Environmental Engineering Reference
In-Depth Information
Fig. 6.22 Stack voltage,
current, and temperature pro-
files versus time during a R40
cycle and b R47 cycle
Figure
6.22
a shows that during the R40 cycle the stack current profile versus time
reproduces the cycle peaks reported in Fig.
6.21
b, with accelerations always
B100 W/s, while voltage varies accordingly and temperature does not appreciably
increase (about 0.25 K/min). Instead, during R47 cycle (Fig.
6.22
b) the maximum
power value reached by the FCS is limited to about 1 kW (about 48 A in Fig.
6.22
b),
while the temperature increases at 0.5 K/min from 315 to 323 K (a value reached
after the fourth cycle), because of the higher power involved and longer test duration
with respect to the experiment of Fig.
6.22
a.
In Fig.
6.23
a, b, the coefficient of variation is reported as function of time for
R40 and R47 driving cycles, respectively. Fast and transient excursions outside the
optimal region of Fig.
6.20
occur at fuel cell system minimum power of both
cycles and for the highest power peak of R40 (170 s in Fig.
6.22
a). However, for
R40 cycle these excursions do not involve significant losses of cell voltage
uniformity, as evidenced by values of coefficient of variation always below 2%
(Fig.
6.23
a), indicating that the short durations of shifts from the optimal region of
