French Air-powered Car To Trials

[vanvaley1]

Re: French Air-powered Car To Trials

I like the idea of an air-powered car. Too bad if they rush it into production before it's ready and can prove itself worthy for public consumption. As for me, having been hit three times by other vehicles...once using the jaws of life to get me out...and the other fellows being sited and raising two kids through the teenage werewolve driving stage, I'm high on safety issues. Get the the darn thing to withstand an 18 wheeler or angry golf cart impact and I'll buy one.

[metalman]

Re: French Air-powered Car To Trials

I like the idea of an air-powered car. Too bad if they rush it into production before it's ready and can prove itself worthy for public consumption. As for me, having been hit three times by other vehicles...once using the jaws of life to get me out...and the other fellows being sited and raising two kids through the teenage werewolve driving stage, I'm high on safety issues. Get the the darn thing to withstand an 18 wheeler or angry golf cart impact and I'll buy one.

oh, did i forget to mention that the only possible way to get one to 55mph is if it weighs less than 800 lbs? hit it with an ave. car 3240 lbs and think cue ball hitting a golf ball... you the passenger gets to absorb part of the difference. that's after you either ran out of air or froze your ass off.

[Verrocchio]

Re: French Air-powered Car To Trials

Air power doesn't have to demonstrate an advantage over gasoline power. It merely has to solve the battery problem. Wind and solar are limited in their utility without a solution to this problem. What is the cheapest and durable means of storing energy (from the electric grid) in a usable form that will power the vehicle to the job, shop, or market and back to the recharging site?

[Munger]

Re: French Air-powered Car To Trials

The stored energy of compressed air is very low -- but that is not where the energy to power the car is coming from

Read this discussion at the Oil Drum -- maybe then you will understand

Compressed Air Energy Storage - How viable is it?

Quote:

So what about compressed air? Surely a cylinder of compressed air contains energy that could be used to drive something? This is where it all becomes a little strange. The energy content of compressed gas isn't very different from that of uncompressed gas (this is the number that you are bandying about!) at the same temperature. For an ideal gas, the energy contents are identical. How come we can get work from the compressed gas? The answer is that compressed gas has a lower entropy than the uncompressed gas, and that the amount of useful work you can get out of something when it changes depends both on the change in energy content and the change in entropy. We usually focus so much on the energy side of things that we ignore the entropy side. . . . .

Metalman, I know you have a short attention span ;) -- But please do read this and understand it if you want to take a meaningful part in this discussion -- if you do not understand the facts, keep your nose out of it! ;)

Actually, I was talking indeed about the entropy of the system (or rather, the lack of entropy). The energy is in the pressure differential - not the gas itself.

Entropy is order. Things that have order tend to go to disorder (the 2nd law of thermodynamics).

An example: a teacup when dropped will break into many pieces. But the reverse does not happen - we do not see pieces of teacups spontaneously forming into a whole teacup. Why is this? Because of entropy. What does this mean? Essentially, there are a whole lot more combinations of ways of arranging the teacup particles when broken than when whole.

That is entropy. More possible states. When you jam something into a less probable state, it does not want to stay there.

Put simply - there is one way to arrange the particles to make the teacup. But there are bajillions of ways to make a broken teacup. Why do things tend to disorder? Because the universe is expanding.

Now - what does this have to do with our compressed gas? Well, when you compress a gas into a container think about what you are doing: you are taking air particles from the surrounding atmosphere and jamming more air particles in the container than want to be there (specifically, more air particles than would occupy the volume by force of sheer chance).

You are concentrating air particles in the container space.

To make this concrete, lets think about this in a closed system. Let's say you are in a sealed gymnasium. There are 100 air particles in the gymnasium. Let's say you pack 80 of these particles into a beer bottle. There are 20 left in the gymnasium. Now open the lid on the beer bottle and answer me this question: are there more ways the 80 particles can be arranged within the beer bottle or more ways they can be arranged outside of the beer bottle?

The energy is not in the air particles themselves. It is in the pressure differential. Or, put another way, in the (lack of) entropy in the system. Which is also the number you get by 2.5 * natural_log(pressure_after/pressure_before).

[Rajiv]

Re: French Air-powered Car To Trials

You can look at te MDI Bench Tests for yourself -- Energy audit carried out by the department of energetics of l’Ecole des Mines of Paris (July 2003)

[Munger]

Re: French Air-powered Car To Trials

You can look at te MDI Bench Tests for yourself -- Energy audit carried out by the department of energetics of l’Ecole des Mines of Paris (July 2003)

I don't know about the department or whether they are on the up and up. I am just noting that the energy capable of being stored by air is 100 times less than that stored by gasoline. If your car weighs 1/100th as much then you will go just as far ;)

[Rajiv]

Re: French Air-powered Car To Trials

Again the MDI stores 90 cu m of air at 300 bar which is 300 litres of compressed air which will result in roughly 26kwh of energy "stored" -- I believe that the utilization rate is 81% delivered to the wheels -- so we have a 10x tank size, and a 6x improvement in energy utilization and roughly 1/3 the range of a gasoline engine

The numbers do add up

So there is a place for the compressed air transport, particularly in an urban setting -- of course it does not have the versatility of the current gasoline powered vehicles.

The MDI engine is not the most efficient and there are more efficient versions available e.g. Engineair’s Ultra-Efficient Rotary Compressed-Air Motor

In Melbourne, Australia, an Italian-born mechanical engineer named Angelo Di Pietro has been experimenting for many years to find a more efficient design than the traditional reciprocating combustion engine. Inspired by his earlier work on Wankel rotary engines at Mercedes Benz in Germany, he pursued the notion of a rotary engine with fewer parts. Since his 1999 breakthrough, Di Pietro has been testing and perfecting his unique design which also eliminates traditional pistons and their housings. Though it weighs only 13 kilograms (28.6 lb), this rotary air motor is capable of powering a car without creating any pollution.

it converts virtually all the energy fed to its motors into actual motion. With the elegance of absolute simplicity
.
.
.
.

By comparison, the traditional car’s engine uses up to about 65% of the energy potentially available from the fuel, just to move all its parts such as pistons and cams, plus what is wasted generating excess heat. Then the transmission uses 6%, the accessory load 2% and idling losses come to about 11%, leaving about 16% of the energy actually engaged in making the wheels turn. Because of the weight of all these structures, the engine block, crankshaft, gears, transmission, etc., that 16% of the energy is having to move a vehicle weighing perhaps a ton and a half – which may have only one person sitting in it, weighing only 150 lb.

[Guest]

Re: French Air-powered Car To Trials

CharlesTMungerFan -

I am absolutely a rank layman on the topic you are discussing, but I think you blew off Rajiv's recommendation that you read that report and digest it. Your dismissal seemed a little casual to this reader. Leaves me concluding that Rajiv's argument is being a mite more scrupulous.

Respectfully.

I don't know about the department or whether they are on the up and up. I am just noting that the energy capable of being stored by air is 100 times less than that stored by gasoline. If your car weighs 1/100th as much then you will go just as far ;)

Originally Posted by Rajiv
You can look at the MDI Bench Tests for yourself -- Energy audit carried out by the department of energetics of l’Ecole des Mines of Paris (July 2003)

[petertribo]

Re: French Air-powered Car To Trials

MDI is not just talking about PROPULSION, they are also considering other factors:

"In 1999, MDI imagined and created the “Dealer/Manufacturer/Partner” concept by commercializing turnkey factories to manufacture cars locally. Unlike the huge classic assembly plants (particularly pollutant), the MDI concept offers various micro production factories throughout the world.
These plants will manufacture 80% of the vehicle and will sell them in the same location.

This concept represents a drastic decrease in costs and the logistic problems associated with the conventional process (stocks and freight of finished cars to the dealers etc...) and not withstanding it beneficial impact on the environment.

In the MDI production concept, the suppliers are chosen in a way to reduce costs, logistics and freights. All the purchases are managed at the MDI central purchasing unit, to beneficiate from the advantages of bulk buying."

One of the problems traditionally associated with alternative fuels, which all seem to admit we need, is Distribution. For many alternative fuels the Distribution chain is too expensive or too difficult to build. Well, air compressors are not too difficult to build and distribute. The electric power grid to run them is already there. What about an on site solar-powered air compressor? Very good in some areas which would then not have to import and burn fossil fuels.

http://www.mdi.lu/english/concept.php

Another way to consider this is in Agriculture:

Grow a carrot in California on land irrigated with Subsidized Federal Water and then truck that carrot to Massachusetts on Federally Subsidized Roads. Add in some cost for pollution, cost of illegal foreign wars to secure the OIL to do this. Probably some cost of political corruption in here also.

Grow the same carrot in Massachusetts and sell it locally.

Even if the selling cost of the carrot is the same, the actual, real cost of the carrot is not.

So, even if Air Propulsion is the same cost of gasoline, that is only one factor. For proper economic analysis, one has to examine the whole picture of auto production, fuel production and distribution and the geopolitical consequences of what Propulsion system is adopted.

[Penguin]

Re: French Air-powered Car To Trials

Hmmm.

Eleven years of higher education in mechanical engineering can be boiled down to three slightly breezy takes on the laws of thermodynamics:

1) You can't win.
2) You can't even break even.
3) You aren't allowed to quit.

In the end if you are using electricity to compress air you will always end up losing a goodly portion of the potential through losses.... from the initial power source which stand stands a good chance of being a nice old fashioned coal fired power plant. And they run about 30% efficient.

This thing has no chance of being as efficient as a nice new high speed small bore turbo diesel which run a tad over 40%. Now that is an idea who's time has come. And there are some beautiful ones coming down the pike. GM's new 4.5 turbo diesel is masterfully done. I pray they get a chance to introduce it to the public.

Will

[we_are_toast]

Re: French Air-powered Car To Trials

You can look at te MDI Bench Tests for yourself -- Energy audit carried out by the department of energetics of l’Ecole des Mines of Paris (July 2003)

possible autonomy corresponding to urban usage (between 117 to 146km (73 to 91miles)) taking into account typical speeds from 20 to 50km/hr (12.4mp/hr to 31mp/hr). At high speed, the autonomy will be lower. ...

To move the project from the design stage to the manufacturing process, a lot of development work is needed in order to reach the level of efficiencies required for the forecasted autonomy....

it shall be underlined that the CAT car concept permits to use free cooling due to the air low temperature (-40°C) at the air exhaust.

I see several difficulties with the concept.

The performance of electric cars, given the weight of this car, seems to be at least as good.

Cars have electrical systems that reduce the efficiency of this vehicle.

Compressing air to these extremely high pressures is not easy and requires a great deal of energy. I'm not sure a net energy analysis would reveal any saving in the CAT car. I agree with Penguin about the efficiencies of compressors.

That -40C exhaust could be a real problem in humid climates. I don't know how you avoid ice build up on several components on the vehicle.

I'm also wondering about the noise it makes. I assume it sounds like a steam engine and any attempt to muffle the noise would reduce it's efficiency considerably.

I'm always in the market for rechargeable energy storage systems, so I'll be looking at this in more detail.

[Munger]

Re: French Air-powered Car To Trials

CharlesTMungerFan -

I am absolutely a rank layman on the topic you are discussing, but I think you blew off Rajiv's recommendation that you read that report and digest it. Your dismissal seemed a little casual to this reader. Leaves me concluding that Rajiv's argument is being a mite more scrupulous.

Respectfully.



Originally Posted by Rajiv
You can look at the MDI Bench Tests for yourself -- Energy audit carried out by the department of energetics of l’Ecole des Mines of Paris (July 2003)

I didn't mean to sound casually dismissive. I did look at the report, as well as other academic papers on the topic. The MDI test summary however is not really up to the standards of an academic paper. For one thing, it does not mention the car's weight - making distance comparisons essentially meaningless. Figuring out a ballpark theoretical maximum for the stored energy source to determine what a compressed air vehicle is capable of if perfectly implemented is what I was going for.

[petertribo]

Re: French Air-powered Car To Trials

This thing has no chance of being as efficient as a nice new high speed small bore turbo diesel which run a tad over 40%. Now that is an idea who's time has come. And there are some beautiful ones coming down the pike. GM's new 4.5 turbo diesel is masterfully done. I pray they get a chance to introduce it to the public.

Will

Possibly, in terms of Propulsion, it is less efficient, though efficient means different things also. (Efficient in the City as opposed to highway, efficient because it uses local fuels, the French have nuclear Power but no Oil. Efficient also applies to other economic factors.)

That aside, you have only addressed the issue in terms of so-called mechanical engineering. Your post fails to address MDI's other cost factors and benefits, producing locally, using an energy system in part which is already in place, cost of OIL wars, costs of political corruption, etc. That's the trouble with mechanical engineering, economics, medicine, the folks who learn this stuff can't see a holistic picture.

As a perfect example, I live in a region which exports large quantities of natural gas but imports oil to refine into gasoline. Well, you cannot buy a car around here designed to run on natural gas nor will you find a distribution network. The OIL/AUTO/WAR cartels have decided that is the way it is. So, maybe time to look just beyond engineering.

I prefer products engineered for my situation not products where it is the Cartels which dictate the engineering. GM has been an obstacle to innovative transportation for decades. What was good for GM was no good for America. You pray that GM which is now a drain and a millstone on the taxpayer by given a chance to continue in their inefficient, bankrupt ways. Finally, this time, GM promises, we have it! Hmmm.

Good for the French if they see a way to bust up these Cartels and generate economic benefit and production in their own country. Too bad we don't have more of this type of thinking in America. Maybe then we could rebuild our manufacturing sector.

[Penguin]

Re: French Air-powered Car To Trials

The big picture? Like the fact that our underlying electrical infrastructure is incapable of providing the energy requirements of automobiles?

No, the big picture is what eludes those who tout each new revision of using old fashioned combustion to power a secondary power source. Most times either electric or pneumatic. That's the trouble with those who know nothing of engineering making policy decisions. They come up with inefficient and unusable ideas and waste billions trying to fit a square peg into a round hole.

Electric cars come to mind. If there has ever been a more wasteful use of natural resources I don't know what it could possibly be. On a first or second law basis. You start out with the efficiency of a coal fired power plant and then throw away a bit on your high voltage transport. Then you throw away ever larger chunks in your local grid, your household wiring, and finally an expensive and inefficient storage battery. Not to mention you have to put it all together in a package that would scarcely pass a 5 year old's soap box derby car as regards safety just to let it get out of its own way.

And in the end call it progress.

I'd a damned sight more rather see us go all the way back to external combustion engines powered with steam as go through that morass. At least with those you don't have to spend a half trillion updating the power grid to make it all work.

As far as the auto manufacturers go, I'll stack our guys in Detroit up against anyone in the world when corrected for deliberately debauched currency and trade barriers. The FIRE economy put those guys in front of a firing line. They were the fall guys. And let's not mice words, when you talk about 'labor costs' and inefficient plants you are talking about pensions. In the end the labor costs of Japanese and American auto workers is pretty comparable.

The difference is that we let them establish plants in this country without correcting for legacy costs.

Before you lecture me on the idiocy of Detroit maybe you should go back and review how trade policy was manipulated on both ends to produce the trade deficit... so that those dollars could be used to purchase bonds and keep that 'strong dollar' that our politicos love to tout. It's called mercantilism. In the end that is at the root of our woes. That's where the money came from. Recycling those dollars made Wall Street rich and financed these asset bubbles that keep popping up.

Try importing a shiny new D-8 from the Great Yellow Father into China and then get back to me on how trade between these two countries is 'free'.

Will

PS: After going back and rereading your post and mine it appears I might have come across more strident than I intended. Sometimes in my writing I do that. My apologies if it appears I took out the hammer and tongs on this post. It was not my intent to do so and if you took it that way I offer an apology. Actually I quite enjoy discussing new technology that is in my field. So few have even a passing interest in such things.

[Jam]

Re: French Air-powered Car To Trials

I think using a formula mechanically without understanding what it means! See my response to Metalman above

Rajiv, this comment was completely uncalled for.

For ideal gas (which, I believe, is a reasonably good approximation for air in this case) the following holds:

p V = n R T (1)

where p is the pressure, V is the volume, n is the number of moles, R = 8.314 J K⁻¹ mol⁻¹ is the gas constant, T is the absolute temperature (in K).
For isothermal expansion (compression), the right-hand-side is (by definition) constant. I.e. pV=const. This means that increasing the pressure by a factor, say, 300 reduces the gas volume by the same factor.
The differential amount of work dW done on the gas to compress it by a differential amount of volume dV is

dW = - p dV. (2)

To get the total amount of work, we integrate the above equation between V1 (initial volume) and V2 (final volume) to get

W = - integral_V1^V2 p dV. (3)

But, according to (1), p V = n R T = const, so p = n R T/V. Substituting this to (3) produces

W = - n R T integral_V1^V2 dV/V,

which can be easily integrated and yields

W = - n R T natural_log (V2/V1).

By using (1) again, we can express W in terms of p.

W = n R T natural_log (p2/p1),

where p2 is the final pressure, and p1 is the initial pressure of the gas. At ambient temperature T = 300 K, and for 1 gram of air (n ~ 1/29 moles), the factor n R T becomes ~86 J/g (that's joules per gram). At 300 compression ratio, i.e. p2/p1 = 300, natural_log (p2/p1) = 5.7. So, there you have it

W = 86 * 5.7 = 490 J/g = 0.49 kJ/g

This is how much energy you have to use to (isothermally) compress air from 1 atm to 300 atm. This is also the upper limit of how much energy you can extract from it. It also happens to be 1/100 the energy density of gasoline. Which is a point CharlesTMungerFan was trying to make, and which I hereby corroborate.

Now, Rajiv, if I were to reciprocate with a nasty comment like yours, I would say that for a living you mindlessly (mechanically) pass publications that fail to meet the standards of an academic paper as research. However, I am not going to do this as, I have to admit, I really enjoy reading the vast majority of your posts. So, let's not make it personal, and agree that indeed the energy density of compressed air is 1/100th that of gasoline. Of course, how (efficiently) you use that energy is a completely different matter. Indeed, if you can use it 5 times as efficiently (80% for compressed air vs. 16% for gasoline), then the ratio narrows down to 1/20th. You can split the factor of 20 into 10 times the tank size (weight, actually) and 1/2 of the range, or 5x the tank size and 1/4 of the range, or any other way you like it. However, the fact remains that you get considerably less utility for more storage space (mass) with compressed air as compared to gasoline.