Environmental Engineering Reference
In-Depth Information
Fig. 7.49 C
v
profiles versus
cycle length for the experi-
ments of Figs.
7.47
and
7.48
4
3,5
Qair=33 Nm3/h
Qair=24 Nm3/h
3
2,5
2
1,5
1
0
10
20
30
40
50
60
Time, s
Fig. 7.50 a Stack voltage
and current acquisition versus
time during the dynamic
cycle characterized by the
maximum stack current vari-
ation of 25 A/s. Air manage-
ment strategy N.3.
b Stoichiometric ratio and air
flow rate acquisition versus
time for the experiment (a)
a
80
250
75
Stack Current
200
Stack Voltage
70
150
65
60
100
55
50
50
45
0
0
10
20
30
40
50
60
Time [s]
b
40
5
35
4
30
25
3
20
2
15
10
1
Stoichiometric Ratio
5
Air Flow Rate
0
0
10
20
30
40
50
60
Time [s]
durability requires stoichiometric ratio values higher than those optimized for
stationary operations or for very slow dynamics.
In order to identify the best compromise between compressor consumption and
stack dynamic performance the management strategy N.3 is verified for two different
current variation rates, 25 and 50 A/s (Figs.
7.50
and
7.51
, respectively). This
management strategy allows R values higher with respect to the strategy N.4 to be
realized, in particular reaching R = 2.5 (33 Nm
3
/h) at 160 A. For both dynamic
