Environmental Engineering Reference
In-Depth Information
Fig. 7.13 Stack and FCS
electric efficiencies versus
stack current at T = 313 K
Then, the system based on the bubbler does not appear as the most convenient
solution. A system based on electronic injection of water into the cathode inlet
manifold, whose action depends on the uniformity of the individual cell voltages,
could be the most effective technique for automotive applications. This solution
would involve the use of an injection pump, which, however, would not affect
significantly the FCS electric efficiency shown in Fig.
7.12
. Another not pre-
dominant contribution to the energy losses due to the FCS auxiliary components
can be identified in the electric consumption of the fan/radiator, which is useful to
control the cooling water temperature on board of a vehicle [
3
].
7.3 Analysis of the Dynamic Behavior of the FCS
The interaction between stack and its auxiliary components in dynamic conditions
has to be investigated to obtain indications about the possibility to adopt hybrid
configurations that require fast load variations of the FCS (up to 6 kW/s). The
hydrogen purge, external humidification, stack temperature, and stoichiometric
ratio have to selected with the aim of individuating working strategies able to
assure reliable operation in dynamic conditions. Moreover, the transient perfor-
mance of the FCS have to be analyzed during warm-up phases, which are char-
acterized by similar acceleration slopes (6 kW/s).
This experimental analysis can be carried out on the FCS connected to a var-
iable resistive load by means of the DC-DC converter, which is controlled to
simulate the instantaneous current requests of electric drive. The tests described in
the following are performed varying the slope of the acceleration phases, between
5 and 50 A s
-1
, on the base of the stack current requirements. For each working
condition, the uniformity of individual cell voltage during the transient step is
assumed as indicator of stack operation reliability.
