similarly broken apart into the greenhouse gases H 2 O and CO 2. Catalytic converters only
work when they are hot, so a lot of exhaust escapes as the car is warming up.
Figure 22.12: A large catalytic converter on an SUV. ( 11 )There are several simple ways to make a vehicle more fuel efficient. Lighter vehicles need less
energy to move. Streamlined vehicles experience less resistance from the wind. So, small,
lightweight, streamlinedcarsgetmuchbettergasmileagethanchunky, heavySUVs.Hybrid
vehiclesare among the most efficient vehicles that are now widely available. Hybrids have
a small internal combustion engine that works like an ordinary car. They also have an
electric motor and a rechargeable battery. During braking, a normal car loses the energy
it has because it is in motion. In a hybrid, that energy is instead funneled into charging
the battery. When the car accelerates again, it uses the power stored in the battery. The
internal combustion engine only takes over when power in the battery has run out. Hybrids
get excellent gas mileage in cities where the vehicle frequently stops and starts. Hybrid
vehicles also have catalytic converters: the battery preheats the converter so that it begins
to work much sooner after the car is turned on. Hybrids can reduce auto emissions by 90%
or more. Unfortunately, in many hybrid vehicles the hybrid technology is used to improve
acceleration more than gas mileage.
A new technology that is in development is a plug-in hybrid. The vehicle is plugged into an
electricity source when it is not in use, perhaps in a garage. The car uses the power stored
in that battery when it is next used. Plug-in hybrids are less polluting than regular hybrids,