Nitrogen needs to be kept cold in order to stay in liquid form. When released into a car engine, the nitrogen is then heated and expands to create energy. The expanding nitrogen powers turbines the same way combustion in a gasoline-powered engine moves pistons. Nitrogen is abundant in our atmosphere and cars powered by it don't create as many harmful emissions as gas and diesel do, but they're not really viable because there's no network of nitrogen fueling stations in America.
Among the notable attempts at creating a nitrogen-powered car concerned work done at the University of Washington in the late 1990s on the LN2000, a prototype vehicle that used the body of a mail truck and was powered by -- you guessed it! -- liquid nitrogen. The team asserted that to create a truly non-polluting car, inventors had to move away from electric and gasoline power sources. So they built the LN2000, which worked like a steam engine, except that the power came not from the steam of boiling water but from the vaporization of cold liquid nitrogen. True, any plant that would be used to create liquid nitrogen would likely be run on fossil fuel, but the car's developers recognized the trade-off could be acceptable [source: Orwig].
Another nitrogen-powered car was developed around the same time at the University of North Texas, using a cryogenic heat engine driven by liquid nitrogen. The no-emission car was called the CoolLN2Car, and the interesting thing about the cryogenic engine was that its fuel source could be either liquefied air or liquid nitrogen. You get liquefied air by grabbing air from the atmosphere and cooling and compressing it. Liquid nitrogen takes a similar approach with nitrogen gas. Using liquefied air, air is heated and expanded, only without using combustion, which would pollute the air. So, in essence, the car ran clean exhaust [source: Univ. of North Texas].
While science and society have yet to see a highway full of nitrogen-powered cars as of yet, it's a safe bet such ideas won't be abandoned.
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