Environmental Engineering Reference
In-Depth Information
wear because the test dates are several weeks apart, some due to warmer ambient
conditions, but the remainder of environmental conditions are the same: no wind,
same stretch of highway and consistent testing methodology. We also rule out the
well known fact that rolling resistance is sensitive to vehicle speed as was shown by
testing results made at the University of Michigan Transportation Research Insti-
tute for heavy truck tyres [5]. In that reference a dynamic rolling resistance con-
tribution is characterized as follows:
F
tyre
¼
c
hwy
ð
R
0
þ
R
1
V
Þ
F
bias
-
ply
¼
c
hwy
ð
R
0
b
þ
R
1
b
V
Þ
N
Þ
F
radial
¼
c
hwy
ð
R
0
r
þ
R
1
r
V
Þ
ð
11
:
13
Þ
where
c
hwy
¼
(1.0 smooth concrete, 1.2 worn concrete, 1.5 hot asphalt) and
the static and dynamic rolling resistance coefficients are:
R
0
b
¼
0.004,
R
0
r
¼
0.007,
R
1
b
¼
0.004 and
R
1
r
¼
0.000046. From this characterization we would not expect to
see a shift in coast down tests between empty and loaded trailer because the testing
procedure is performed on the same road and at the same speeds using the same
tyres unless the tyre coefficients are load dependent. The conclusion here is that the
tyre wear apparently causes the shift in static rolling resistance to a somewhat lower
value. The effect is compounded by warmer ambient temperatures.
Regulations pertaining to OTR trucking are now changing with some states
requiring non-idling at rest stops and elsewhere. Infrastructure changes include
installation of shore power at rest stops and terminals. Some installations of shore
power requirements are already in place and non-idling may soon be regulated.
Military line haul and commercial OTR trucks are also being targeted for dedicated
auxiliary power units for providing power for all accessories during engine-off
periods. Various technologies from fuel cells to free piston engines are being
evaluated as electric power cells rated at 5 kW for powering cabin climate control
and accessories during overnight parking. In Reference 6, Algrain
et al.
describe a
programme to electrify a class-8 tractor through inclusion of a crankshaft mounted
starter-alternator that supports electric driven water pump, oil pump, air com-
pressor for brakes and modular air conditioning module for cabin climate control.
In addition, the electrification effort includes an on-board APU rated 8 kW at
340 V
dc
. The APU is driven by a small, two-cylinder, 0.5 L CIDI engine
rated 14 Hp at 3,600 rpm. A shore power module supplies dc bus voltage from a
120/240 V, 60 Hz input. The truck 12 V battery(s) is (are) maintained during non-
idling load periods through a dc/dc converter having input power delivered from
either the shore power connection or the APU. The starter-alternator for a large
displacement (15 L CIDI) engine is a package,
f
360
L
125 mm, which is
rated 1,200 Nm cranking torque and generates 15 kW at 600 rpm idle and 28 kW at
1,200 rpm. The fuel economy gained through use of the non-idling electrification is
projected at 7.5% (plus an additional 4.5% from the APU) and a potential for 1%
additional through electrified accessories. Considering that the North American
population of class-8 rigs is 458,000, it can be seen that the fuel savings amount to
