Environmental Engineering Reference
In-Depth Information
Figure
b
, however, shows a dramatic change in the
weight and acceleration of vehicles. The weight
.
rst went
down to help meet the standards (a
% weight reduction
results in a
% mpg increase) and then went up steadily
from
to
. Times for acceleration from a stop to
mph went dramatically down over the same period. To
do this without reducing fuel economy required a major
increase in engine ef
ciency. The auto makers knew per-
fectly well how to do it, but when the price of oil crashed
down in
, customers no longer demanded more fuel
economy, so improved ef
ciency went into performance
and increasing the size of vehicles rather than improving
fuel economy. Only government regulations held mpg
steady. If you look hard you can
find many articles in
the late
s arguing that it was un-American to restrict
the kind of cars people could buy by restricting fuel
economy. Fortunately, the government did not listen,
for if they had US oil imports would be much larger than
they are today.
The average energy ef
ciency of a typical car with a
gasoline-powered internal combustion engine (ICE) is
very low.
Figure
is from the US Environmental
Protection Agency and shows where the energy in the
gas tank goes.
What is called the
.
ciency is the
fraction of the energy in the gasoline that actually moves
the car. In the standard ICE car it is a low
“
tank-to-wheels
”
ef
.
%. More
than
% of the primary energy is lost in the engine to
friction and heat,
% goes to
operate accessories such as lights, air conditioning, and
radios. Only about
% is lost to idling, and
% of the primary gasoline energy is
delivered to the output of the engine and from there a
