Compressed Air powered, zero emission cars - for $6.5K each

On 4 Oct 2006 06:32:41 -0700, "BobG" > wrote:

>This site has a table of energy density by weight and volume and
>compressed air is worse than batteries. (Hint... most air compressors
>I've seen are big noisy 220V several HP contraptions and they huff and
>puff and finally shut off at a whopping 150 psi.)
>http://xtronics.com/reference/energy_density.htm

Energy density by weight is not an issue except
for big hills, one of the reasons for using air is to have
regenerative braking, and with regenerative braking,
weight is not anywhere near as critical, if at all.

And storage is apparently not at 150 psi,
it is hundreds of bars, which is 3000 psi or more.
While storage tanks are high tech for this
pressure range, it makes a big difference in
whether or not the vehicle has any utility.

If regenerative braking were perfect (100
percent efficient), the energy needed to make
a trip would only be the bearing friction (which
should be negligible for good bearings), rolling
friction (which can be reduced by less flex in
the tires), and air resistance (which should also
be negligible at low speeds and no wind).

It is these facts that make EVs or any
other technology that supports good regenerative
braking viable at all.

The auto industry has not placed good
physics above inept road testing programs, and
they need to start from scratch, with good physics,
and build cars that take almost no energy at all
to make a trip on level ground!
Only then will the myth of weight being
a critical issue be discarded and the understanding
that it has been hills and overpowered ICE engines
that have been wasting all the energy (plus having
an engine running and wasting energy waiting at
traffic lights).

Joe Fischer

BobG wrote:
> This site has a table of energy density by weight and volume and
> compressed air is worse than batteries. (Hint... most air compressors
> I've seen are big noisy 220V several HP contraptions and they huff and
> puff and finally shut off at a whopping 150 psi.)
> http://xtronics.com/reference/energy_density.htm

Your ref:
Compressed Air (no pressure indicated) 17 Wh/l 34 Wh/kg

http://en.wikipedia.org/wiki/Energy_density
"compressed air at 20 bar" 0.27MJ/kg

1MJ/Kg is roughly 278Wh/kg
1 bar is about 14.5psi

Thus the limit appears to be 75Wh/kg at 290psi (about 3 times that of a
lead/acid battery)

However:
http://www.futurepundit.com/archives/000129.html
"the air is both cooled to minus 100 degrees Centigrade and compressed
to 4,500 pounds per square inch"

http://www.activepower.com/files/whi...WhitePaper.pdf
"TACAS begins with compressed air stored in conventional gas cylinders
or pressure vessels. In order to meet the system's performance
targets, it is necessary to store compressed air at high pressures,
ideally 4500 pounds per square inch (PSI) or more. These pressures are
routine for Self-Contained Breathing Apparatus (SCBA) compressors and
fill stations used by fire departments and diving operations. Gas
cylinders rated up to 6000 PSI are widely available."

This is one of the resulting products - an 85kW (for 15 minutes) DC UPS
supply
http://www.activepower.com/files/pro...ec_CoolAir.pdf

A car needs to be able to run for 300+ miles at 60mph using the power
equivalent demand of 30-50kW, a total energy storage/delivery of about
200kWh. Thus a unit only 10 times more efficient could power a car.

I realise that the UPS shown is 1270kg on its own, but it has redundant
extras to maintain storage and produce millisecond response times that
a car storage/power unit would not need. The proposed system could
easily be designed to weigh less than an engine and fuel tank combined.

So try not to write the system off with so little understanding of the
facts.

Joe Fischer wrote:
> It is these facts that make EVs or any
> other technology that supports good regenerative
> braking viable at all.

Aha - yes - I was wondering where the 10 times efficiency savings would
come from. Regenerative braking (built in to those UPS units, in
effect) would bring the total storage needs down considerably.

Hoggle wrote:
> BobG wrote:
> > This site has a table of energy density by weight and volume and
> > compressed air is worse than batteries. (Hint... most air compressors
> > I've seen are big noisy 220V several HP contraptions and they huff and
> > puff and finally shut off at a whopping 150 psi.)
> > http://xtronics.com/reference/energy_density.htm
>
> Your ref:
> Compressed Air (no pressure indicated) 17 Wh/l 34 Wh/kg
>
> http://en.wikipedia.org/wiki/Energy_density
> "compressed air at 20 bar" 0.27MJ/kg
>
> 1MJ/Kg is roughly 278Wh/kg
> 1 bar is about 14.5psi
>
> Thus the limit appears to be 75Wh/kg at 290psi (about 3 times that of a
> lead/acid battery)
>
> However:
> http://www.futurepundit.com/archives/000129.html
> "the air is both cooled to minus 100 degrees Centigrade and compressed
> to 4,500 pounds per square inch"
>
> http://www.activepower.com/files/whi...WhitePaper.pdf
> "TACAS begins with compressed air stored in conventional gas cylinders
> or pressure vessels. In order to meet the system's performance
> targets, it is necessary to store compressed air at high pressures,
> ideally 4500 pounds per square inch (PSI) or more. These pressures are
> routine for Self-Contained Breathing Apparatus (SCBA) compressors and
> fill stations used by fire departments and diving operations. Gas
> cylinders rated up to 6000 PSI are widely available."
>
> This is one of the resulting products - an 85kW (for 15 minutes) DC UPS
> supply
> http://www.activepower.com/files/pro...ec_CoolAir.pdf
>
> A car needs to be able to run for 300+ miles at 60mph using the power
> equivalent demand of 30-50kW, a total energy storage/delivery of about
> 200kWh. Thus a unit only 10 times more efficient could power a car.
>
> I realise that the UPS shown is 1270kg on its own, but it has redundant
> extras to maintain storage and produce millisecond response times that
> a car storage/power unit would not need. The proposed system could
> easily be designed to weigh less than an engine and fuel tank combined.
>
> So try not to write the system off with so little understanding of the
> facts.

I got lost trying to read through all of your links, so I'll give it a
try later with a cup of coffee.

But the one indicating they are both cooling the air to minus 100
degrees and compressing it to 4,500 psi indicates a lot of energy is
being transferred to come up with a supply of air that is packed
tightly enough to provide sufficient expansive power to propel a car.
That transferred energy comes at a financial and environmental cost
which appears to be ignored. If they are able to store compressed air
at those pressures and temperatures do you know how large and heavy
would the storage tank(s) have to be to give the car a range of 200
miles.

Dave Gower wrote:

> "Anthony Matonak" > wrote
>
>
>>... the idea isn't any worse than electric or hydrogen cars.
>>The energy for all these technologies have to come from somewhere else.
>
>
> Yes it is worse, much worse. The overall efficiency is far lower, for a
> variety of reasons, chief of which is the pathetic energy density which
> forces the vehicle to waste a huge percentage of its limited energy carrying
> heavy air tanks.

The biggest drawback to using compressed air as an energy storage method
is that just the STORAGE process, nevermind utilization, cannot possibly
be more than 50% efficient unless you perfectly insulate the air
delivery lines and the air storage tank so that the air doesn't ever
cool down from the time it leaves the compressor until it is used for power.

When you compress a gas, you heat the gas. The heat is normally removed
by cooling the gas before it gets to the air storage tank, because if
you put it in the tank hot the pressure in the tank will drop as the gas
cools. But either way, a minimum of 50% of the energy delivered by the
air compressor gets dumped away as heat from the compression process.

Compressed air power makes lots of sense for air tools, pneumatic lifts,
dental drills, and other applications where efficiency is far less
important than durability, lack of an ignition source, self-cooling
motors, etc. But its DUMB DUMB DUMB for something like a vehicle!

On 4 Oct 2006 "John S." > wrote:

>But the one indicating they are both cooling the air to minus 100
>degrees and compressing it to 4,500 psi indicates a lot of energy is
>being transferred to come up with a supply of air that is packed
>tightly enough to provide sufficient expansive power to propel a car.

Cooling the air may be part of another process,
maybe the heat extracted is used for something.

But compressing the air is NOT a waste of energy,
it IS the energy that will move the vehicle. :-)

The argument of compressing combustible fuels
being a waste of energy is valid, but compressing in and
of itself is not what causes the waste, it is not using the
compression for anything after that which is wasteful.

>That transferred energy comes at a financial and environmental cost
>which appears to be ignored. If they are able to store compressed air
>at those pressures and temperatures do you know how large and heavy
>would the storage tank(s) have to be to give the car a range of 200
>miles.

There are no ICE vehicles to compare this against,
because air may be one of about four possible viable
regenerative braking systems.

I doubt if 200 mile range is offered or needed,
I drove a cab in 1950, 12 hours or more per day, and
rarely went 200 miles.
Air tanks could be exchanged, although they
may be heavy, but possibly not even as heavy as
a liquid propane tank if the air is not liquified.

The idea may be oversold, or suspicious,
after all it came from France :-), but for certain
uses it may be an extremely useful technology.

The motors look identical to hydraulic
motors being used on aircraft in 1946 when I
was an A & E mechanic instructor, so I have
an open mind as to how much range a tank
of air will hold.

Without the possibility of regenerative
braking, the idea would be rather dumb.
Contests should be held where the
least amount of energy would be used over
a closed course with traffic lights, stop lights,
and some straight-aways, because regenerative
braking is the key to range in city driving.

Joe Fischer

On Wed, Steve > wrote:

>Compressed air power makes lots of sense for air tools, pneumatic lifts,
>dental drills, and other applications where efficiency is far less
>important than durability, lack of an ignition source, self-cooling
>motors, etc. But its DUMB DUMB DUMB for something like a vehicle!

Not when compared to a 15 percent polluting
ICE vehicle in city traffic.

What else could possible be less than 15 percent
efficient?

Joe Fischer

Joe Fischer wrote:

> On Wed, Steve > wrote:
>
>
>>Compressed air power makes lots of sense for air tools, pneumatic lifts,
>>dental drills, and other applications where efficiency is far less
>>important than durability, lack of an ignition source, self-cooling
>>motors, etc. But its DUMB DUMB DUMB for something like a vehicle!
>
>
> Not when compared to a 15 percent polluting
> ICE vehicle in city traffic.

YES when compared to that, because the 50% waste of compressing air
doesn't include:

1) the frictional losses of the compressor
2) the losses of the compressor motor
3) the transmission losses from the power plant to the compressor
4) the inefficiency of the power plant

and on the utilization end:

1) the flow losses in the air plumbing
2) the inefficiency (gross, by the way!) of the air-powered motors

I'd say when you total it up you'd be lucky to get the overall
efficiency of a compressed-air powered vehicle above 1%. 15% starts
looking DAMN good!
>
> What else could possible be less than 15 percent
> efficient?

Compressed air power, for one.

On Wed,Steve > wrote:

>Joe Fischer wrote:
>> Not when compared to a 15 percent polluting
>> ICE vehicle in city traffic.
>
>YES when compared to that, because the 50% waste of compressing air

Why do you say compressing the air is a waste?

>doesn't include:
>
>1) the frictional losses of the compressor
>2) the losses of the compressor motor
>3) the transmission losses from the power plant to the compressor
>4) the inefficiency of the power plant
>
>and on the utilization end:
>
>1) the flow losses in the air plumbing
>2) the inefficiency (gross, by the way!) of the air-powered motors
>
>I'd say when you total it up you'd be lucky to get the overall
>efficiency of a compressed-air powered vehicle above 1%. 15% starts
>looking DAMN good!

If it was anything close to one percent, even the
French would not be touting it.

Also, note that most of French electricity comes
from nuclear, possibly allowing some discussion about
the cost.

In many cities, any reduction in pollution is
a plus, and for Americans, the price Europeans pay
for petrol is absurd, so surely that is a factor.

>> What else could possible be less than 15 percent
>> efficient?
>
>Compressed air power, for one.

I hardly think so, on the end use, it should be
around 50 percent, compared to a good electric
system of 80 percent.

Friction and the cooling may be the only
real waste in compressing air, so with hydro or
nuclear, in a big city that may have stagnant air,
and gasoline costing over a dollar per litre, what
could possibly be wrong with it.

I am assuming it gives very good regenerative
braking, which is required to make the system work.

Joe Fischer

John S. wrote:
> I got lost trying to read through all of your links, so I'll give it a
> try later with a cup of coffee.

I apologise for using referenced evidence in my arguments. I realise I
am virtually unique in this regard on usenet.

http://www.theaircar.com/
This website will answer many of your questions (although it is badly
out of date and many of the links have not been changed to stay on the
English site, so being able to read spanish will help).