It moves the emissions somewhere else

BBC NEWS | Science/Nature | Five-seat concept car runs on air:

An engineer has promised that within a year he will start selling a car that runs on compressed air, producing no emissions at all in town. The OneCAT will be a five-seater with a glass fibre body, weighing just 350kg and could cost just over £2,500. It will be driven by compressed air stored in carbon-fibre tanks built into the chassis. The tanks can be filled with air from a compressor in just three minutes – much quicker than a battery car.

Now moving emissions somewhere else (or eliminating them almost entirely if your power comes from solar, wind or hydro) isn’t necessarily a bad thing, but it pisses me off when people talk about no emissions from the car as if it were no emissions period. If you get your electricity for running the compressor from a dirty coal plant and send it over lossy transmission lines, you’ll be doing much worse than burning gasoline in an efficient engine and using that to drive your car.

Another thing that kinda took me aback is the amount of air they’re talking about: 90 cubic meters, about the amount of air in a typical large-ish living room. Compressed to just a touch under 300 atmospheres. A full load of “fuel” will weigh about 110 kilos, or 1/3 the projected empty weight of the car. And they expect to be able to pump the tank up in three minutes…

Oh, and one last thing, speaking of moving emissions elsewhere. The expansion process relies on outside heat to keep the air from leaving the tailpipe at cryogenic temperatures (instead it’s only at -15 C or so). So the waste heat generated by the compression process is sorta counterbalanced by the heat sucked out of the air while running the engine. Unless, of course, you try to drive somewhere that’s really cold, really damp or both…


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