Air Car: India's Eco-Friendly Auto

[baywax]

Here's a new form of locomotion using compressed air to turn the engine's pistons. A fill up costs about 2 dollars (2 days wages in India)

Air-Car Ready for Mass Production

by Bob Ewing

The world's first commercial compressed air-powered vehicle is rolling towards the production line. The Air Car, developed by ex-Formula One engineer Guy Nègre, will be built by India's largest automaker, Tata Motors.

The Air Car uses compressed air to push its engine's pistons. It is anticipated that approximately 6000 Air Cars will be cruising the streets of India by 2008. If the manufacturers have no surprises up their exhaust pipes the car will be practical and reasonably priced. The CityCat model will clock out at 68 mph with a driving range of 125 miles.

http://green.yahoo.com/index.php?q=node/315

 

[AlephZero]

Hmm... so how big is the air tank? An very efficient IC engine in a small vehicle might use about 1gal of gasoline for that range and performance.

The volumetric energy density for compressed air is going to be a lot smaller than gasoline, even though the engine might be more efficient at low speed, similar to a positive displacement steam engine - no need for a gearbox, etc.

 

[baywax]

Hmm... so how big is the air tank? An very efficient IC engine in a small vehicle might use about 1gal of gasoline for that range and performance.

The volumetric energy density for compressed air is going to be a lot smaller than gasoline, even though the engine might be more efficient at low speed, similar to a positive displacement steam engine - no need for a gearbox, etc.

Pretty wild. I don't have any of these specifications. There may be a website. I thought that perhaps in the future there will evolve a better compression mechanism and that they may also be able to compress on the go and store it in a second tank. This may, however, add more weight. Are there composites that are pretty light that would still hold compressed air?

mileage and general running
Much has been said and written about the mileage of our vehicles and there has generally been a lot of unfounded speculation about the use of compressed air.

We have never claimed that the thermodynamic graphs of our engines would be adiabatic (nor are they isothermic). Mileage presents no problem - the volume and pressure of air in the car can be increased considerably. (by changing the tank size or the air pressure). The data published at this link, should help to re-establish the truth and give definitive information on these two points.

Distribution and valves
To ensure smooth running and to opitimize energy efficiency, our engines use a simple electromagnetic distribution system which controls the flow of air into the engine.

http://www.theaircar.com/howitworks.html

There's a ton of information on this site... this is just a quick quote from "how it works". Of course it is the manufacturer's website!

edit. Here's and interesting compression industry leader's website with some of the current and expected advances available in air compression explained.

http://www.plantservices.com/articles/2005/257.html

 

[NateTG]

Compressed gas is a relatively inefficient way to store energy. As a consequence, for net efficiency improvement, the compression plant would have to have some pretty spectacular properties.

At least in theory, compressed air engines do have the advantages that they can be very inexpensive, and are likely to be much better than 2-stroke engines vis-a-vis polution.

In practical terms, I'd expect that compressed air cars are going to be an improvement over electrical cars in terms of practicality since they're more conducive to fast refilling, and (hopefully) cheaper, but, at the same time, they're going to be less efficient.

 

[q3snt]

From the Yahoo article:

The folks making the Air Car are already working on a hybrid version that would use an on-board, gasoline-powered compressor to refill the air tanks when they run low. Negre says that technology could easily squeeze a cross country trip out of one tank of gasoline.

What would be the point of having a gasoline engine to compress the air which will then run the car? If you are going to be burning gasoline anyways, why not just run the motor on it? The more changes the energy has to go through the less efficiency you are getting, right?

 

[russ_watters]

The primary benefit would be to run the gas engine at it's optimal efficiency all the time. But as NateTG said, air is a bad way to store energy, so I don't see that as being a better idea than a gas/electric hybrid.

 

[brewnog]

A gasoline engine could be employed for medium/high speed driving, where it's operating around it's peak efficiency. Round town, and in traffic jams, the compressed air drive could take over, much in the same was as an electric hybrid, thus reducing city pollution.

Don't really see any huge advantage though.

 

[baywax]

A gasoline engine could be employed for medium/high speed driving, where it's operating around it's peak efficiency. Round town, and in traffic jams, the compressed air drive could take over, much in the same was as an electric hybrid, thus reducing city pollution.

Don't really see any huge advantage though.

No need for big batteries may be an advantage over the alternative. Not a complicated engine compared to today's hybrid and fuel cell technologies. But it won't do 120 miles an hour. Not sure what the torque is. Thanks for the input here.

 

[out of whack]

Compressed gas is a relatively inefficient way to store energy.

What are the various alternatives for storing energy efficiently, considering the weight, size and durability of the device? Batteries, for example, are heavy and don't last very long compared to an air tank that lasts until it rusts through. What about mechanical coil springs you find in toy cars? They probably don't scale up to a good weight to energy ratio... What else is there?

 

[q3snt]

What else is there?

I know flywheels http://en.wikipedia.org/wiki/Flywheel_energy_storage are known for storing energy very good.

When used in vehicles, flywheels also act as gyroscopes, since their angular momentum is typically of a similar order of magnitude as the forces acting on the moving vehicle. This property may be detrimental to the vehicle's handling characteristics while turning. On the other hand, this property could be utilised to improve stability in curves.

But they might be expensive, or they might be impractical for some other reason.

 

[baywax]

I know flywheels http://en.wikipedia.org/wiki/Flywheel_energy_storage are known for storing energy very good.



But they might be expensive, or they might be impractical for some other reason.

The old 1973 SAAB station wagon had a fly wheel in it. If they don't anymore its because they weren't efficient economically or otherwise. Building and trashing big batteries is environmentally inefficient. Finding and the refining of oil has proven to be environmentally inefficent along with the many inefficent ways it is used in inefficent motors, which maintain its production value. Hydrogen fuel cell engines have yet to prove their worth and I suppose an engine run by compressed air has some proving to do too. Electric cars were crucified but may be resurrected but I have no clue as to how efficient they are. There may be some of the same environmental problems with energy storage as hybrids.

 

[Asiadeep]

An extremely interesting idea which I suppose wasn't feasible until the development of the more efficient compressed-air engine. We'll see if this picks up and I do have to say, its a great way to get pollution out of the cities.

 

[russ_watters]

Thermodynamics puts hard and fast limits on the efficiency of compressors and compressed-air engines. It isn't ever going to be an efficient way to store energy.

 

[baywax]

Thermodynamics puts hard and fast limits on the efficiency of compressors and compressed-air engines. It isn't ever going to be an efficient way to store energy.

Here is a link to a good study out of Switzerland with some more facts concerning the "Thermodynamic Analysis of Compressed Air Vehicle Propulsion"

Abstract
The fist compressed air vehicles were built by Andraud and Tessié du Motay in Paris between 1838 and 1840. Since then the idea has been tried again and again, but has never reached commercialization. In recent years the French developer MDI has demonstrated advanced compressed air vehicles. However, the claimed performance has been questioned by car manufacturers and automobile expert. Basically, when referred to ambient conditions, the relatively low energy content of the compressed air in a tank of acceptable volume is claimed to be insufficient to move even small cars over meaningful distances

On the other hand, another air car developer claims to have driven 184 km on one 300 Liter filled with air at initially 300 bar pressure. Obviously, there are issues to be resolved, not by heated debates, but by an analysis of the thermodynamic processes involved. This is the aim of this study.

(pdf)
...continued...

http://www.efcf.com/e/reports/E14.pdf

This is an excellent analysis of the whole idea. There are several comparisons of various compression techniques with graphs showing the thermodynamic efficiency of each method.

I'm not sure if this study was written before or after Tata Motors of India came up with their little car with an air compression engine that can do approx. 68 m per hour for approx. 184 m until requiring a re-fill of... air.

 

[russ_watters]

I only skimmed it, but it seems like a good analysis and the bottom line is a thermodynamic efficiency of 40% using a four-stage compressor with intercooling and 4 stage turbine to recover the energy. The efficiency of a generator -> battery-> motor system in a conventional hybrid is upwards of 80%. So I don't see how this could be considered a viable technology.

 

[baywax]

I only skimmed it, but it seems like a good analysis and the bottom line is a thermodynamic efficiency of 40% using a four-stage compressor with intercooling and 4 stage turbine to recover the energy. The efficiency of a generator -> battery-> motor system in a conventional hybrid is upwards of 80%. So I don't see how this could be considered a viable technology.

The Air Car has obviously been considered efficient enough to build 6000 of them. Here's a page on the company website with some of the early test results of the prototype "Taxi". There seems to be room for improvement in terms of energy efficiency. Just look at how gas vehicles have changed over the decades.

This page has specs on energy, amount of compression, size of tanks etc... Also, weight has been reduced by using carbon fiber air tanks that meet safety specs.

http://www.theaircar.com/tests.html

Here's their page on thermodynamics and mileage:

http://www.theaircar.com/data_sheet.html

Here are the press-releases on the Air Car found in many major news sources but not really heard about in NA.

http://www.theaircar.com/media_articles.html

 

[russ_watters]

The Air Car has obviously been considered efficient enough to build 6000 of them.

That doesn't mean anything at all.

There seems to be room for improvement in terms of energy efficiency. Just look at how gas vehicles have changed over the decades.

You're basically saying that you don't accept that the laws of thermodynamics are real. And no, while gas vehicles have changed a lot over the decades, the thermodynamic efficiency has not increased substantially. The fact that a 2007 Honda Civic gets better fuel economy than a 1970 Chevelle has very little to do with the thermodynamics of an Otto cycle engine.

 

[baywax]

That doesn't mean anything at all. You're basically saying that you don't accept that the laws of thermodynamics are real. And no, while gas vehicles have changed a lot over the decades, the thermodynamic efficiency has not increased substantially. The fact that a 2007 Honda Civic gets better fuel economy than a 1970 Chevelle has very little to do with the thermodynamics of an Otto cycle engine.

I admit that I don't know enough about the laws of thermodynamics.
What I'm pointing out is that the car maker is working with what they can get out of the available energy efficiency that comes with compressed air. Isn't that what technology is all about? Doing more with less and that sort of thing.

 

[wolram]

A big problem with compressed air is keeping it dry, free of water, also seals
degrade, a typical linear cylinder is due for refurbishment after about 2 million cycles, beyond that the performance can not be guaranteed.

 

[AlephZero]

This page has specs on energy, amount of compression, size of tanks etc... Also, weight has been reduced by using carbon fiber air tanks that meet safety specs.

http://www.theaircar.com/tests.html

If I understand that page right, they actually managed to travel 7.22 km before they ran out of air. Then they thought of a list of reasons why the 7.22 km was really 242.10km, honest. That's quite an impressive extrapolation!

The term do describe this sort of thing in aviation is "a paper aeroplane".

The other "technical" web pages are fairly content-free, as well.

 

[baywax]

A big problem with compressed air is keeping it dry, free of water, also seals
degrade, a typical linear cylinder is due for refurbishment after about 2 million cycles, beyond that the performance can not be guaranteed.

Yeah I wondered about condensation with these things.

 

[baywax]

If I understand that page right, they actually managed to travel 7.22 km before they ran out of air. Then they thought of a list of reasons why the 7.22 km was really 242.10km, honest. That's quite an impressive extrapolation!

The term do describe this sort of thing in aviation is "a paper aeroplane".

The other "technical" web pages are fairly content-free, as well.

It does seem a bit sparce. Is this a hoax? Do we need to send this to the Scepticism and Hoax forum or what?!

 

[russ_watters]

I admit that I don't know enough about the laws of thermodynamics.

The page you provided has a very good description of the thermodynamics. It isn't altogether hard to understand, just a little involved.

The basic principle that they are up against is that when you compress air, it heats up. A lot. That heat is unusable energy (in a single-stage compressor). The result is that even an extremely good compressor and turbine (the example used four stages, the car is two) yields you 40% capture-> storage-> useage efficiency. That's a fundamental problem that is utterly impossible to overcome. It's the same type of problem that has car engines of 30 years ago and car engines of today both being roughly 30-40% efficient thermodynamically. You'll never see a 50% efficient internal combustion car engine.

The only way to get a higher efficiency is to not use a thermodynamic process to convert the fuel energy to mechanical work, but to use an electrochemical process: fuel cells.

What I'm pointing out is that the car maker is working with what they can get out of the available energy efficiency that comes with compressed air. Isn't that what technology is all about? Doing more with less and that sort of thing.

Yes, that's all fine, but if it isn't useful, why do it? They aren't doing a science fair project, they are trying to make a profitable company. The reason I hate this sort of thing, though, is that through misleading marketing, they can scam the public and the government into investing in the company, making the owners rich regardless of if they ever make a marketeable product. That, to me, is fraud.

There's a big red fraud flag on the homepage:

The company is financed by the sale of manufacturing licences and patents all over the world.

What? They don't make their money by selling cars? That's like the infomercials you see on late night tv selling get rich quick schemes - they sell you a book that tells you that to get rich quick you should sell books promising to make people rich by selling books to teach people to sell books to get rich.

 

[baywax]

The page you provided has a very good description of the thermodynamics. It isn't altogether hard to understand, just a little involved.

The basic principle that they are up against is that when you compress air, it heats up. A lot. That heat is unusable energy (in a single-stage compressor). The result is that even an extremely good compressor and turbine (the example used four stages, the car is two) yields you 40% capture-> storage-> useage efficiency. That's a fundamental problem that is utterly impossible to overcome. It's the same type of problem that has car engines of 30 years ago and car engines of today both being roughly 30-40% efficient thermodynamically. You'll never see a 50% efficient internal combustion car engine.

The only way to get a higher efficiency is to not use a thermodynamic process to convert the fuel energy to mechanical work, but to use an electrochemical process: fuel cells. Yes, that's all fine, but if it isn't useful, why do it? They aren't doing a science fair project, they are trying to make a profitable company. The reason I hate this sort of thing, though, is that through misleading marketing, they can scam the public and the government into investing in the company, making the owners rich regardless of if they ever make a marketeable product. That, to me, is fraud.

There's a big red fraud flag on the homepage: What? They don't make their money by selling cars? That's like the infomercials you see on late night tv selling get rich quick schemes - they sell you a book that tells you that to get rich quick you should sell books promising to make people rich by selling books to teach people to sell books to get rich.

Excellent response Russ. You mentioned fuel cell technology and I notice that Ballard Fuel Cell Systems bought or is buying the license to the technology from Manhattan Scientifics.

Manhattan Scientifics Licenses Fuel Cell Patents To Ballard

Non-Exclusive Agreement Opens Way For Additional Licensing Opportunities

http://www.prnewswire.com/cgi-bin/stories.pl?ACCT=104&STORY=/www/story/05-09-2003/0001943735&EDATE=

Also, Mercedes, Ford, GMC and others have bought licences or made agreements with Ballard to use similar technology or to buy the systems directly. Yet, there are very few of the vehicles on the road. I have been so optimistic about Fuel Cell engines in the past but my optimism slips everytime there are set backs or the stock price dumps. Is this another scam? Are there technological leaps yet to be made or is the technology being held back by a needy and greedy oil cartel?

I noticed another story about the international flight regulator (like I'm going to find the article again!) putting a date like 2050 for airlines and airlship builders to have their planes flying on "green" and clean energy.

So I googled for fuel cell jets and jet engines and here's what I found.

Hydrogen fuel cell powered Hyfish jet takes flight
Posted Apr 19th 2007 11:48AM by Donald Melanson
Filed under: Misc. Gadgets, Transportation

http://www.engadget.com/2007/04/19/hydrogen-fuel-cell-powered-hyfish-jet-takes-flight/

But, like the Ballard Bus that clicked a whirred around on back streets during the last 20 years and their prototypes, this Hyfish Jet is just another prototype. More hype? Let's get this stuff off the ground. There's also the possiblility that the fuel cell has already been perfected by the military sector but is "under wraps" for obvious reasons.

 

[NateTG]

I only skimmed it, but it seems like a good analysis and the bottom line is a thermodynamic efficiency of 40% using a four-stage compressor with intercooling and 4 stage turbine to recover the energy. The efficiency of a generator -> battery-> motor system in a conventional hybrid is upwards of 80%. So I don't see how this could be considered a viable technology.

The fact is that compressed air is a very popular power storage and transportation method in shops and construction sites.

At current gas prices, over the life of te car, I think it's still cheaper to buy a non-hybrid and put the savings against gasoline. Air engines can theoretically be very simple for easy manufacturing and reliability and have high power density to keep material cost and vehicle weight down. It seems very possible to me that an air-powered car could end up being cheaper than a gasoline powered one over the life of the car.

There's also pollution containment. Air cars have the advantage that the fuel burning (or whatever) takes place at a stationary location which means that economies of scale can be brought to bear both on the production and pollution handling.

Reduced chemical pollution is also a potential benefit. Because the fuel production process is chemically cleaner, air car infrastructure is much more amenable to alternative energy production methods. Thi is especially true if air motors can become a viable alternative to conventional two-stroke motors in the third world.

 

[russ_watters]

The fact is that compressed air is a very popular power storage and transportation method in shops and construction sites.

That's true, but that doesn't have anything to do with whether or not they would be good to power cars.

At current gas prices, over the life of te car, I think it's still cheaper to buy a non-hybrid and put the savings against gasoline.

It depends on the assumptions in the calculations, but your basic point is valid - it isn't a clear benefit.

Air engines can theoretically be very simple for easy manufacturing and reliability and have high power density to keep material cost and vehicle weight down. It seems very possible to me that an air-powered car could end up being cheaper than a gasoline powered one over the life of the car.

I'd be surprised if any of that were true, but it is tough to evaluate until someone actually puts one into production.

There's also pollution containment. Air cars have the advantage that the fuel burning (or whatever) takes place at a stationary location which means that economies of scale can be brought to bear both on the production and pollution handling.

That's true only if the efficiency is high enough that it doesn't require burning 3 times as much fuel (or if the burning is 3 times cleaner). That's a tough sell and in any case, pollution isn't the only issue with fossil fuels: there's also the limited supply issue.

Reduced chemical pollution is also a potential benefit. Because the fuel production process is chemically cleaner, air car infrastructure is much more amenable to alternative energy production methods. Thi is especially true if air motors can become a viable alternative to conventional two-stroke motors in the third world.

I could see an argument for having a wind turbine power a compressor directly and then utilizing that in pneumatic devices. But with the current levels of demand for power, I'd rather see the energy go into the power grid.

 

[mheslep]

I only skimmed it, but it seems like a good analysis and the bottom line is a thermodynamic efficiency of 40% using a four-stage compressor with intercooling and 4 stage turbine to recover the energy. The efficiency of a generator -> battery-> motor system in a conventional hybrid is upwards of 80%. So I don't see how this could be considered a viable technology.

If comparing the efficiency of the whole air-car system shouldn't you do likewise w/ a gas-hybrid and instead say: combustion-engine ->generator ->battery ->motor which is then limited by a Carnot heat engine efficiency.

 

[PRDan4th]

I think a compressed natural gas car with a new engine technology using a combustion turbon with a turbo/expander for air compression would be a better way to use the high pressure storage tank required for the air car.

 

[russ_watters]

If comparing the efficiency of the whole air-car system shouldn't you do likewise w/ a gas-hybrid and instead say: combustion-engine ->generator ->battery ->motor which is then limited by a Carnot heat engine efficiency.

No, both systems contain an internal combustion engine, so you can just cut it out of the equation. It isn't hard to put back in, though, if you want: just multiply both efficiencies by .35.

 

[russ_watters]

I think a compressed natural gas car with a new engine technology using a combustion turbon with a turbo/expander for air compression would be a better way to use the high pressure storage tank required for the air car.

Ya know, that's acutally a good point - people are looking into pressurized tanks for storage of hydrogen or methane for burning in an ICE or fuel cell. But they are still running into the energy density problem even though their compressed gas burns!