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Are Nitrogen Powered Cars The Future?
_Chainsaw writes: "The local paper ran this story about a retired engineer who has come up with the concept of nitrogen powered cars. The idea is that the pressure generated when liquid nitrogen is changed into a gas state via a heat exchanger could power a car. What are the pros and cons of this idea versus conventional gas-powered cars and the ideas of battery powered and fuel cell powered cars? Safety issues? In the event of an accident is being flash-frozen better than being burned to death or dissolved by battery acid? What is the environmental impact of letting tons of nitrogen a day escape into the atmosphere?" I wonder how easy it is to keep the nitrogen cold, too. It's interesting to consider what things will look like in 50 or 100 years, though. Will cars still be the dominant form of transport for Americans? Will Nitrogen-fueled trains zip from city to European city?
The engineering behind nitrogen powered cars is pretty compelling, but there are some big drawbacks to using nitrogen as a vehicle fuel source. First and foremost is that nitrogen is very heavy. Imagine the weight of carrying a load of compressed liquid nitrogen, the necessary coolant to keep is liquid, the weight of the container, and the weight of the engine itself. Sure, nitrogen does deliver more power than batteries, but the power/weight ratio would seem to be prohibitive to me. Even factoring in the composite materials that would presumably be developed in the next 50 years, nitrogen just doesn't have the performance to justify the weight.
The fuel of the future, IMHO is hydrogen. Long maligned for the Hidenburg disaster, hydrogen is a fuel source with a lot of potential. (In fact, it was *not* hydrogen that caused the Hindenburg disaster. Static electricity discharged between sections of the outer skin covering, igniting the highly flammible weatherproofing compound that covered the skin of the Hindenburg. That's why the fire was described as a bright orange - a hydrogen fire would be virtually colorless. The myth of a hydrogen accident on the Hindenburg has attached a stigma to hydrogen that is based on poor evidence.)
The way a car hydrogen engine could be made safe is through the use of advanced carbon nanotube technology. These nanotubes can trap the hydrogen molecules, making them safe to transport. The holy grail of hydrogen/nanotube research is a nanotube that can hold 65% of its own weight in hydrogen. Above that figure, hydrogen fuel cells become economically feasible. Hydrogen is a clean burning fuel that provides a great deal of energy and can power a car with greater efficiency than electric motors or gasoline engines. If someone can create a nanotube storage system (and there have been rumors that breakthroughs are pending - they're at least up to 10% hydrogen/carbon) then hydrogen will become the fuel of choice for automobiles.
The specific heat of liquid nitrogen is pretty low. So it's not that dangerous in the event of an accident, although if you were completely bathed in it, it would kinda suck. I guess it's a matter of quantity...
But back in the physics department, we used to shoot each other with liquid nitrogen from squirt guns. Yow! That gets your attention.
Then there was Frank, who would actually swallow a few drops, and belch long musical selections.
As for transporting it, a thermos dewar is your best bet. Make it out of stainless steel, so you don't have shattering glass in an accident. I'm not sure how much you'll need to have in your tank to fuel the car though, so it may get big, bulky, and heavy.
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Just so we don't get stupid arguments like "if we can get energy from the air, why can't we just make an engine that runs on air?", the thermodynamic principle here is that a heat engine can produce work from a temperature difference, by letting the energy flow from hotter to cooler while "skimming" off part of the energy to transform into work. The percentage that it skims is the complement of the efficiency, which obviously can't be higher than 100%.
So a theoretically generalized heat engine doesn't care whether you carry around a fire or a block of ice, or (for that matter) if you skim along with one ski in a trough of cold water and another ski in a trough of hot water, as long as it's got access to a temperature difference. In practice, of course, you've got to design different engines if you want reasonable efficiency.
Incidentally, being from the frosty Northern near-state of Canada, I'd really rather not have a car without a toasty hot engine. While you can use liquid nitrogen to heat your cab, it's not terribly efficient. However, people who live in hot places might appreciate the cheap, efficient, and simple air-conditioning.
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