Environmental Engineering Reference
In-Depth Information
energy benefit requires that parallel hybrid, gasoline-electric power plants be
carefully thought out in order to justify a business case. The Prius power-split
hybrid, on the other hand, shows near parity with the gaseous hydrogen fuel cell
power plant. Here again is an indicator that a strong business case is necessary
when selecting any particular hybrid architecture over any other, or a fuel cell, for
that matter.
The results on vehicle energy consumption given in Figure 9.4 must be taken
within proper context. The survey of global energy consumption for the various
driveline configurations and power plant technologies will each perform differently
in different regulated cycle drives. One architecture and power plant configuration
may indeed have a significant benefit over another for a given drive cycle, but
switch to a different drive cycle and the results may be surprising. It is no surprise
then that vehicle fuel consumption is strongly dependent on drive cycle, but what is
not readily apparent is that hybrids may in fact not be graded on drive cycles that
properly reflect their customer usage.
Cunningham
et al.
[7] look at the direct hydrogen hybrid, or FCHV, versus a fuel
cell power plant load tracking power plant, or FCV. In this comparison, it is observed
that hybridizing an FCV will not have as significant a gain as hybridizing a con-
ventional gasoline ICE vehicle. The load following FCV relies strictly on hydrogen
feed and air control to deliver acceptable transient performance. The FCHV, on the
other hand, uses battery assist to deliver transient events. It was found in Reference 7
that the hybrid vehicle had generally better results over the FCV on most of the drive
cycles, except Highway. Table 9.2 summarizes these results.
Table 9.2 FCHV versus FCV economy comparisons (from
Reference 7)
Economy (kWh/mi)
% Difference FCHV vs. FCV
Highway
0
US-combined (M-H)
8.3
Federal Urban Drive Schedule (FUDS)
14.5
US06 (aggressive or real world)
15.1
New European Drive Cycle (NEDC)
8.3
Japan urban cycle, 10-15 mode
9.5
The hybrid vehicle fares best on drive cycles with more stop-go driving as well
as more frequent stops. Overall, the FCHV realized better fuel consumption than
its load tracking fuel cell sister vehicle on all drive cycles. It is curious that the
degree of separation between the two fuel cell architectures was not so dramatic on
the Japan cycle, which has low average speed, compared to similar performance
on the US Highway and European NEDC cycles, which have significantly higher
average speeds. Table 9.3 summarizes the average speeds of these cycles.
