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How Air-Powered Cars Will Work
by Kevin Bonsor


Photo courtesy Zero Pollution Motors
The e.Volution's compressed-air engine is expected to make it an ideal car for highly polluted cities.
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 fuel-cell-powered cars will roll onto the world's highways.

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 decade!

Two Cylinder Air-Compression Engine

Photo courtesy Zero Pollution Motors
The e.Volution will be able to travel about 124 miles (200 km) before being refueled with compressed air.
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.

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 Motors
Exhaust from the e.Volution vehicle's engine, seen here, will contain no pollutants.

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:

  • 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 usable power.
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.

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 (321.8 km).

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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