Environmental Engineering Reference
In-Depth Information
Chapter 4
Design of Hydrogen Fuel Cell Systems
for Road Vehicles
A fuel cell stack does not work by itself, but its operation requires the utilization of
several auxiliary sub-systems to permit an efficient and reliable electric power
production. In this chapter all these components are described, evidencing their
role in determining the fuel cell stack operation. In particular, this discussion is
aimed at verifying if and how a fuel cell system (FCS) could really match all
vehicular requirements, evidencing the parasitic losses of auxiliary components
and dynamic performance in terms of response to start-up, frequent stop and go
phases, fast load changes, variable power levels. The interaction between FCS
performance and management strategies necessary to guarantee an optimal stack
operation in automotive applications is discussed, with a brief overview of FCS
costs.
Several models of FC vehicles fuelled by H
2
have been produced by many car's
industries in the past two decades, characterized by interesting performance and
promising reliability (i.e., Mercedes-Benz presented at the end of 2009 the new
model B class F-Cell equipped with new generations of fuel cells, Li-ion batteries,
and advanced fuel storage tanks). Other solutions with the stack fed with liquid
fuels (methanol, gasoline, and diesel) have been also proposed, but they require an
on-board fuel processor to transform the liquid mixture into hydrogen. In this case
the impact of the fuel processor on the choice of the hybridization level for the
whole propulsion system (see
Sect. 5.5
) and on stack durability needs to be
carefully considered. Dynamic response of FCS with processor unit would be too
slow mainly because of its thermal inertia, implying that the stack has to operate
almost in steady state conditions, while the unavoidable presence of some com-
pounds in reformer outlet stream, such as CO or NH
3
, also in very low concen-
trations, are dangerous contaminants for the activity of stack electrodes. Recently
it has been estimated that start-up time would be less than 4 min to lower the CO
level present in the stream at acceptable values [
1
], but long-term durability of
stacks fed by reformate stream is far to be demonstrated.
