Environmental Engineering Reference
In-Depth Information
0.8
0.6
0.4
0.2
0
1
4
7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79
Cell Number
Fig. 7.26 Individual cell voltage acquisition during the experiment of Fig.
7.23
at the instant of
maximum acceleration (t = 175 s, 230 A)
Fig. 7.27 Stack power ver-
sus time during a sequence of
eight fast load variations from
0.7 to 8.5 kW
10
8
6
4
2
0
0
150
300
450
600
750
900
time [s]
phases. No cell drops under 0.4 V, except for the first one whose voltage decreased
at about 0.3 V, confirming the same trend already observed at 10 A s
-1
[
5
].
The results of the FCS characterization performed with faster load variations,
composed by a sequence of eight fast load variations from 0.7 to 8.5 kW, are
reported in Figs.
7.27
,
7.28
,
7.29
,
7.30
, and
7.31
. In Fig.
7.27
, the stack power
versus test length, with an acceleration slope of about 6 kW/s, is shown. The value
of about 47C is selected as initial stack temperature to overcome the limitations
due to the electrochemical reaction and diffusion kinetics with respect to warm-up
conditions. The inlet air is humidified at the same temperature, while the cooling
system is controlled to maintain the stack temperature in the range 50-55C. The
hydrogen purge and air feeding strategies are evidenced by the acquisitions of
hydrogen pressure and stoichiometric ratio during the test length (Figs.
7.28
and
7.29
,
respectively).
Hydrogen
pressure
drops
every
45 s
according
to
the
