Environmental Engineering Reference
In-Depth Information
burning diesel fuel and gasoline-electric hybrids. CV power plants currently
have less than 30% thermal efficiency. At the far right in Figure 1.19 are fuel cell
power plants, assuming on-board storage of hydrogen, for which virtually no
weight reduction is necessary in order to sustain CV performance. Lighter weight
hybrid vehicles should maintain the performance, size, utility and cost of ownership
of CVs.
1.4.3 Drive cycle characteristics
Further performance criteria revolve around steering, braking, ride and handling
and their enhancements possible with vehicle stability programmes. The hybrid
functions are consistent with environmental imperatives of reduce, reuse and
recycle. Reduction of fuel consumption implies not to burn fuel when the vehicle
is not being propelled. Reuse and recycle imply recuperation of fuel energy
already spent.
Idle-stop functionality is the primary means of fuel consumption reduction and
is implemented as a strategy stop of the engine. Extensions to fuel consumption
reduction consist of early fuel shut off and deceleration fuel shut off (DFSO). In
these cases engine fuelling is inhibited while the vehicle is still in motion. Early
fuel shut off in general means the engine will not idle during a downhill coast, for
example. DFSO means that fuel delivery to the engine is inhibited when the engine
speed drops below 600 rpm to perhaps 1,200 rpm depending on ride and drive
performance such as when approaching a stop. Fuel economy advantages of idle-
stop range from 5% for mild hybrids to 15% with high electric fraction and DFSO.
Fuel economy benefit ranges depend strongly on the particular drive cycle, or
customer usage pattern. In order to standardize customer driving patterns and
usage, various regions and governments have defined standard drive cycles. In
North America the Environmental Protection Agency (EPA) has defined several
cycles including EPA-city, EPA-highway, EPA-combined and others. Europe,
for example, now uses the New European Drive Cycle (NEDC). In Japan, because
of the dense urban driving, a 10-15 mode has been defined that captures the
high percentage of idle time spent. These standard drive cycles are summarized in
Table 1.8 along with some useful statistics.
Table 1.8 Standard drive cycles and statistics
Region
Cycle
Time
idling (%)
Max. speed
(kph)
Average speed
(kph)
Maximum
accl. (m/s
2
)
Asia-Pacific
10-15 mode
32.4
70
22.7
0.79
Europe
NEDC
27.3
120
32.2
1.04
NA-city
EPA-city
19.2
91.3
34
1.60
NA-highway
EPA-hwy
0.7
96.2
77.6
1.43
NA-US06
EPA
7.5
129
77.2
3.24
Industry
Real world
20.6
128.6
51
2.80
