Environmental Engineering Reference
In-Depth Information
Fig. 6.7 Power losses asso-
ciated with the main fuel cell
system components versus
DC-DC converter inlet
power under the experimental
conditions of Fig.
6.4
air compressor (about 120 W, when the FCS generates a power of 1.8 kW), while
minor losses are related to the cooling and humidification of water pump (about
10 W each and constant with respect to the load). Further energy consumptions are
due to cables connecting the FCS to DC-DC converter (about 80 W at the highest
load) and undetermined system losses, measures as about 20 W when the stack is
off and about 70 W when is switched on, and depending on several electric
components, necessary in a FCS designed for laboratory tests, such as sensors,
electric valves, wires, induction relays, and electronic control boards.
The consumption of these last auxiliary components might be partially reduced
with a specific design of the FCS for a real vehicle, but the energy losses due to the
air and water management system would be quite difficult to be lowered. In this
respect, the maximum FCS efficiency (55% at medium load, see Fig.
6.6
) takes in
regards to the only loss sources due to the air compressor, hydrogen purge, and
water pump.
6.4 Dynamic Performance of the FCS
The dynamic behavior of the FCS is firstly verified starting from the analysis of the
energy lost during the start-up phases, evaluating the performance as function of
acceleration rates [
2
]. In particular, warm-up tests are performed starting from two
different initial stack temperatures, 15 and 30C. For each one of these tempera-
tures, two accelerations of 20 and 200 Ws
-1
are used up to the stack power of
1200 W. At the end of each acceleration phase, a steady-state operation follows
until the stack temperature reaches the value of 45C.
Other dynamic tests are affected varying the stack power and evaluating the
stack response to hydrogen purge, external humidification, and air management
