Environmental Engineering Reference
In-Depth Information
4.2 Hydrogen Feeding System
The layout of the fuel feeding sub-system and its management strategy depends on
the typology of fuel tank installed on-board. For any type of hydrogen storage
system (see
Sect. 2.3
), the main parameters to be controlled in hydrogen feeding
sub-systems are: working pressure, relative humidity, fuel purity grade, and fluid-
dynamic conditions.
Hydrogen can be supplied either in dead-end or in a flow-through mode. The
choice of feeding pure hydrogen as fuel, rather than hydrocarbon derived hydrogen
mixtures, permits the choice of the so-called ''dead-end'' configuration as option
of fuel feeding. In this case hydrogen is loaded to the stack as pressurized gas,
thanks to a valve normally closed placed at the outlet. It means that the current
supplied by the stack determines the occurrence of a fuel flow rate through the
anode channels, exclusively related to the power required. On the other hand, the
hydrogen flux stops in the absence of load. This solution needs generally a purge
valve to drain out the possible excess of nitrogen and water accumulated in the
anode side during stack operation. This valve is generally an electronic controlled
solenoid valve. An alternative operative mode, suitable also if fuel cell vehicle is
equipped with a fuel reformer, is represented by the so-called ''flow-through''
configuration. This option requires additional components such as hydrogen
recycle pump or ejectors. The choice between the two configurations affects the
design of the specific sub-system and could influence its integration with the other
FCS components.
A scheme of a fuel feeding sub-section in a direct hydrogen FCS for automotive
application is shown in Fig.
4.2
. Pressure regulation sub-system design has the
objective to regulate inlet pressure to assure the hydrogen flow rate necessary to
the chemical reaction. The inlet pressure and fuel purge represent the main
parameters to be controlled in both operative modes, however, the role of the
purge valve is different for the two possible configurations. In a dead-end con-
figuration and when air is used as oxidant, nitrogen tends to crossover from the
Fig. 4.2 A scheme of a
generic pure hydrogen
feeding sub-system in
flow-through mode. Without
ejectors the same scheme
refers to dead-end mode
1: On-off valve
2: Pressure regulator
3: Proportional valve
4: Pressure transducer
5: Stack
6: Ejectors at high and
….
low flow
7: Purge valve
4
1
2
3
6
6
5
H
2
tank
7
