Case Study B: Fuel Cell Power Train for Cars - Hydrogen Fuel Cells for Road Vehicles - page 213

reported in Fig. 7.16 , showing the stack current and voltage as function of cycle
length, while R and air flow profiles are plotted in Fig. 7.17 . Only a slight voltage
decrease is measured in correspondence of the main current peaks (130 and 230 A)
compared with the steady state values. The control law of the compressor makes
possible R values only slightly lower than 1.8 for a short transient time at the end
of acceleration phases, with air flow rate up to 35 m 3 h -1 at about 230 A. In fact,
Fig. 7.18 , which shows the individual cell voltage acquisition plotted as function
of cycle length, evidences a general slight decrease of all cell voltages, with the
first one under 0.5 V already for the second peak current (130 A) and under 0.4 V
in correspondence of the highest current peak (230 A). The FCS behavior at
10 A s -1 suggests that the dynamic performance requires some modification in
management strategies for higher current rising rates. This is confirmed by the
experiment reported in Figs. 7.19 , 7.20 , 7.21 , and 7.22 , where a simple dynamic
cycle of current is tested with the same compressor management strategy of the
experiment of Fig. 7.17 . This cycle is characterized by an acceleration ramp of
50 A s -1 , a short stationary phase at 220 A and a deceleration step at the same rate
of acceleration. In Fig. 7.19 , the acquisition data for the current cycle is reported

Fig. 7.17 Stoichiometric
ratio and air flow rate versus
time for the experiment of
Fig. 7.16

100 5

90

4

80

70

3

60

50

2

40

Air Flow Rate

30

1

Stoichiometric Ratio

20

10 0

700 750 800 850 900

Time [s]

Fig. 7.18 Individual cell
voltage acquisition versus
cycle length during the
experiment of Fig. 7.16

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

650 700 750 800 850 900

Time [s]