Environmental Engineering Reference
In-Depth Information
The compressor management issues discussed above are finally verified in the
range of high loads utilizing a cycle of current characterized by two successive
acceleration steps at 50 A/s, each one followed by a steady state phase, the first
one at 160 A and the second one at 240 A. A final deceleration step at 50 A/s takes
back the stack to the initial current value. The compressor management strategy
N.3 is adopted for the entire cycle length, with the aim to limit compressor con-
sumptions and check stack operation regularity in more severe conditions.
In Fig. 7.53 a, the stack current variation during the cycle and the corresponding
voltage values are reported versus time. As expected the first acceleration step
reproduces the same results shown in Fig. 7.51 in terms of stack voltage, as well as
regarding stoichiometric ratio values (Figs. 7.51 b and 7.53 b), while during the
second acceleration step a voltage decrease is observed from 52 to 45 V, with
the corresponding R diminution from 2.5 to 2 (Fig. 7.53 ). Figure 7.53 b also reports
the air flow rate profile evidencing the different values imposed by the selected
management strategy during the cycle, 33 Nm 3 /h after the first acceleration phase
and 38 Nm 3 /h during the second one.
Some acceptable individual cell irregularities during the second acceleration
phase are evidenced by the C v values shown in Fig. 7.54 , where the statistical
Fig. 7.53 a Stack voltage
and current acquisition versus
time during the dynamic
cycle characterized by two
stack current steady state
levels (160 and 240 A) and
the maximum stack current
variation of 50 A/s. Air
management strategy N.3.
b Stoichiometric ratio and air
flow rate acquisition versus
time during the dynamic
cycle characterized by two
stack current steady state
levels (160 and 240 A) and
the maximum stack current
variation of 50 A/s. Air
management strategy N.3
a
80
350
Stack Current
Voltage Current
75
300
70
250
65
200
60
150
55
100
50
50
45
40
0
0
10
20
30
40
50
60
70
80
Time [s]
b
50
5
45
4
40
35
3
30
25
2
20
15
Stoichiometric Ratio
Air Flow Rate
1
10
5
0
0
10
20
30
40
50
60
70
80
Time [s]
 
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