2008).

In order to compare the “energy density [or fuel efficiency] of fuel cell and conventional

powerplants at the variety of power and energy scales suitable for wide aviation

applications,” Bradley conducted a study. The study made “a conceptual comparison” on

energy production rate or fuel efficiency for various powerplants with respect to different

power requirements and endurance. 5 types of powerplants were utilized for the conceptual

comparison as follows (Bradley, 2008).

1. Internal Combustion (IC) engine fueled by gasoline

2. PEM fuel cell with gaseous hydrogen storage

3. PEM fuel cell with liquid hydrogen storage

4. SOFC fueled by propane

5. PEM fuel cell fueled by neat methanol

Settings of the Bradley’ s Study

“[5 types of powerplants] are composed of fuel storage and energy conversion

components, which convert the energy stored as fuel to propulsive energy.”

“The specific energy [or fuel efficiency] of the powerplant is the rotational

mechanical energy output of the powerplant, [Watt-hours (Wh)], divided by the

sum of the fuel, fuel tank, and energy converter (engine or fuel cell) mass, [kg].”

In another word, the specific energy or fuel efficiency measure in this study is

Wh/kg.

“The specific energy of the powerplant is calculated at endurances between 1

and 100,000 min. and powers between 10 and 100,000 W.”

(Bradley, 2008)

The resultant graphs are shown in Figure 3 (Bradley, 2008).

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Analyses of the Conceptual Comparison Results.

A) Under the lowest power requirement of 10 watt for the multi-hour endurance of

1,000 minutes, PEM fuel cell fueled by neat methanol outperformed other

powerplants in fuel efficiency (red dotted line showing 1000-2000 Wh/kg) and

proved its aptitude for “the low-power, high energy, small scale applications.”

B) Under the low power requirement of 100 watt for the long endurance of more

than 10,000 minutes, all of the fuel cell powerplants “exhibit higher [fuel

efficiency] than the IC powerplant.”

C) Under the middle power requirement of 1,000 watt for the long endurance of

more than 10,000 minutes, SOFC and IC powerplants perform better fuel

efficiency than the other powerplants except for hydrogen PEM fuel cell.

D) Under the highest power requirement of 100,000 watt for the long endurance of

100,000 minutes, even though the IC engine exhibit higher fuel efficiency than

PEM fuel cell with gaseous hydrogen storage and PEM fuel cell fueled by neat

methanol, PEM fuel cell with liquid hydrogen storage performed much higher in

fuel efficiency than the other powerplants.

(Bradley, 2008)

Overall, except for the condition A, liquid hydrogen PEM fuel cell outperformed other

powerplants. Bradley concludes that each fuel cell has different strengths and weaknesses to

achieve fuel efficiency and strength of each depends on where these fuel cells supply power

and how long they get used (2008).

This study validates the overall better fuel efficiency of fuel cell powerplants than the

conventional powerplants and its usefulness for aircraft applications.

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Figure 3. Results of powerplant [fuel efficiency] comparison (Adapted from Bradley, 2008)

A

B

C

D

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3. Applicability of Fuel Cell Technology to Passenger Aircrafts

Fuel cell technology has not yet been realized in passenger aircrafts. However, several

experiments were successfully conducted by aeronautical institutes and large transportation

jet manufactures of Boeing and Airbus toward its applications to passenger aircrafts. In this

section, I introduce potential candidates of fuel cell technologies, successful experimental

examples with fuel cells integrated to aircrafts, potential parts of passenger aircrafts, and

general tasks for the realization of fuel cell applications to passenger aircrafts.

Potential Candidates of Fuel Cell Technologies

For fuel cell applications to passenger aircrafts, two fuel cell technologies of the SOFC and

PEMFC are primary candidates. However, there still exist tasks for their applications.

Solid Oxide Fuel Cell (SOFC) : SOFC is considered “theoretically and

conceptually well-suited [for passenger aircraft applications] because of

[its] similarity in operating temperature and the possible hybrid

configurations with gas turbine to increase [fuel] efficiency.” However,

SOFC has mainly two tasks: very low power density and necessity of

incorporating “compact and reliable fuel processors” for aircraft

applications (Renaouard-Vallet et al., 2010).

Proton Exchange Membrane Fuel Cell (PEMFC) : As PEMFC was successfully

integrated into automobiles for commercialization, PEMFC is also

considered good candidate for the near-term passenger aircrafts’

applications. However, PEMFC also has several tasks: necessities of

“improving the specific power of the stack,” “[reductions] of the weight of

the [related] components,” and investigations of flight-operation behaviors

(Renaouard-Vallet et al., 2010).

Successful Experimental Examples of Fuel Cell Applications

Boeing attempts : Boeing has successfully developed and flew a two-seater

glider powered by the combination of PEMFC and a lithium-ion battery.

Based on this success, “Boeing studies fuel cells” in order to reduce the

burden of airliner engines from running generators for partial onboard

electricity. Boeing claims that there exist tasks on dependability of fuel

cells in extreme flying conditions (Klesius, 2009).

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Airbus attempts: Airbus has successfully integrated a “20 kW emergency power

[PEMFC] system” into A320 and the fuel cell system has successfully

operated the A320’s control surfaces in various flight conditions. Airbus

claims the needs “to increase [Fuel Cell] power density” (Renaouard-Vallet

et al., 2010; Klesius, 2010).

Potential Parts of Passenger Aircrafts for Fuel Cell Technology Applications

Auxiliary Power Unit (APU)

The biggest experimental trend on fuel cell application to the passenger aircraft

is to replace the auxiliary power unit (APU) with fuel cell technology. On the

ground, aircraft systems rely on supplies of electric energy, compressed air and

hydraulic pressure from the APU for their operations before main engines start.

Those aircraft systems include “avionics systems, air conditioning, and the de-

icing devices.” Moreover, the APU is the kick-starter for the main engines. The

APU hands all of its jobs previously mentioned to the main engines thereafter.

Replacing the APU with fuel cell technology for the electrical ground supply

can be great benefits because the APU has many negative aspects such as a low

fuel efficiency of less than 20% of its use, greenhouse gas emission of nitric

oxide and carbon monoxide, and the noise emissions. Replacing the APU with

fuel cell systems can solve all of these negative aspects.(Renouard-Vallet,

Saballus, Schmithals, Schirmer, Kallo, & Friedrich, 2010).

Ram Air Turbine (RAT)

Another potential application is to the Ram Air Turbine (RAT), which produces

electric energy from the ram air to the propeller of its system in the case of all

engine failures. When all engines fail, the aircrafts’ control surfaces are no

longer controllable without other means of electricity supply; the RAT is the

alternate source of electricity supply in this situation. The fuel cell system

supplies power better than the RAT, so that it gives pilots greater controllability

of aircrafts. Since the RAT is also the causes of high maintenance costs and

worse aerodynamics when it is active, replacing this system with fuel cell

technology can lead to overall efficiency (Renaouard-Vallet et al., 2010;

Lucken, Brombach, & Schulz, 2010).

Reducing the Load of Water at Takeoffs

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Fuel cell system can produce about “0.5-0.6 L of water per kW h electrical

power”; in other words, fuel cell system can produce about “50 L of water” with

“100 kW fuel cell power (appropriate for a large aircraft)” for one hour of

operation. In passenger aircrafts, toilets and air humidifier in a cabin can utilize

this substantial amount of water. This utilization of fuel cell generated water

results in the reduction of the load of water at takeoffs; some carriers load as

much as 3000 pounds of water at takeoffs, which is the substantial portion of the

takeoff weight. In order to improve and optimize this potential use of water

generated by fuel cell systems, the system for the distribution of the water inside

a cabin and the water quality are “still [under] research and development”

(Renaouard-Vallet et al., 2010; Graham-Rowe, 2012).

Reuse of the Fuel Cell Exhaust Air for Inerting Systems of the Fuel Tanks

Fuel cell exhaust air contains very little oxygen, as little as 10% of the exhaust

air, so that the fuel cell exhaust air can be utilized for “fire retardation,

suppression, or explosion prevention” inside the fuel tanks; jet fuel cannot start

burning with the “oxygen contents below 12 % by volume.” Therefore, nitrogen

based inerting system can be removed from the fuel tanks by utilizing the fuel

cell exhaust air (Renaouard-Vallet et al., 2010).

Other potential applications of fuel cell technology include power source of avionics,

electrical motor-powered ground taxing, exhaust heat utilization for anti-icing device

of aircrafts. General illustration of application points on passenger aircrafts are

shown in Figure 4 (Renaouard-Vallet et al., 2010).

Figure 4. Multifunctional architecture of the fuel cell system (Taken from

Renaouard-Vallet et al., 2010)

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General Tasks for the Realization of Fuel Cell Applications

Prevention of Short Circuits within the Fuel Cell System

In order to realize the replacement of the APU with a fuel cell system, the

development of “new protection arrangements” for a new grid architectures

optimized for fuel cell systems and modern aircrafts is a must. Typically, “fuel

cell systems [require] special operational conditions” and the biggest task of the

application of fuel cell as electricity supply is to prevent the onset of short

circuits within the fuel cell system as it reduces the durability of the fuel cell and

destructs fuel cell stacks due to overheating (Lucken, Brombach, & Schulz.,

2010).

Prevention of Fuel Cells’ Material Degradation

Fuel cells “[are] prone to material degradation” under various operating

conditions of “low reactant flows,” “high and low humidification levels,” and

“high and low temperatures” With these conditions, the 2-10 μV/ h is the general

degradation range of fuel cells. The management of these conditions “within

application and system abilities” is a key to a success for different applications

of fuel cells. To meet the requirements of different applications, fuel cells may

also be suited to “be custom designed” (Knights, Colbow, St-Pierre, &

Wilkinson., 2004). So, if we adapt fuel cell technology for our new

development, we also have to develop operating condition management system

so as to prevent fuel cell degradation.

Monitoring and Detection of Abnormalities in the Mechanical Behavior of

Fuel Cell Stack under Vibrating Conditions

Accurate understanding of fuel cells’ mechanical behavior and “the effects of

mechanical loads on their structures [in vibrating environment]” is a must in

order to integrate fuel cells into transportation systems and particularly into

aircrafts. For this purpose, three-dimensional model enabling the prediction of

fuel cell mechanical behavior “in the three axes of excitations: X, Y and Z,”

which is developed based on Artificial Neural Network (ANN) approach, was

proposed by Rouss, Candusso, and Charon. The ANN global model is very

useful to reduce computation time “instead of creating a model for each axis.

This proposed model can be utilized to monitor and detect “abnormalities in the

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mechanical behavior of [fuel cell] stacks placed under vibrating conditions”

(Rouss, Candusso, & Charon., 2008).

Conclusion

Skylead is facing a competitive age to maintain share of its regional jets (RJs) due to other RJ

manufacturers’ technological advances in fuel efficiency and emergence of new RJ producers.

To continue to maintain share of our RJs in the world, Skylead must start to develop further

fuel efficient aircrafts with new technologies. Fuel cell technology is the potential to achieve

this goal, as this technology could contribute to as much as 15 percent more fuel efficiency

by integrating to aircrafts’ non-propulsion systems (Graham-Rowe, 2012).

In this paper, fuel cell technology was studied based on 3 essential aspects; mechanism, fuel

efficiency, and applicability to passenger aircrafts in order to examine its potential for our

new development. For the mechanism of fuel cell technology, the system of fuel cell and the

architecture of fuel cell system were described. In this section, it was found that the fuel cell

system is composed of other power conditioners and it becomes a part of powerplant for it to

be applied to passenger aircrafts.

As for the fuel efficiency of the fuel cell technology, 4 types of fuel cell powerplants were

compared with the conventional internal combustion powerplant in order to validate the fuel

efficiency of fuel cell technology. In this section, it was found that overall fuel cell

powerplants are more fuel efficient than conventional powerplants and the different fuel cell

technology has different strengths based on the purposes of utilization.

Finally, potential candidates of fuel cell technologies, successful experimental examples,

potential parts of passenger aircrafts, and general tasks were examined for the applications of

fuel cell technology to passenger aircrafts. In this section, it was found that applications of

fuel cell systems to passenger aircrafts are possible with some tasks and have a number of

benefits in terms of achieving more fuel efficiency compared to the currently used systems.

Through this research on the potential of the fuel cell technology to develop further fuel

efficient RJs, it was validated that the fuel cell technology is worth for Skylead to invest our

funds in to achieve our goal. Based on this validation, I recommend the next research on the

institutes and companies that have developed fuel cell technologies and Skylead will be able

to make partnership with in order to develop fuel cell systems that can be integrated into our

regional jet systems. With this next research, we will also be able to estimate costs to develop

our next generation RJs.

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References

Bradley, T. H. (2008). Modeling, design and energy management of fuel cell systems

for aircraft (Order No. 3345942). Available from ProQuest Dissertations &

Theses Global. (304653903). Retrieved from

http://search.proquest.com.er.lib.k-state.edu/docview/304653903?accountid=11789

Curtis, T. Rhoades, D. & Waguespach Jr, B. P. (2013). Regional Jet Aircraft Competitiveness:

Challenges and Opportunities. Embry-Riddle Aeronautical University ERAU Scholarly

Commons. Retrieved from

http://commons.erau.edu/cgi/viewcontent.cgi?article=1015&context=db-management

Emadi, A., Rajashekara, K., Williamson, S.S., Lukic, S.M. (2005, May).

Topological overview of hybrid electric and fuel cell vehicular power

system architectures and configurations. Vehicular Technology, IEEE Transactions

on, vol.54, no.3, pp.763-770. doi: 10.1109/TVT.2005.847445

Graham-Rowe, D. (2012, August). Fuel Cells Take to the Runway, Airbus will test a system

that could reduce fuel consumption by 15 percent. MIT Technology Review. Retrieved

from http://www.technologyreview.com/news/428693/fuel-cells-take-to-the-runway/

Klesius, M. (2009, February). How Things Work: Flying Fuel Cells - Out of gas? Not a

problem. AirspaceMag.com. Retrieved from http://www.airspacemag.com/flight-

today/how-things-work-flying-fuel-cells-47181830/?no-ist=&page=2

Knights, S. D., Colbow, K. M, St-Pierre, J., & Wilkinson, D. P. (2004, March 10). Aging

mechanisms and lifetime of PEFC and DMFC. Journal of Power Sources, vol. 127,

1-2, pp. 127-134, ISSN 0378-7753. Retrieved from

http://www.sciencedirect.com/science/article/pii/S0378775303009467#

Lucken, A., Brombach, J., & Schulz, D. (2010, October). Design and protection of a high

voltage DC onboard grid with integrated fuel cell system on more electric aircraft.

Electrical Systems for Aircraft, Railway and Ship Propulsion (ESARS), vol., no.,

pp.1, 6, 19-21. doi: 10.1109/ESARS.2010.5665245

Renouard-Vallet, G., Saballus, M., Schmithals, G., Schirmer, J., Kallo, J.,

& Friedrich, A. (2010). Improving the environmental impact of civil aircraft by

fuel cell technology: concepts and technological progress. Royal Society of Chemistry,

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1458-1468. doi: 10.1039/B925930A

Rouss, V., Candusso, D., Charon, W. (2008, November). Mechanical behaviour of a fuel cell

stack under vibrating conditions linked to aircraft applications part II:

Three-dimensional modelling. International Journal of Hydrogen Energy, vol33, 21,

pp. 6281-6288, ISSN 0360-3199. Retrieved from

http://www.sciencedirect.com/science/article/pii/S0360319908009889

U.S. Department of Energy. (2015). FUEL CELLS. Washington, DC: Office of Energ

Efficiency & Renewable Energy. Retrieved from http://energy.gov/eere/fuelcells/fuel-

cel