Environmental Engineering Reference
In-Depth Information
17.2%
Aerodynamic
Drag
2.6%
Rolling
Resistance
4.2%
Standby/Idling
2.2%
Accessories
1
18.2%
1
Drive Line Losses
Inertia
Braking
5.8%
Engine Losses
5.6%
62.4%
flows for a
vehicle powered by an internal combustion engine. The diagram
shows the energy uses and losses from a typical vehicle.
(Source: fueleconomy.gov)
fig. 11.4
Where does the energy go? How energy
further third is lost in getting through the transmission,
drive train, and differential (there is almost no difference
in the loss between front-wheel and rear-wheel drive
cars). The
% that actually moves the vehicle goes to
overcoming aerodynamic drag and rolling resistance, and
to braking losses when slowing.
Aerodynamic drag depends on the design of the vehicle
and the speed; the
.
% loss to aerodynamic drag is an
average. Rolling resistance depends on tire design and
pressure. Under-in
.
ation can cost considerably in fuel
economy (sorry to say there are ignorant politicians who
ridicule this notion). The remaining part of the energy
delivered to the wheels goes to accelerate the vehicle to its
operating speed and is lost to heat in the brakes when
speed is reduced. Typically, fuel economy is lower in city
driving than in highway driving. The main contributor to
the reduction for city driving is the more frequent stops
