Compressed air as fuel?

[Dancing Fingers]

Hi Guys,
I remember years ago Kitplanes did a series on the potential for
batterry-powered aircraft. Recently, I watCHED Future Cars on the
Discovery channel and this guy had developed a car that ran on
compressed air. This seems like a more viable fuel for aircraft then
batteries. Has anybody looked into it?
just curious.
Chris

[Bill Daniels]

I remember flying model airplanes powered by a tiny single cylinder CO2
engine. The engine had "warming" fins on the cylinder to help the CO2
expand. The "fuel supply" was a CO2 cartridge. Compared to glo-plug
2-strokes, it was heavy and expensive to run.

Compressed air makes a lot of sense for a 'city car' or taxi. Unlike
battery/electrics, a recharge takes only minutes and the exhaust is just
air. Compressed air vehicles have a long history in underground mining
where the lack of polutants is a plus. .

Would it work for a man carrying airplane? Maybe, if you didn't want much
range or payload - or to fly in cold weather. You want hot weather to make
the gas expand. The trick would be ultra high pressure tanks made of carbon
fiber and a very efficient air engine.

Bill Daniels


"Dancing Fingers" > wrote in message
oups.com...
> Hi Guys,
> I remember years ago Kitplanes did a series on the potential for
> batterry-powered aircraft. Recently, I watCHED Future Cars on the
> Discovery channel and this guy had developed a car that ran on
> compressed air. This seems like a more viable fuel for aircraft then
> batteries. Has anybody looked into it?
> just curious.
> Chris
>

[Vaughn Simon]

"Dancing Fingers" > wrote in message
oups.com...
> Hi Guys,
> I remember years ago Kitplanes did a series on the potential for
> batterry-powered aircraft. Recently, I watCHED Future Cars on the
> Discovery channel and this guy had developed a car that ran on
> compressed air. This seems like a more viable fuel for aircraft then
> batteries. Has anybody looked into it?

Air power has been looked into for commuter vehicles. There is a company
that has been promising to make something called the "Aircar" for several years
now. They always claim to be constructing a factory, have plenty of orders in
hand, and full production is always going to start "next year". Sound like
anyone we know?

The fact is that compressed air is a very thermally inefficient way to
store energy. The reasons are buried in basic, fundamental physics. The
problem is that when you compress air, it gets hot. That heat must be thrown
away. But that is not the only problem! When you go to expand the air to
produce energy, it gets cold! This reduction in temperature greatly limits
expansion and reduces an engine's output.

Making an efficient air engine is not a trivial exercise. To be efficient,
you must find some way of allowing the air to expand to many times its
compressed volume. This may be done several ways, but all of them increase the
complexity and/or the size of the engine.

Vaughn

[Harry K]

On Jun 26, 6:15 pm, "Vaughn Simon" >
wrote:
> "Dancing Fingers" > wrote in message
>
> oups.com...
>
> > Hi Guys,
> > I remember years ago Kitplanes did a series on the potential for
> > batterry-powered aircraft. Recently, I watCHED Future Cars on the
> > Discovery channel and this guy had developed a car that ran on
> > compressed air. This seems like a more viable fuel for aircraft then
> > batteries. Has anybody looked into it?
>
> Air power has been looked into for commuter vehicles. There is a company
> that has been promising to make something called the "Aircar" for several years
> now. They always claim to be constructing a factory, have plenty of orders in
> hand, and full production is always going to start "next year". Sound like
> anyone we know?
>
> The fact is that compressed air is a very thermally inefficient way to
> store energy. The reasons are buried in basic, fundamental physics. The
> problem is that when you compress air, it gets hot. That heat must be thrown
> away. But that is not the only problem! When you go to expand the air to
> produce energy, it gets cold! This reduction in temperature greatly limits
> expansion and reduces an engine's output.
>
> Making an efficient air engine is not a trivial exercise. To be efficient,
> you must find some way of allowing the air to expand to many times its
> compressed volume. This may be done several ways, but all of them increase the
> complexity and/or the size of the engine.
>
> Vaughn

The heat/cool bit is the big drawback. That heat being thrown away on
both ends is not free. The air vehicles seen in service are always in
special use applications, all are short haul type and all rely on a
HUGE store of precompressed air to retank from. In general, the cost
of the air, due to the heat loss alone, makes it a very expensive way
to fuel an engine.

Harry K

[Orval Fairbairn]

In article . com>,
Dancing Fingers > wrote:

> Hi Guys,
> I remember years ago Kitplanes did a series on the potential for
> batterry-powered aircraft. Recently, I watCHED Future Cars on the
> Discovery channel and this guy had developed a car that ran on
> compressed air. This seems like a more viable fuel for aircraft then
> batteries. Has anybody looked into it?
> just curious.
> Chris

You ned either:
1. a very long hose attached to a compressor or

2. a filament-wound balonium/unobtanium air tank filled with air
compressed to 100,000,000 psi.

Otherwise, you just can't carry enough compressed air around to make a
practical vehicle.

The "Future Car" ranks right there along with Moller's "Skycar," in that
it is all vaporware.

[Dancing Fingers]

On Jun 26, 10:23 pm, Orval Fairbairn >
wrote:
> In article . com>,
> Dancing Fingers > wrote:
>
> > Hi Guys,
> > I remember years ago Kitplanes did a series on the potential for
> > batterry-powered aircraft. Recently, I watCHED Future Cars on the
> > Discovery channel and this guy had developed a car that ran on
> > compressed air. This seems like a more viable fuel for aircraft then
> > batteries. Has anybody looked into it?
> > just curious.
> > Chris
>
> You ned either:
> 1. a very long hose attached to a compressor or
>
> 2. a filament-wound balonium/unobtanium air tank filled with air
> compressed to 100,000,000 psi.
>
> Otherwise, you just can't carry enough compressed air around to make a
> practical vehicle.
>
> The "Future Car" ranks right there along with Moller's "Skycar," in that
> it is all vaporware.

I certainly don't think that compressed air would power a airliner but
it might be viable for small commutter flights. It seems like the
heat issue would only be an issue on the ground, during refueling,
although cabin heat would be a challenge. I was really wondering if
anyone had ever calculated the energy per cubic foot compressed air
can hold, relative to gasoline, diesel and hydrogen. There's a new
engine being developed, the Quasiturbine, that would be perfect for
this application.
For what it's worth.
Chris

[cavelamb himself]

Dancing Fingers wrote:


>
> I certainly don't think that compressed air would power a airliner but
> it might be viable for small commutter flights. It seems like the
> heat issue would only be an issue on the ground, during refueling,
> although cabin heat would be a challenge. I was really wondering if
> anyone had ever calculated the energy per cubic foot compressed air
> can hold, relative to gasoline, diesel and hydrogen. There's a new
> engine being developed, the Quasiturbine, that would be perfect for
> this application.
> For what it's worth.
> Chris
>

The straight answer?

Not on this, or any other planet in this solar system...

Richard

[Vaughn Simon]

"Dancing Fingers" > wrote in message
oups.com...
> On Jun 26, 10:23 pm, Orval Fairbairn >
> wrote:
>> In article . com>,
>> Dancing Fingers > wrote:
>>
>> > Hi Guys,
>> > I remember years ago Kitplanes did a series on the potential for
>> > batterry-powered aircraft. Recently, I watCHED Future Cars on the
>> > Discovery channel and this guy had developed a car that ran on
>> > compressed air. This seems like a more viable fuel for aircraft then
>> > batteries. Has anybody looked into it?
>> > just curious.
>> > Chris
>>
>> You ned either:
>> 1. a very long hose attached to a compressor or
>>
>> 2. a filament-wound balonium/unobtanium air tank filled with air
>> compressed to 100,000,000 psi.
>>
>> Otherwise, you just can't carry enough compressed air around to make a
>> practical vehicle.
>>
>> The "Future Car" ranks right there along with Moller's "Skycar," in that
>> it is all vaporware.
>
> I certainly don't think that compressed air would power a airliner but
> it might be viable for small commutter flights. It seems like the
> heat issue would only be an issue on the ground, during refueling,
> although cabin heat would be a challenge. I was really wondering if
> anyone had ever calculated the energy per cubic foot compressed air
> can hold, relative to gasoline, diesel and hydrogen.

Kindly compare energy densities for yourself.

Jet fuel >>>>>>>> 11,694 Wh/kg
Gasoline>>>>>>>> 12,200 Wh/kg
Compressed air >> 34 Wh/kg

For a given weight of fuel, your air-powered "commutter" aircraft would have to
somehow get by with less than 1% of the range that it would have with
conventional fuel.
Source: http://xtronics.com/reference/energy_density.htm

Of course, that is gravimetric density and you asked about volumetric density.
Volumetric density would probably be an even worse comparison, but would depend
greatly on the air storage pressure you wish to assume. Naturally, you must
design your "fuel tank" heavier and heavier as storage pressure increases.
Exotic materials would help, but not enough. Also, high pressure air tanks must
be round, but the space available to contain the tank will not be round, so much
potential storage capacity would be lost.

>There's a new engine being developed, the Quasiturbine, that would be perfect
>for
>this application.

The type of engine would not matter. You just can't carry enough stored energy
to be practical.

> For what it's worth.

It is worth nothing

Vaughn

[[email protected]]

On Jun 26, 7:15 pm, "Vaughn Simon" >
wrote:
> "Dancing Fingers" > wrote in message
>
> oups.com...
>
> > Hi Guys,
> > I remember years ago Kitplanes did a series on the potential for
> > batterry-powered aircraft. Recently, I watCHED Future Cars on the
> > Discovery channel and this guy had developed a car that ran on
> > compressed air. This seems like a more viable fuel for aircraft then
> > batteries. Has anybody looked into it?
>
> Air power has been looked into for commuter vehicles. There is a company
> that has been promising to make something called the "Aircar" for several years
> now. They always claim to be constructing a factory, have plenty of orders in
> hand, and full production is always going to start "next year". Sound like
> anyone we know?
>
> The fact is that compressed air is a very thermally inefficient way to
> store energy. The reasons are buried in basic, fundamental physics. The
> problem is that when you compress air, it gets hot. That heat must be thrown
> away. But that is not the only problem! When you go to expand the air to
> produce energy, it gets cold! This reduction in temperature greatly limits
> expansion and reduces an engine's output.
>
> Making an efficient air engine is not a trivial exercise. To be efficient,
> you must find some way of allowing the air to expand to many times its
> compressed volume. This may be done several ways, but all of them increase the
> complexity and/or the size of the engine.
>
> Vaughn

Yes, but just think of all the ice cream you could make as you ran
your engine!!

[Harry K]

On Jul 12, 9:23 am, Dancing Fingers > wrote:
> On Jun 26, 10:23 pm, Orval Fairbairn >
> wrote:
>
>
>
>
>
> > In article . com>,
> > Dancing Fingers > wrote:
>
> > > Hi Guys,
> > > I remember years ago Kitplanes did a series on the potential for
> > > batterry-powered aircraft. Recently, I watCHED Future Cars on the
> > > Discovery channel and this guy had developed a car that ran on
> > > compressed air. This seems like a more viable fuel for aircraft then
> > > batteries. Has anybody looked into it?
> > > just curious.
> > > Chris
>
> > You ned either:
> > 1. a very long hose attached to a compressor or
>
> > 2. a filament-wound balonium/unobtanium air tank filled with air
> > compressed to 100,000,000 psi.
>
> > Otherwise, you just can't carry enough compressed air around to make a
> > practical vehicle.
>
> > The "Future Car" ranks right there along with Moller's "Skycar," in that
> > it is all vaporware.
>
> I certainly don't think that compressed air would power a airliner but
> it might be viable for small commutter flights. It seems like the
> heat issue would only be an issue on the ground, during refueling,
> although cabin heat would be a challenge. I was really wondering if
> anyone had ever calculated the energy per cubic foot compressed air
> can hold, relative to gasoline, diesel and hydrogen. There's a new
> engine being developed, the Quasiturbine, that would be perfect for
> this application.
> For what it's worth.
> Chris- Hide quoted text -
>
> - Show quoted text -

You can put the "quasiturbine" right in the same category as the 'air
car" and "Moller's flying car" all of them are vapor ware. To
address the 'quasitubine' specifically, It has been "under
developement for at least 10 years and I think longer with no
progress. It is an extremely complicated design for a rotary engine
with little or no improvement over the original Mazda (IIRC) rotary
engine.

The heat problem is not in getting rid of it. The problem is that
that heat was produced while compressing the air and is then thrown
away. Right there should be a clue as one of the major reasons why
and "air engine" is not an economicaly viable design. That heat costs
money and represents energy that cannot be recovered.

Harry K

[Harry K]

On Jun 26, 7:23 pm, Orval Fairbairn > wrote:
> In article . com>,
> Dancing Fingers > wrote:
>
> > Hi Guys,
> > I remember years ago Kitplanes did a series on the potential for
> > batterry-powered aircraft. Recently, I watCHED Future Cars on the
> > Discovery channel and this guy had developed a car that ran on
> > compressed air. This seems like a more viable fuel for aircraft then
> > batteries. Has anybody looked into it?
> > just curious.
> > Chris
>
> You ned either:
> 1. a very long hose attached to a compressor or
>
> 2. a filament-wound balonium/unobtanium air tank filled with air
> compressed to 100,000,000 psi.
>
> Otherwise, you just can't carry enough compressed air around to make a
> practical vehicle.
>
> The "Future Car" ranks right there along with Moller's "Skycar," in that
> it is all vaporware.

Ah yes the "Skycar" Seems he has given up trying to scam people with
that. He is now touting it as a Ground Effect vehicle and still
showing it in operation on the tether only. A long thread is
currently running in rec.aviation.homebuilt.

Harry K

[Harry K]

On Jul 12, 7:48 pm, Harry K > wrote:
> On Jun 26, 7:23 pm, Orval Fairbairn > wrote:
>
>
>
>
>
> > In article . com>,
> > Dancing Fingers > wrote:
>
> > > Hi Guys,
> > > I remember years ago Kitplanes did a series on the potential for
> > > batterry-powered aircraft. Recently, I watCHED Future Cars on the
> > > Discovery channel and this guy had developed a car that ran on
> > > compressed air. This seems like a more viable fuel for aircraft then
> > > batteries. Has anybody looked into it?
> > > just curious.
> > > Chris
>
> > You ned either:
> > 1. a very long hose attached to a compressor or
>
> > 2. a filament-wound balonium/unobtanium air tank filled with air
> > compressed to 100,000,000 psi.
>
> > Otherwise, you just can't carry enough compressed air around to make a
> > practical vehicle.
>
> > The "Future Car" ranks right there along with Moller's "Skycar," in that
> > it is all vaporware.
>
> Ah yes the "Skycar" Seems he has given up trying to scam people with
> that. He is now touting it as a Ground Effect vehicle and still
> showing it in operation on the tether only. A long thread is
> currently running in rec.aviation.homebuilt.
>
> Harry K- Hide quoted text -
>
> - Show quoted text -

Ooops. I thought I was still over in alt.home.repair

Harry K

[Vaughn Simon]

"Harry K" > wrote in message
s.com...
> The heat problem is not in getting rid of it. The problem is that
> that heat was produced while compressing the air and is then thrown
> away. Right there should be a clue as one of the major reasons why
> and "air engine" is not an economicaly viable design. That heat costs
> money and represents energy that cannot be recovered.

This was already explained to the OP, and seems to have made no impression.

Vaughn

[Ernest Christley]

Dancing Fingers wrote:

> I certainly don't think that compressed air would power a airliner but
> it might be viable for small commutter flights. It seems like the
> heat issue would only be an issue on the ground, during refueling,
> although cabin heat would be a challenge. I was really wondering if
> anyone had ever calculated the energy per cubic foot compressed air
> can hold, relative to gasoline, diesel and hydrogen. There's a new
> engine being developed, the Quasiturbine, that would be perfect for
> this application.
> For what it's worth.
> Chris
>

Not only is the energy density of the compressed air ridiculously low
and nearly impossible to utilize efficiently, but nearly all of the
alternative energy schemes require that the entire set of propellant be
carried. With traditional fuels, the oxidizer is collected as it is
used. Between 12 and 17 pounds of air is ingested for each pound of
fuel carried.

[Dan[_2_]]

Harry K wrote:
<snip>

It is an extremely complicated design for a rotary engine
> with little or no improvement over the original Mazda (IIRC) rotary
> engine.

Wankel?

Dan, U.S. Air Force, retired

[Roger (K8RI)]

On Tue, 26 Jun 2007 14:28:14 -0700, Dancing Fingers
> wrote:

>Hi Guys,
>I remember years ago Kitplanes did a series on the potential for
>batterry-powered aircraft. Recently, I watCHED Future Cars on the
>Discovery channel and this guy had developed a car that ran on
>compressed air. This seems like a more viable fuel for aircraft then
>batteries. Has anybody looked into it?

No matter how you describe it compressed air is not a fuel although it
can be used as a source of stored energy which is quite different. The
amount of energy you could store in compressed air is a tiny fraction
of what you can get from conventional, or even bio fuels. I doubt you
could build a 4 passenger plane capable of making it around the
pattern on compressed air let alone any thing larger. It takes a lot
of energy to compress the air and then you only get a portion of that
back. It's probably one of the most inefficient and energy hungry
systems tried.

Battery technology is making some tremendous strides in current
density, but they are heavy, dangerous, (The higher the current
density the more dangerous) and a problem when it comes time to
dispose of them. Even at their best they have only worked on very
light experimental aircraft and although they carry much more energy
than compressed air is capable of doing, they are still far inferior
to conventional fuel.


>just curious.
>Chris