Re: Guy Negre's compressed air cars

From: Doug Jones (
Date: Sat Mar 10 2001 - 19:17:04 MST

scerir wrote:
> Name = Eolo
> Price = less then $10,000
> Speed = 110 km/h
> Range = about 200 km
> Power = circa 25 hp
> At the end of _this_ month
> about 10 of these cars will be
> running in the Vatican City.

Hmmmm... the trick of using a 20 bar compressor as a heat source is
kinda slick- it produces just enough hot air at the right pressure to
allow mixing rather than a heat exchanger to warm up the air from the
high pressure storage bottles. The end-to-end efficiency of this system
is inherently poor though, since compressing the air to 300 bars
typically requires a four- or five- stage compressor with intercoolers,
which typically throw away more than 80% of the input shaft power as
heat. (I've been working on cobbling together a 6000 psi compressor for
helium from a 3000 psi scuba bottle compressor and a haskel pump, so
I've learned a lot about this area.)

The total energy storage of a volume of gas can be no greater than PV,
so the figures for mileage and power output are probably a total crock-
a liter of air at 300 bars stores only 30,000 joules of energy, about
1/1000 the heat energy in a liter of gasoline. To achieve 50 hp-hours
as claimed above (call it 130 MJ), one would need about 4.5 m3 of 300
bar gas storage- about a 2 meter sphere.

Even if the power listed is peak and not cruise, .5 m3 of 300 bar
storage is a lot... and having tens of megajoules of compressed gas
under your butt in a traffic accident could be exciting, to put it

Doug Jones, Rocket Engineer
XCOR Aerospace

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