EVS28 KINTEX, Korea, May 3-6, 2015

Cold start studies in a PEMFC stack for

automotive fuel cells

Sungho Lee1, Sunbo Shim, Joonguen Park 1 Hyundai motor, 104 Mabuk-dong, Giheung-gu, Youngin-si, Gyeonggi-do,

446-912, Korea, Korea Corresponding Author Email :

trojan@hyundai.com*

1. Fundamentals : Structure, Principle, and Water

Introduction

2

Proton Exchange Membrane Fuel Cell (PEMFC) System

Polymer Electrolyte Membrane Fuel Cell

H2 2H+ + 2e- 2H+ + 1/2O2 + 2e-

H2OH+

H+

Load

Anode CathodePolymer

electrolyteH2 1/2O2

2e- 2e-

H2OPt/CGDLPt/C

Anode: H2(g) → 2H+ + 2e-

Cathode: 1/2O2(g) + 2H+ + 2e- → H2O(ℓ)

Overall Reaction: H2(g) + 1/2O2(g) → H2O(ℓ)

Introduction

3

in Sweden (Jan., 2012)

2. Cold start

: one of the main hurdles for a commercialization of FCEV

Measurements

1. Measuring points

4

Thermocouple

anode

cathode

coolant

GDL+MEA

7

8

9

10

1

2

3

4

5

6 11

12

13

Cross section of a real stack

Thermocouple mounting points in a bipolar plate

Flow channels, GDL, MEA and thermocouple in a cross section of fuel cell stack

5

Measurements

2. Measuring system for stack temperature: wiring, wire mapping, …

Measurements

3. Thermal behavior of fuel cell stack

: natural cooling, and convection heat transfer coefficient

1) Governing equation and solution

2) Comparing the measured T(t)

with analytic solution,

where, Ti = 60℃, T∞ = 25℃.

6

)( TThAdt

dTmc

005.0mc

hA

t

mc

hATTTT i exp)(

7

Measurements

Time(hr)

-10 ℃

-25 ℃ T∞=-10℃ T∞=-25℃

4. Soaking for cold start in a environment chamber

1) After 24 hr soaking,

Tmax = -6.6℃ @ T∞ = -10℃

Tmax = -14.4℃ @ T∞ = -25℃.

2) From the analytic solution with

measured T(t),

it needs time „t∞‟ to reach T∞ that

t∞ ≈ 34hr @ T∞ = -10℃

t∞ ≈ 57hr @ T∞ = -25℃.

5. Stack temperatures during the cold start: Ti(t)

The speed of temperature increasing: ③ > ⑤ > ④ > ⑧ >① > ②

※ the other points were lost (6, 7, 9, 10, 11, 12, 13)

8

52sec 101sec

50% rated Power Start

End of cold start

Time (sec)

7

8

9

10

1

2

3

4

5

611

12

13

Measurements

6. Temperature distribution in a bipolar plate at the end of a cold start

9

Measurements

: Sub-zero area

7

8

9

10

1

2

3

4

5

611

12

13

T∞ =-10℃

7

8

9

10

1

2

3

4

5

611

12

13

T∞ =-25℃

: Tmax

: Tmin

T∞ (℃)

Temperature(℃

)

Ti vs. T∞ at the end of the cold start

7. Temperature distribution on a bipolar plate during the cold start

: at T∞ = 10℃, Δt = 20 sec

Measurements

10

Air

Cold-start simulation

1. Governing equations

11

Ahrae Jo, Sungho Lee, Whangi Kim , Johan Ko , Hyunchul Ju a, “Large-scale cold-start

simulations for automotive fuel cells”, international journal of hydrogen energy 40 (2015)

1305 -1315

2 2

2

2 2 2 2

2

2 2

when

when

when

w

0

> &

& 0

0

sat

H O H O

H Osat sat

desub H O H O H O H O freeze

sgH Osat

sub H O H O freeze

C C

R C C C C T TS

R C C T T s

2hen & 0

H O

freezeT T s

Cold-start simulation

2. Model Geometry

12

Air in, -20℃

H2 in, -20℃

Air

GDL_anode catalyst_anode

membrane

catalyst_cathode

GDL_cathode Air

H2 H2

bipolar plate

coolant

coolant

bipolar plate

Cold-start simulation

13

Wall : Convection (T∞ = -20℃)

Symmetry condition

Air H2

GIF Animation

3. Results

: Temperature distributions on a bipolar plate during a cold start

Cold-start simulation

3. Results

: Comparing the Experiment and Simulation temperature

14

11 [℃] -20 0 -10

-5 10 [℃] 0 5

Modeling at t=110 s, T∞=-20℃

Measuring at t=52 s, T∞=-10℃

Conclusions

The temperatures on a bipolar plate of a PEMFC stack have been revealed

by measurements and large scale simulation models during a cold start.

1. Even in a overnight soaking, a stack doesn‟t reach the environment

temperature T∞ in a cold start test.

2. The maximum temperature Tmax is on the middle of a bipolar plate

during a cold start.

3. At the end of a cold start, there could be sub-zero areas according to the

cold start strategy.

It‟s needed to minimize this sub-zero region for a better cold start.

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