Environmental Engineering Reference
In-Depth Information
Example 2:
Assuming this acceleration is constant, what is the dragster's speed
when
d
= 100 ft?
Solution:
Using the relations given in Example 1 the time for the dragster to cover
100 ft can be found to be 1.205 s. Speed is the integral of acceleration, so the
velocity at
T
= 1.205 s is given by
r
2
d
a
r
60
:
8
41
:
86
ð
T
ð
1
:
205
V
100
¼
T
¼
¼
¼
1
:
205 s
;
adt
¼
41
:
86
dt
¼
50
:
45m
=
s
0
0
The dragster's speed at 100 ft is therefore 50.45/0.447 = 112.8 mph!
3.1 Grade and cruise targets
In order to assess the vehicle performance on grades and during cruise, a repre-
sentative vehicle is selected to carry out the analysis. Here, the Ford Focus is used
since it represents a mid-sized vehicle capable of comfortably carrying four pas-
sengers and meeting customer expectations on performance and economy. For this
class of vehicle, 0-60mph acceleration performance in the 9-12 s range is ade-
quate. Table 3.3 summarizes pertinent attributes for the Focus 5-door, 4-passenger,
mid-size passenger car.
Table 3.3 Passenger vehicle attributes
Vehicle attribute
Value
Curb weight, kg
1,077
Gross vehicle weight, kg (fully loaded vehicle limit)
1,590
Frontal area, m
2
(length: 4.178 m
height: 1.481 m - ground clearance)
2.11
Aerodynamic drag coefficient,
C
d
0.335
Acceleration time, 0-60 mph, seconds (0-100 kph) with 1.8 L Zetec
(4 V, DOHC, 85 kW at 5,500 rpm, 160 Nm at 4,400 rpm)
10.3
Elasticity, 30-60 mph, seconds (in fourth gear for passing, lane changing)
13.5
Maximum vehicle speed, mph/kph
124/198
Fuel consumption, L/100 km (on NEDC cycle) Specific fuel consumption,
min: 230 g/kWh
7.5
Emissions, g CO
2
/km
181
G
src
, gear shift ratio coverage (1st/4th) transmission, 4-speed automatic
1st 2.816:1, 2nd 1.498:1, 3rd 1.000:1, 4th 0726:1, FD 3.906:1
3.88
r
w
,
m
, rolling resistance of P185/65 R 14 tyres. Tyre code: P = passenger,
W
section
= 185 mm,
c
= aspect ratio = 65%, R = speed rating, rim OD = 14 in.
0.285
The dynamic rolling radius of the vehicle's tyres is computed according to
(3.1), given the adjustment factor taking static unloaded radius to dynamic loaded