Environmental Engineering Reference
In-Depth Information
Chapter 7
Case Study B: Fuel Cell Power Train
for Cars
7.1 Description of the 30 kW Fuel Cell Power Train
Figure
7.1
a-c shows the three main sections of a laboratory plant specifically
designed for characterization of a 20 kW PEM stack, which was chosen to supply
the electric drive for road vehicles analyzed in this chapter.
These sections include: hydrogen feeding, air feeding with humidification, and
stack cooling systems. The stack specifications and detailed technical character-
istics of the auxiliary components, with all the mechanical and electric devices
necessary for stack operation, are reported in Table
7.1
.
The fuel feeding system is reported in Fig.
7.1
a. High purity hydrogen or
nitrogen, necessary for the cell and hydrogen pipeline purge, are fed by high
pressure cylinders (200 bar), while a pressure reduction stage (7 bar maximum) is
installed at the hydrogen inlet.
For all the experimental tests the PEM stack operates in dead end configuration,
i.e., the anodic compartment is maintained closed and pressurized. A purge electric
valve is placed at the hydrogen line outlet to drain the excess of water diffusing
zfrom the cathode to the anode side through the polymeric membrane (see
Sect. 4.2
).
Hydrogen flow rate is calculated by the current drawn, taking into account the
amount of hydrogen purged. Defining a fuel utilization coefficient (g
util
)asratio
between the mass of fuel reacted in the stack and the mass of fuel entering the stack,
it was preliminary fixed at 0.90 according to indications of the stack manufacturer.
This value can be experimentally set by pre-defining the opening time and frequency
of the anode purge valve, and measuring the purged volume.
The air management system is shown in Fig.
7.1
b. A side channel compressor is
used for low pressure experiments (below 130 kPa), while a centralized air
compression plant is used to study the effect of air pressure on stack performance
(between 130 and 250 kPa). An important issue to be considered is the cell humid-
ification to guarantee that the stack works properly, since the electrolyte membrane
needs to be continuously hydrated (see
Sects. 3.2
and
4.5
). That humidification is
