Environmental Engineering Reference
In-Depth Information
600
At standard mapping point
ISFC
500
400
300
BSFC
200
0 1 2 3 4 5 6 7 8 9
BMEP
Figure 1.33 Fuel consumption versus BMEP
9
At standard mapping point
8
7
6
IMEP
5
4
BMEP
3
2
1
0
0
1
2
3
4
5
6
7
8
9
BMEP
Figure 1.34 MEP versus BMEP
To further illustrate the point made in connection with Table 1.14 that trans-
mission gear step selection and overall gear shift ratio coverage impact fuel econ-
omy, it is worthwhile noting the relationship of BSFC to engine speed at constant
power output. BSFC is a monotonic function of engine speed at constant power and
a large reason why fuel economy over a given drive cycle is so dependant on
powertrain matching (gear sizing and ratio coverage). Figure 1.35 illustrates the
trend for the Focus engine discussed earlier at three output points: 5, 10 and 15 hp.
