Environmental Engineering Reference
In-Depth Information
The results obtained from this investigation can be utilized to design the power
train control strategies on the same R40 driving cycle.
7.3.1 Performance of the FCS During Load Variations
For the following tests, the fuel utilization coefficient is set at the constant value of
0.90, the stoichiometric ratio ranges between 6 and 1.8, for a stack power from
700 W to 12 kW. With regard to the stack humidification, the inlet air is saturated
at room temperature (290-300 K) to minimize the amount of energy required for
the best membrane hydration and reduce the electric consumption of the humid-
ifier and the purge frequency [
4
]. As a consequence, the stack temperature is
controlled at about 315 K, to avoid any dehydration of the membranes.
The first test on the FCS connected to the resistive load is run utilizing a
simplified R40 test cycle, with just three neat peaks, in order to obtain accelera-
tions phases in terms of current requirements of 5 A s
-1
and maximum power of
about 10 kW. The values of the air flow rate are preliminarily set in steady state
conditions for the whole load range comprised in the test cycle, in order to
guarantee a minimum power consumption of the air compressor compatible with
satisfactory values of the cell voltages. In particular, a control strategy for the
compressor was adopted choosing R values equal to 1.8 in the range 100-240 A,
and making them drop from 6 to 2 from open circuit to 100 A. In Fig.
7.14
, the
stack current and voltage measured during this test are reported as function of the
cycle length. The stack voltage reaches the minimum values of 63, 52, and 48 V
for the three current peaks of 80, 180, and 240 A, respectively. The R values
reproduce the steady state settings with minimum R = 1.8, while air flow rate
reaches 35 m
3
h
-1
at 240 A. The stack voltage profiles in Fig.
7.14
are in
agreement with data of the polarization curve obtained on the same stack, sug-
gesting that the dynamic of 5 A s
-1
does not compromise the regular stack
operation, as confirmed by the distribution of the individual cell voltages, shown in
Fig. 7.14 Stack voltage and
current versus time for a
dynamic test at 5 A s
-1
based
on the R40 cycle
80
500
70
60
400
50
300
Stack Voltage
Stack Current
40
30
200
20
100
10
0
0
0
50
100
150
200
Time [s]
