Environmental Engineering Reference
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gine, aerodynamic drag, rolling resistance of tires, transmission slippage,
internal friction, idling and air conditioning.
Large frontal areas create air turbulence and drag and bodies de-
signed from wind tunnel testing can provide a more smooth air flow
around the vehicle. Automatic transmissions impose a mileage penalty
of about 10% compared to manual gearboxes and continuously variable
transmissions could provide better mileage. A stop-start engine that shuts
down if a car is idling or coasting can cut gas consumption by about 15%.
This is what happens in a hybrid vehicle as they shift to electric drive.
Better lubricants and bearings are reducing friction and micropro-
cessors monitor engine conditions and make adjustments to keep opera-
tion at peak efficiency without actions by the driver.
As the price of petroleum for gasoline and diesel engines converg-
es with that of alternate energy sources, new power systems will become
more widely used. Battery-powered electric motors are quiet with low pol-
lution and simplicity, the disadvantages of limited range between recharges
(which are also limited), weight, and bulk reduce their market potential.
New battery systems could give better performance but they have
not been forthcoming. Performance is limited by the lead-acid battery
packs which are generally the most affordable option. More unfamiliar
batteries like nickel metal hybride (NiMH) packs have also appeared.
The common 12-volt lead-acid battery has six cells, each contain-
ing positive and negative lead plates in an electrolyte solution of sulfuric
acid and water. This proven technology is not expensive to manufacture
and it's relatively long-lasting. But, the energy density of lead-acid bat-
teries, the amount of power they can deliver on a charge, is poor when
compared to NiMH and other newer technologies. The United States
Advanced Battery Consortium (USABC) is a Department of Energy pro-
gram launched in 1991. Since 1992, USABC has invested more than $90
million in nickel metal hybride batteries.
These batteries are much cheaper to make than earlier nickel battery
types, and have an energy density almost double that of lead-acid. NiMH
batteries can accept three times as many charge cycles as lead-acid, and
work better in cold weather. NiMH batteries have proven effective in lap-
top computers, cellular phones, and video cameras.
NiMH batteries can power an electric vehicle for over 100 miles,
but are still several times more expensive than lead-acid. NiMH batter-
ies from Energy Conversion Devices were installed in GM's EV
I
and S-10
electric pickup truck, doubling the range of each. Chrysler has also used
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