Environmental Engineering Reference
In-Depth Information
The relationships in (1.31) are reciprocal, so L/100 km and mpg are inter-
changeable. For example, 18 mpg is 13.07 L/100 km. This conversion is in absolute
terms and good for characterizing the overall fuel economy or fuel consumption of
a vehicle. Hybrid propulsion advantages are characterized by their incremental
benefit over a baseline vehicle. The baseline fuel economy or fuel consumption
being known quantities, the goal is to characterize the benefits of hybrid
improvements as a percentage. To make this conversion, the following relation-
ships are necessary:
FE hybrid
FE base
FE base
FE hybrid
FE base 1
%FE benefit ¼
¼
ð 1 : 32 Þ
Equation (1.32) states the fuel economy benefit of hybrid actions relative to the
base vehicle fuel economy. Conversion between fuel economy and consumption is
given as (1.33):
100
100 þ %FE benefit
%FC benefit ¼ 100 1
ð 1 : 33 Þ
For example, if the base vehicle fuel economy is 27.5 mpg and hybrid actions
such as idle-stop incur a fuel economy benefit of 7%, then (1.33) predicts this same
action is worth a fuel consumption benefit of 6.54%. Conversely, this same vehicle
having 8.55 L/100 km fuel consumption may receive a benefit of 8% on the Eur-
opean drive cycle for idle-stop hybrid actions. To compute the equivalent fuel
economy improvement, (1.33) is solved for fuel economy benefit and becomes
%FC benefit
100 %FC benefit
%FE benefit ¼ 100
ð 1 : 34 Þ
Solving the example stated using (1.33) yields a fuel economy benefit of 8.7%.
Figure 1.30 illustrates the conversion of fuel economy to fuel consumption benefit
described in (1.32-1.34).
From Figure 1.30 one can notice that a 100% fuel economy benefit amounts to
a fuel consumption reduction of 50%. The conversion is non-linear and is shown
for US fuel economy in mpg. The conversion would require an adjustment for
conversion to Imperial gallons (see (1.31)).
1.7
Internal combustion engines: A primer
Internal combustion engines operate on the open chamber process in which the
exchange of the working mixture must fulfil two functions: (1) the gas mixture is
returned to the initial condition of the cycle through exchange and (2) the oxygen
necessary for combustion is provided in the form of induction air. In a four stroke
engine, the gas exchange frequency is regulated by the camshaft operating the val-
ves at half the frequency of the crankshaft that drives it. When the intake valve
opens, a fresh gas mixture is inducted into the chamber by atmospheric pressure.
Search WWH ::




Custom Search