Have you been to the gas
station this week? Considering that we live in a very mobile
society, it's probably safe to assume that you have. While
pumping gas, you've undoubtedly noticed how much the price of
gas has soared in recent years. Gasoline,
which has been the main source of fuel for the history of
cars, is becoming more and more expensive and impractical
(especially from an environmental standpoint). These factors
are leading car manufacturers to develop cars fueled by
alternative energies. Two hybrid
cars took to the road in 2000, and in three or four years
cars will roll onto the world's highways.
Photo courtesy Zero Pollution
compressed-air engine is expected to make it an ideal
car for highly polluted cities.
While gasoline prices in the United States have not yet
reached their highest point ($2.66/gallon in 1980), they have
climbed steeply in the past two years. In 1999, prices rose by
30 percent, and from December 1999 to October 2000, prices
rose an additional 20 percent, according to the U.S. Bureau
of Labor Statistics. In Europe, prices are even higher,
costing more than $4 in countries like England and the
Netherlands. But cost is not the only problem with using
gasoline as our primary fuel. It is also damaging to the
environment, and since it is not a renewable resource, it will
eventually run out.
One possible alternative is the air-powered car.
There are at least two ongoing projects that are developing a
new type of car that will run on compressed air. In this
edition of How
Stuff Will Work, you will learn about the technology
behind two types of compressed-air cars being developed and
how they may replace your gas guzzler by the end of the
Two Cylinder Air-Compression Engine
Within the next two years,
you could see the first air-powered vehicle motoring through
your town. Most likely, it will be the e.Volution car
that is being built by Zero
Pollution Motors, in Brignoles, France. The cars have
generated a lot of interest in recent years, and the Mexican
government has already signed a deal to buy 40,000 e.Volutions
to replace gasoline- and diesel-powered taxis in the heavily
polluted Mexico City.
Photo courtesy Zero Pollution
The e.Volution will be
able to travel about 124 miles (200 km) before being
refueled with compressed air.
Makers of the e.Volution are marketing the vehicle as a low
pollution or zero pollution car. However, there is still some
debate as to what the environmental impact of these
air-powered cars will be. Manufacturers suggest that because
the cars run on air they are environmentally friendly. Critics
of the air-powered car idea say that the cars only move the
air pollution from the car's exhaust to somewhere else, like
an electrical power plant. These cars do require electricity
in order for the air to be compressed inside the tanks, and
fossil fuel power is needed to supply electricity.
The e.Volution is powered by a two-cylinder, compressed-air
engine. The basic concept behind the engine is unique (see this
page for details) -- it can run either on compressed air
alone or act as an internal combustion engine. Compressed air
is stored in carbon or glass fiber tanks at a pressure of
4,351 pounds per square inch (psi). This air is fed through an
air injector to the engine and flows into a small chamber,
which expands the air. The air pushing down on the pistons
moves the crankshaft, which gives the vehicle power.
Photo courtesy Zero Pollution
Exhaust from the
e.Volution vehicle's engine, seen here, will contain no
Zero Pollution Motors is also working on a hybrid version
of their engine that can run on traditional fuel in
combination with air. The change of energy source is
controlled electronically. When the car is moving at speeds
below 60 kph, it runs on air. At higher speeds, it runs on a
fuel, such as gasoline, diesel or natural gas.
Air tanks fixed to the underside of the vehicle can hold
about 79 gallons (300 liters) of air. This compressed air can
fuel the e.Volution for up to 124 miles (200 km) at a top
speed of 60 miles per hour (96.5 kph). When your tank nears
empty, you can just pull over and fill the e.Volution up at
the nearest air pump. Using a household electrical source, it
takes about four hours to refill the compressed air tanks.
However, a rapid three-minute recharge is possible, using a
high-pressure air pump.
The car's motor does require a small amount of oil, about
.8 liters worth that the driver will have to change just every
31,000 miles (50,000 km). The vehicle will be equipped with an
automatic transmission, rear wheel drive, rack and pinion
steering and a 9.5 foot (2.89 m) wheel base. It will weigh
about 1,543 pounds (700 kg) and will be about 12.5 feet (3.81
m) long, 5.7 feet (1.74 m) tall, and 5.6 feet (1.71 m) wide.
In October, the e.Volution made its public debut in
Johannesburg, South Africa, at the Auto Africa Expo
2000. Zero Pollution said that the car will go on sale in
South Africa in 2002, but didn't say when the car would be
available in other parts of the world.
Cryogenic Heat Engine
Another version of an
air-powered car is being developed by researchers at the University
of Washington using the concept of a steam
engine, except there is no combustion. The Washington
researchers use liquid nitrogen as the propellant for
their LN2000 prototype air car. The researchers decided
to use nitrogen because of its abundance in the atmosphere --
nitrogen makes up about 78 percent of the Earth's atmosphere
-- and the availablity of liquid nitrogen. There are five
components to the LN2000 engine:
The liquid nitrogen, stored at -320
degrees Fahrenheit (-196 degrees Celsius), is vaporized by the
heat exchanger. The heat exchanger is the heart of the
LN2000's cryogenic engine, which gets its name from the
extremely cold temperature at which the liquid nitrogen is
stored. Air moving around the vehicle is used to heat the
liquid nitrogen to a boil. Once the liquid nitrogen boils, it
turns to gas in the same way that heated water forms steam in
a steam engine.
- A 24-gallon stainless steel tank.
- A pump that moves the liquid nitrogen to the economizer.
- An economizer that heats the liquid nitrogen with
leftover exhaust heat.
- A heat exchanger that boils the liquid nitrogen,
creating a high pressure gas.
- An expander, which converts nitrogen's energy into
Nitrogen gas formed in the heat exchanger expands to about
700 times the volume of its liquid form. This highly
pressurized gas is then fed to the expander, where the force
of the nitrogen gas is converted into mechanical power by
pushing on the engine's pistons. The only exhaust is nitrogen,
and since nitrogen is a major part of the atmosphere, the car
gives off little pollution. However, the cars may not reduce
pollution as much as you think. While no pollution exits the
car, the pollution may be shifted to another location. As with
the e.Volution car, the LN2000 requires electricity to
compress the air. That use of electricity means there is some
amount of pollution produced somewhere else.
Some of the leftover heat in the engine's exhaust is cycled
back through the engine to the economizer, which preheats the
nitrogen before it enters the heat exchanger, increasing
efficiency. Two fans at the rear of the vehicle draw in air
through the heat exchanger to enhance the transfer of heat to
the liquid nitrogen.
The Washington researchers have developed a crude prototype
of their car, using a converted 1984 Grumman-Olson Kubvan mail
truck. The truck has a radial five-cylinder that produces 15
horsepower with the liquid nitrogen fuel. It also features a
five-speed manual transmission. Currently, the vehicle is able
to go only about two miles (3.2 km) on a full tank of liquid
nitrogen, and its top speed is only 22 mph (35.4 kph).
However, because a liquid nitrogen-propelled car will be
lighter, the researchers think that a 60-gallon (227 liters)
tank will give the LN2000 a potential range of about 200 miles
With gas prices soaring, as they have over the past two
years, it might not be long before many motorists turn to
vehicles powered by alternative fuels. Although air-powered
vehicles are still behind their gasoline counterparts when it
comes to power and performance, they cost less to operate and
are arguably more environmentally friendly, which makes them
attractive as the future of highway transportation.
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