Air cars


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Posted by Sherman in Idaho [24.32.202.166] on Monday, January 28, 2013 at 20:53:51 :

In Reply to: 117 mpg----ot posted by clueless [201.202.29.210] on Monday, January 28, 2013 at 18:34:23 :

It seems like every decade or so, someone (usually a college professor) "invents" an air-powered car. They can never succeed because the laws of thermodynamics are stacked against them, but reporters always love to cover the story anyway.

The first problem, of course, is that some conventional source of energy has to be used to compress the air, and "electricity" is not a source.

The second problem is that when you compress air, it gets hot. That heat represents energy you bought in order to compress the air, but the heat all dissipate into uselessness by the time you're ready to use what energy is stored in the compressed air. So, before the air even comes out of the tank, you're already "in debt" energy-wise by the amount of heat that left the air between the compressor cylinder and your car. But that's not the end of it. When you go to expand the compressed air in your engine, it gets cold. Or looking at it another way, you have to suck heat out of the atmosphere to warm it up. To the extent that you're not able to warm the exhaust sufficiently, you're wasting even more of the energy stored in that compressed air.

The bottom line is air-"powered" vehicles are insanely inefficient. Add to that the inefficiency of generating electricity, transmitting it, and running the air compressor and there's no way it can every possibly be competitive with any sort of internal combustion engine.

Compressed air motors aren't even anything new. They've been used for nearly 100 years in little locomotives called "motors" used to pull ore cars underground in mines. The mine motors carry a compressed air tank of maybe 50-100 cubic feet, and can be refilled from lots of places in the mine, since mines have compressed air run all over to power the rock drills, slushers, and mucking machines. They even have air-powered chain saws underground. The advantage over electric and diesel in that sort of application is that there are no dangerous gasses or fumes to deal with and no chance of starting a fire. Efficiency is barely even a consideration.



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