Environmental Engineering Reference
In-Depth Information
Fig. 7.32 Stack voltage,
current, and temperature ver-
sus time during warm-up test
at 150 W/s
200
Stack Voltage [V]
Stack Current [A]
Stack Temperature [°C]
150
100
50
0
0
100
200
300
400
500
600
Time [s]
Fig. 7.33 Stoichiometric
ratio and stack power versus
time during the acceleration
phase in warm-up test at
150 W/s
8
Stoich. Ratio
Stack Power [kW]
6
4
2
0
5
15
25
35
45
55
65
Time [s]
140 A at the of the acceleration phase, then slowly decreases to 130 A as the
system is controlled to maintain the constant power of 7.8 kW. The stoichiometric
ratio profile (Fig.
7.23
) evidences a regular variation passing from the highest
value at low load (R = 6.7) to the final value of R = 1.9 at the power level of 7.8
kW. The data shown in Figs.
7.32
,
7.33
suggest that the operative conditions
selected for this tests satisfy a acceptable dynamic behavior of the FCS, as the total
stack voltage results comparable to that obtained in steady state conditions. This is
confirmed by the analysis of the individual cell voltages acquired during the whole
experiment, whose results are reported in Figs.
7.34
,
7.35
, where C
v
versus time
and individual cell voltages at the moment corresponding to the maximum C
v
are
shown, respectively. In particular, C
v
resulted always lower than 1.2% and almost
constant during the test (Fig.
7.34
), evidencing a uniform distribution of cell
voltages (Fig.
7.35
), with the minimum voltage (0.63 V) for the cell N.1 at the end
of the acceleration phase (maximum C
v
) and most cell voltages comprised
between 0.65 and 0.67 V.
The warm-up phase is also studied using a slope of acceleration 10 times
higher (1,500 W/s). The results are shown in Figs.
7.36
,
7.37
,
7.38
, and
7.39
evidencing the tendency of the FCS to operate with irregularity only at the end of
acceleration phase, in particular the total stack voltage decreases to about 50 V for
