Direct ethanol fuel cell as aircraft APU: a study for onboard waste heat recovery

  • Marcelo de Almeida Ramsdorf
  • José Alexandre Matelli
Technical Paper
  • 29 Downloads

Abstract

An advanced concept of jet aircraft (known as “more electric aircraft”) available nowadays requires electrically driven systems. In this scenario, application of low-temperature fuel cells in aircraft is an interesting alternative to generate power for the electrically driven systems with high efficiency and low environment impact. However, hydrogen fuel cells pose difficulties for aircraft designers due to safety and weight requirements related to onboard use of hydrogen. Direct ethanol polymer fuel cells (DEPFC) may overcome such difficulties, but recent publications show that DEPFC still presents low efficiency and, therefore, generates high amounts of waste heat. In this work, the use of a DEPFC as auxiliary power unit (APU) in a regional jet is proposed and opportunities for onboard waste heat recovery are evaluated. Obtained results suggest that heat recovery from DEPFC is technically feasible for cabin heating, fuel heating, and water onboard production.

Keywords

Fuel cell Ethanol Aircraft Heat recovery 

Abbreviations

APU

Auxiliary power unity

DEPFC

Direct ethanol polymeric fuel cell

GDL

Gas-diffusion layer

PEMFC

Polymer electrolyte membrane fuel cell

SOFC

Solid oxide fuel cell

Nomenclature

C

Concentration (kmol l−1)

cp

Specific heat (kJ kg−1 K−1)

\({\text{D}}_{\text{EtOH}}\)

Ethanol–water diffusion coefficient (cm2 s−1)

\({\text{D}}_{{{\text{O}}_{2} }}\)

Oxygen-water vapor diffusion coefficient (cm2 s−1)

E

Cell potential (V)

e

Specific molar exergy (kJ kmol−1)

\({\dot{{\rm E}}\text{x}}\)

Exergy rate (kW)

F

Faraday’s constant, (96,485 kC kmol−1)

G

Gibb’s free energy (kJ)

H

Enthalpy (kJ)

h

Specific molar enthalpy (kJ kmol−1)

I

Irreversibility (kW)

i

Current density (mA cm −1 )

KEtOH

Lumped parameter for ethanol oxidation (C mol−0.5cm−0.5s−1)

kc,fc

Cell effective conductivity (S cm−1)

kd

Mass transport coefficient of ethanol in the diffusion layer (cm s−1)

kf

Mass transport coefficient from feed ethanol stream to the diffusion layer (cm s−1)

Lc

Catalyst layer thickness (cm)

Ld

Gas-diffusion layer thickness (cm)

Lm

Membrane thickness (cm)

M

Molar mass of water (kg kmol−1)

\({\dot{{\rm m}}}\)

Mass flow rate (kg s−1)

N

Number of samples

\({\dot{{\rm n}}}\)

Molar flow rate (kmol s−1)

P

Pressure (atm, Pa)

\({\dot{{\rm Q}}}\)

Heat transfer rate (kW)

R

Universal gas constant (8.314 kJ kmol−1 K−1)

Rb

Contact specific resistance (Ω cm2)

s

Specific molar entropy (kJ kmol−1 K−1)

T

Temperature (K)

V

Cell voltage (V)

vd

Superficial velocity of water in the diffusion layer (cm s−1)

\({\text{W}}_{\text{el}}^{0}\)

Maximum work generated by the fuel cell (kJ)

\({\dot{{\rm W}}}_{\text{el}}\)

Cell power output (kW)

X

Molar fraction

z

Number of released electrons in fuel cell ideal reaction (kmol)

Greek symbols

\(\alpha\)

Transfer coefficient

\(\beta_{{{\text{H}}_{2} {\text{O}}}}\)

Electro-osmotic drag coefficient of water

γ

Excess air coefficient

ε

Average deviation

εd

Gas-diffusion layer void fraction

λ

Cell overpotential (V)

ρ

Specific mass (kg m−3)

σm

Membrane conductivity (Ω−1 cm−1)

ψ

Rational efficiency

Subscripts

0

Reference conditions

a

Anode

c

Cathode, concentration

fc

Fuel cell

N

Nernst

oh

Ohmic

ph

Physical

ch

Chemical

out

Output

in

Input

i

Material stream i

j

Chemical species j

Superscripts

0

Reference conditions, maximum

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Copyright information

© The Brazilian Society of Mechanical Sciences and Engineering 2018

Authors and Affiliations

  1. 1.National Civil Aviation Agency (ANAC)São José Dos CamposBrazil
  2. 2.Department of Energy, School of EngineeringSão Paulo State University (UNESP)GuaratinguetáBrazil

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