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Old 12-31-2008, 08:13 PM   #7 (permalink)
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Originally Posted by Big Dave View Post
Compressed air vehicles are used where fire safety is at a premium. The US Navy operates a compressed-air locomotive at its ammunition storage depot at Pearl Harbor.
Compressed air locomotives were also popular in mines in the early 1900's. HK Porter was the leading manufacturer. Typically they were 3 or more stages, with reheaters between stages.

Compressing air generates a lot of heat. In mines, they would use that heat to heat up water, then load that hot water onto the locomotive. The hot water would then be used to reheat the air between the stages of the air motor.

All of this was to make the whole cycle run closer to the more efficient isothermal cycle rather than the very inefficient adiabatic cycle.

MDI's Guy Negre has developed a cute technique of compressing some ambient air (which heats it) and then mixing it with a burst of air from the high pressure tank to drive the piston back down. This appears to be another way to get the engine efficiency up by making it run closer to isothermal.

But the low energy density of compressed air is still the big problem. At best, compressed air is about equal to that of old technology lead-acid batteries in watt-hours per liter or watt-hours per kilogram.

The real competition for the Airpod are the many neighborhood electric vehicles (NEVs) that are being announced. They are what you get by taking golf carts and making them look pretty.
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