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#11
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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 |
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#12
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Compressed Air powered, zero emission cars - for $6.5K each
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. |
#13
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Compressed Air powered, zero emission cars - for $6.5K each
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. |
#14
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Compressed Air powered, zero emission cars - for $6.5K each
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. |
#15
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Compressed Air powered, zero emission cars - for $6.5K each
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! |
#16
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Compressed Air powered, zero emission cars - for $6.5K each
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 |
#17
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Compressed Air powered, zero emission cars - for $6.5K each
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 |
#18
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Compressed Air powered, zero emission cars - for $6.5K each
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. |
#19
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Compressed Air powered, zero emission cars - for $6.5K each
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 |
#20
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Compressed Air powered, zero emission cars - for $6.5K each
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). |
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