Environmental Engineering Reference
In-Depth Information
The conversion to fuel economy is given by
V
BSFC
g
fuel
FE
¼
8
;
467
:
93
P
eng
ð
mpg
Þ
ð
1
:
30
Þ
where vehicle speed,
V
, is in mks units of m/s, specific fuel consumption
BSFC is given as g/kWh, specific gravity is in g/cm
3
and engine power is in kW.
Figure 1.28 illustrates the relationship of BSFC to
P
eng
for an ISA/ISG hybrid
installation.
Engine power vs.
vehicle weight class
10 kW/125 kg
kW
Nm
200
180
160
100
80
60
kg/kWh
0.32
0.30
0.28
2,000
4,000
8,000
Engine speed (rpm)
Figure 1.28 Performance curves: engine torque, power and BSFC versus speed
The torque curve versus speed for a CIDI engine will be flatter than the cor-
responding SI engine and it will have a more restricted operating speed range of
typically 4,500 versus 7,000 rpm. The fuel map of a CIDI engine, the 1.8 L direct
injected, Endura DI shows very broad fuel islands below 240 g/kWh, which yield
excellent fuel consumption results [15]. In the Focus vehicle the Endura 1.8 L CIDI
engine achieves 4.9 L/100 km on the combined cycle.
An explanation of brake mean effective pressure (BMEP) used in Figure 1.29
is given in Section 1.7.1. The optimal fuel trajectory is shown as the heavy dotted
trace representing power output at lowest fuel consumption. The Endura 1.8 L CIDI
engine is rated 66 kW at 4,000 rpm and 200 Nm torque at 2,000 rpm. The engine
weights 158 kg (0.42 kW/kg) and has a compression ratio of 19.4:1.
1.6.3 Fuel economy and consumption conversions
All of the factors that must be considered in a derivation of fuel economy are listed
in Table 1.14. Each factor has a direct impact on fuel economy and some an
