Only about 15% of the energy from the fuel you put
in your tank gets used to move your car down the road or run useful
accessories, such as air conditioning. The rest of the energy is
lost to engine and driveline inefficiencies and idling. Therefore,
the potential to improve fuel efficiency with advanced technologies
is enormous.
The diagram above shows typical
energy uses and losses in a vehicle.
Click on any of the uses or
losses above to learn more.
Engine Losses
– 62.4%
In gasoline-powered vehicles, over 62%
of the fuel's energy is lost in the internal combustion
engine (ICE). ICE engines are very inefficient at
converting the fuel's chemical energy to mechanical
energy, losing energy to engine friction, pumping
air into and out of the engine, and wasted heat.
In addition, diesels
are about 30-35% more efficient than gasoline engines,
and new advances in diesel technologies and fuels
are making these vehicles more attractive.
Idling Losses
– 17.2%
In urban driving, significant energy
is lost to idling at stop lights or in traffic. Technologies
such as integrated
starter/generator (ISG) systems help reduce these
losses by automatically turning the engine off when
the vehicle comes to a stop and restarting it instantaneously
when the accelerator is pressed.
To move forward, a vehicle's drivetrain
must provide enough energy to overcome the vehicle's
inertia, which is directly related to its weight.
The less a vehicle weighs, the less energy it takes
to move it. Weight can be reduced by using lightweight
materials and lighter-weight technologies (e.g., automated
manual transmissions weigh less than conventional
automatics).
In addition, any time you use your brakes,
energy initially used to overcome inertia is lost.
Rolling Resistance
– 4.2%
Rolling resistance is a measure of the
force necessary to move the tire forward and is directly
proportional to the weight of the load supported by
the tire. A variety of new technologies can be used
to reduce rolling resistance, including improved tire
tread and shoulder designs and materials used in the
tire belt and traction surfaces.
For passenger cars, a 5-7% reduction
in rolling resistance increases fuel efficiency by
1%. However, these improvements must be balanced against
traction, durabillity, and noise.
Aerodynamic
Drag – 2.6%
A vehicle must expend energy to move
air out of the way as it goes down the road—less
energy at lower speeds and progressively more as speed
increases. Drag is directly related to the vehicle's
shape. Smoother vehicle shapes have already reduced
drag significantly, but further reductions of 20-30%
are possible.
Accessories – 2.2%
Air conditioning, power steering, windshield wipers,
and other accessories use energy generated from the
engine. Fuel economy improvements of up to 1% may
be achievable with more efficient alternator systems
and power steering pumps.