The Air Car - A Breath Of Fresh Air Or A Waste Of Breath ?
Posted by Big Gav on December 17, 2007 - 7:18pm in TOD: Australia/New Zealand
Topic: Alternative energy
Tags: air car, mdi, transportation [list all tags]
The primary impact of peak oil will be felt on our transportation systems. As road transportation is the primary consumer of oil, this is where we will need to make the most changes in order to adapt to less available oil. There are a number of ways of adapting - most, if not all, of which have been discussed at length in the peak oil blogosphere. These include expanding mass transit systems, redesigning cities and towns to make them easier to walk or cycle around (or combining both of these approaches in "transit oriented development"), making greater use of electric cycles (or mopeds), using lightweight materials in vehicle construction, and - most commonly - switching to electric vehicles (particularly, in the medium term, plug-in hybrids).
One variation on the oil free car alternative is the "air car", which is powered by compressed air. The Age recently reported that IT MDI-Energy will be setting up a manufacturing plant in Melbourne, with cars expected to go on sale next year for less than $8000 and with running costs "80% lower than current comparable vehicles" (2 L per 100 km).
All of this sounds very promising (and the company promotes it as the solution for both peak oil and global warming). The question is - is it for real ?
The company is claiming that the vehicles will be able to attain speeds of up to 110 kilometres an hour, and travel 150 kilometres on compressed air alone. The Age article also mentions another (hybrid) mode of operation where the air is heated using a fuel source, such as ethanol or diesel, which would make it "possible to travel from Perth to Brisbane without refuelling".
The car is refuelled by plugging it into the compressed air supply found at most service stations, and founder Louis Arnoux is claiming that the "engine technology could also be used to power homes". In other words, it is another way of implementing the vehicle to grid (or V2G) concept - which would be an interesting development as one of the main obstacles for this idea (once plug-in hybrids appear in significant numbers) is the impact of constantly discharging and recharging on battery lifespans (though recent developments in this area are promising too).
Compressed air is similar to hydrogen - it is an energy storage medium, not an energy source. Critics point out that using compressed air simply shifts energy production from oil based engines to power stations - usually coal fired ones, particularly in Australia. On the other side of the ledger, compressed air is a safe, well-known storage mechanism (already in large scale use to store power produced by wind farms, for example), and the energy generation infrastructure can (and hopefully will) be converted from fossil fuel based sources to cleaner alternatives over time.
The Air Car was created by MDI (Moteur Developpement International) which is headquartered in Luxemburg, while the prototype factory is in the south of France. Originally conceived by former Formula 1 engineer Guy Negre back in 1991, the official names for the “Air Cars” are the OneCAT, CityCAT and MiniCAT. The OneCAT is expected to sit three or five people, with the MiniCAT and CityCAT models expected to follow.
MDI recently signed a deal with India’s Tata Motors, to build the air-powered vehicles in India. Zero Pollution Motors is looking to market the car in the US, and the Thai government has also invited Tata to manufacture the car in Thailand. A Colombian company (MDI Andina S.A) is also looking to produce the cars and sell them in Latin America.
The company has been talking about producing cars since at least 2000, so it is worthwhile remaining skeptical until cars start rolling off a production line somewhere.
WebHubbleTelescope had a brief look at the Air Car back in 2004.
The Air Car has gotten the press excited on and off over the years. The French design, which has received the most publicity, uses compressed air as an energy delivery mechanism. It has the potential for providing a clean-burning solution, but as usual it takes net energy to compress the air. No free lunch, unless wind or solar energy are involved to run the air compressors. And even there, we require energy to make the windmills and solar conversion devices.
As a sanity check here are two ways to calculate the energy value of 1 liter of compressed air. Remember that the gold standard is 1 GJ/30 liters for gasoline (or 33,000,000 joules/liter). First, if you compress air completely you actually get liquid. So we take the energy value of liquid nitrogen (air consists of 70% nitrogen by volume).
1. Energy Density/Specific Energy of liquid nitrogen = 320 KJ/l or 320,000 joules/liter
2. Heat of Vaporization of liquid nitrogen = 161 KJ/l or 161,000 joules/liter (to double-check the above value)Looking at specific energy, this is at best 100 times less energy content than gasoline. On the plus side, the transfer to mechanical power is better than for gasoline (burning gas generates much wasted heat). Granted that advantage, we still have to generate the compressed air by using energy, and to top it off, we also have much worse energy density (i.e. energy per volume) than gasoline. You understand why consumers and corporations like gasoline (little energy overhead to extract a free lunch).
James Fraser at The Energy Blog had a look at the air car earlier this year when the Indian deal was announced, coming to the following conclusion:
This technology competes with the electric car. The claimed advantage of compressed air over electric storage is that it is less expensive, has a faster recharge time and pressure vessels have a longer lifetime compared to batteries. Both technologies have hurdles to overcome, demonstrating that the air engine/compressed air system is as light, efficient and cheap as available electric motors/batteries. The main issues to me are that the air engine has not been proven to be dependable and advanced batteries are still too expensive. ...
A discussion of the energy efficiencies of an air engine vehicle vs an electric vehicle would breakdown into the efficiency of the air compressor and air engine vs the efficiency of batteries and motors in the electric car, which I am sure the electric car would win. However because of the potentially low initial cost, low maintence cost and low operating cost compared to a fossil fueled vehicle the "air car" could find a niche market if it could be marketed before low cost batteries are available.
The Australian operation, IT-MDI Energy Pty Ltd, is a merger betweeen MDI and IT Mondial, Louis Arnoux’s IT business. The IT MDI-Energy venture has other ambitions besides transport, with its (in my mind, very confusing) website detailing plans to provide home power generation (shades of the key to Richard Smalley's "distributed energy grid" idea) and even broadband internet services in a “green” manner, using a combination of solar power and some sort of cogeneration technology. While the air car idea seems to have quite a lot of history behind it, much of the rest smells a lot like vapourware based on the information on the website.
When the article in The Age came out, Kyle Schuant posted a few back-of-the-envelope calculations to The Bullroarer comparing the air car to a small petrol fuelled car in terms of fuel costs and carbon emissions, in which the air car fared pretty well.
If I remember my high school physics and chemistry right, the energy E required to compress air at 25C is,
E = 110,000 x ln (P1/P2) /m3/mol
There are about 45mol air in 1m3, so,
E = 110,000 x ln (P1/P2) /m3
This howstuffworks article tells us that an air car tank might have 300lt at 4,561psi, which is 29,999,087.707 - call it 30,000 kPa. Atmospheric pressure is 101.3kPa. 300lt at 30,000kPa will be 90,000lt at atmospheric pressure, or 90m3. And so we get,
E = 110,000 x ln (30,000 / 101.3) x 90
= 110,000 x 5.69 x 90
= 56,331,000J
which is 15.6kWhrHowever, a company which supplies air compressors tells us that "Most systems typically waste 25 to 50 percent of the energy required to generate compressed air that actually provides useful work."
Let's be optimistic and assume that with lots of air cars zooming around, service stations will buy the most efficient (expensive) compressors. So we get just a 25% loss. This brings us to 20.9kWhr.
Let's round it up to 21kWhr to refill the tank. Again, this isn't the air car referred to in the article, but it gives us an idea of the order of magnitude.
21kWhr to travel 200km.
A regular small city car gets about 10km/lt. Petrol costs about $1.30/lt, and causes 2.32kg CO2e/lt. So to go 200km in a regular car would cost $26 and cause 46.4kg CO2e in emissions.
Electricity from coal cost $0.1355/kWh and 1.21kg CO2e/kWh, so the 200km journey would cost $2.85 and cause 34.9kg CO2e in emissions.
Electricity from wind costs $0.19/kWh and causes 0.04kg CO2e/kWh. So the 200km journey would cost $3.99 and cause 0.84kg CO2e in emissions.
The average Australian car is driven 15,000km annually. That'd be 75 refills, or 1,575kWh energy in all. That's not bad when the average household uses 6,000kWhr annually.
Presumably service stations could do things better than we could at home, since they can buy the big heavy and efficient equipment; if service stations supply so much compressed air, they'll start charging more for it, more than the power costs. Still, it seems that running it on compressed air will be significantly cheaper in money terms.
However, if the air is compressed by electricity got from coal, the greenhouse gas emissions will be comparable to simply burning petrol in the car.
Again, not perfect calculations, but the best we can do with the data we've got, and they give us an order of magnitude idea of the numbers involved.
There is another Australian company pursuing air powered vehicles - the Di Pietro Rotary Air Engine, which doesn't seem to have made much progress commercialising their technology, though it still appears in the press from time to time. From a recent ABC interview:
BLANCH : As the world wakes up to global warming, petrol prices rise and greenhouse gases pollute the atmosphere, what better than a car that creates zero pollution by running on nothing but compressed air? The dream started seven years ago for a Melbourne engineer, Angelo di Pietro, to advance his innovative air-driven 'Engineair' vehicle that he conceived, designed and developed and which could have an enormous impact on future motor-driven applications. I asked Angelo to list after zero-pollution, what he considered to be important improvements that his engine delivered over other motors.
ANGELO DI PIETRO : Our motor delivers high torque and low rpm, very high efficiency, low noise and it's a fraction of the weight of a traditional piston motor. It is cheaper to produce and is better for the environment, as less material and energy is used in its production.
BLANCH : So your motor is based on a rotary piston. How does your engine design differ from existing rotary engines?
ANGELO DI PIETRO : Uses a single rotary piston and pivoting dividers which runs almost frictionless.
BLANCH : Your motor's seven times smaller than the piston air motor currently in use, so what power does the engine develop with what about of compressed air?
ANGELO DI PIETRO: Although our motor is seven times smaller than the piston air motor, we develop much more power with considerable less energy, even by using our early motor's testing results of 2002, conducted by Monash University, we only use 770 litres per minute per horse power compared with the piston motor's 896 litres. We have advanced our technology today enormously and our scientific model predictions suggest that the new motor could be made at least four times more efficient for the same power output, compared to its commercial competitors.
BLANCH : So how do you get your motor to operate at a higher torque or with greater efficiency?
ANGELO DI PIETRO : By regulating air pressure and timing or manipulating the compressed air to perform the reverse function from when it was compressed.
BLANCH : You've designed the engine to be suited to a variety of applications and these range from commercial vehicles and motor scooters, buses, boats, trains and cars. Well that's a whole spectrum of transport, isn't it? So how does your engine adapt to such a range of vehicles?
ANGELO DI PIETRO : The engine can be scaled up or down in its size and will be built from different materials specific to each use, for example, carbon fibre or other plastics or even stainless steel for marine use. Our engine is best suited to a new generation of vehicles that can be built lighter as the need to build current heavier structures to support large heavy motors and all that goes with them is no longer required. This reduction in the weight of the engine and the elimination of many other components translates into fuel efficiency and economic benefits. ...
Cross posted from Peak Energy
Uh-oh, now someone will tell me that I didn't remember my high school physics right! Sorry, it was a long time ago and the only physics experiments I've done since then involved firing rifles.
It's probably worth mentioning that a 300lt tank is pretty significant. That's about the size of your average sedan's boot. Given the pictures we've seen of these prototypes, either the tank is cunningly hidden underneath, or else it's accidentally oops omitted from the image. Or perhaps the engine is magically as small as a walnut and the tank's in there.
I think it's an awesome idea if coupled with renewable energy, though an atrocious idea if coupled with fossil fuel generated electricity (better just to burn the stuff directly in the car). I'm just sceptical about the engineering and economics of it. They've had the better part of a decade to secure the patents, so there's no reason they can't put the technical details out there - except of course if it's just geek dreamware...
The idea of cars having accidents with a 3500psi container in each of the cars is a major concern. Have you ever seem the results of a hot water storage tank exploding due to the failure of the temp/pressure valve and faulty thermostat. It can destroy a house and the pressures here are substantially less than is proposed for the air car. Not a chance!
LPG is at a similar pressure and has trundled around in the back of cars for decades. Of course, they don't have 300lt tanks, but rather 30-75lt, but still.
I've yet to hear of a hot water system's explosion "destroying a house". The wiring or gas can go wrong and start a fire, but that's why - here in Victoria at least - they legally have to be outside the house.
Absolutely having all that air under pressure would be a safety concern. But so is having 40-75lt of petrol or LPG, travelling at 100km/h, and so on. We try to make those safe.
Me, I'd rather we were rid of cars entirely, even if they were powered by sunshine, strawberries, and pretty girl's smiles. But I'm not optimistic that'll happen any time soon, so instead I'm interested to hear of ideas like this - it's just a pity they always turn out to be some geek's wet dream.
I can assure you that 300l of hot water/steam can do a lot of damage if they explode. I used to work in the elect industry and have had quite a lot to do with how water systems. In NSW at least, it is quite legal to have HWS inside a house and they do make a good drying cupboard and also improve eff through lower losses.
I agree LPG is under high pressure but there have a few accidents but they are few.
However, it is only postponing the inevitable, we have to get off the car dominated society.
So they "do a lot of damage", they don't "destroy the house". Those are two very different things.
NSW is a dangerous and savage land. HW systems should be outside the house, not in it.
If we can use a high pressure flammable gas safely, then we can use a high pressure non-flammable gas safely.
I agree that cars suck. Here I rant about how and why I hate them ;)
Agreed on all counts :-)
Welding cylinders run 2000 psi+ and are trucked around regularly with safety.
Actually, they are exceedingly dangerous in a vehicle fire, especially acetylene which is not stored at very high pressure because it will spontaneouly explode.
In the UK nobody will go anywhere near a fire with welding cyliders involved - that includes the fire brigade.
Several times this year alone major motorway routes have been closed for twenty four hours after a vehicle has been left to burn itself out before anybody will go within several hundred metres of it.
http://www.youtube.com/watch?v=akqvaZ5J1aY&feature=related
Oh, they certainly have the potential to "destroy a house." But the trick is that with 40 gallons or so at 300psi and umpteen degrees...when the pressure is released - it flash boils. So you get that first crack in the water heater and it all turns into water vapor KAPOW! So the power there comes from 40 gallons of liquid turning into a gas - there's some serious expansion there. The MDI car's tank is designed to rupture in a certain way to direct the explosion and diffuse it as much as possible. At 3000 psi though, it's still a fricken bomb.
"The MDI car's tank is designed to rupture in a certain way to direct the explosion and diffuse it as much as possible."
One of the miracles of composite materials. CNG is also stored at this pressure on vehicles with few safety concerns, so given that air is a significantly less flammable gas I'm not so concerned.
Water? Outdoors? But it will all freeze solid in the winter! And in parts of fall and spring, too At least where I live it would. :) In the non-tropical parts of the world, the hot water heater is indoors and a matter of course.
LPG is at a similar pressure and has trundled around in the back of cars for decades. Of course, they don't have 300lt tanks, but rather 30-75lt, but still.
From Wikipedia:
Even taking the higher number for propane, 2.2 MPa is 13.5 times lower than the 30MPa used in the above calculation. 30MPa is 300atm. or the pressure exercised 3000 meters below sea level. An explosion of such a tank would be a dangerous thing to happen.
Let's assume that they can get 80% efficiency out of their expander, and they need a range of 150 miles, at about 100 watt-hours per mile. These are all optimistic assumptions.
So we're talking about most of 69 megajoules, the energy equivalent of 1/2 gallon of gasoline, released in a fraction of a second.
A better comparison may be - that's the energy equivalent of 36 pounds of TNT.
edit: corrected for higher efficiency
I am sure that there will be many on this thread who will do the simple math and also point out that for reasons of safety, short range, massive difficulties in repressurising and sheer inefficiency this is yet another example of why there are, as yet, still no adequate alternatives to gasoline or diesel for road transport.
It seems we have no option but to make gasoline somehow or other. This is why the only currently suitable alternatives to fuels from crude oil are the limited sources of ethanol, bio-diesel or gasoline from tar.
To give you some idea what all the potential alternatives are up against remember gasoline is a highly concentrated energy source, it is also relatively cheap.
Drive into a garage and the petrol pump will fill up the tank at a rate of about 1 litre per second.
One litre of petrol yields 34,000,000 joules of energy when it is burnt.
A petrol pump could therfore supply energy at a rate of 34 million watts. This is an huge amount of energy,
A typical coal-fired power station might only supply at a rate of 2000MW - this is the equivalent of roughly 60 petrol pumps!
"there are, as yet, still no adequate alternatives to gasoline or diesel for road transport."
"... for road transport of individuals in a one-tonne vehicle", I think you meant to say.
Because otherwise, you know, we have these things called "legs", and later inventions like a "bicycle" or a "bus" (they can make those electric, too - with batteries, and/or overhead lines).
Oh yes, I was just keeping it to the point of compressed air car, or any other potential alternative energy private car. :-)
Can you even imagine a compressed air powered 42 tonne delivery truck or a 'road train'?
Actually, there are around 6,000,000,000 people in the world who already don't travel much by car - if you have a car you are one of the all time lucky few, make the most of it.
I am surprised no one seems to have brought up flywheels as a more efficient way of storing rotary energy. Take a look at this article about http://en.wikipedia.org/wiki/Flywheel_energy_storage
Main points :
For both approaches, a tram or a bus is a more appropriate vehicle.
I think the real advantage of compressed air is low cost. It can very well be some limited kind of solution for third world countries.
Flywheels would be much more expensive and have certain safety issues too (albeit more manageable).
"Me, I'd rather we were rid of cars entirely, even if they were powered by sunshine, strawberries, and pretty girl's smiles."
It would be a horrible waste to use that for driving cars!
After the corn runs out.....
"Have you ever seem the results of a hot water storage tank exploding due to the failure of the temp/pressure valve and faulty thermostat." No, but I have seen fully charged scuba tanks survive intact in the trunk of a car that had been rear ended on a highway. I probably wouldn't want to repeat the experiment too often though.
When I was training to be a fireman, I had to bring my SCBA (Self-contained Breathing Apparatus) with me to the classes in either my car or the fire companies truck. When I packed the tank, I always made sure that the valve was pointing towards the front so that if it got knocked off, the tank would go out the back of the vehicle and not through me.
On one the many sites this company (MDI) publish there is a photograph showing three tanks installed under the floor. (Sorry, I haven't got the link)
I guess they have used 3 tanks for better weight distribution and to minimise the the force/noise of a rupture of any one tank.
It may also allow a tank-at-a time refill from the implied 'onboard compressor' when it is running in 'dual mode'.
Its OK Kiashu, Your physics haven't failed you and you're right the tank will be quite significant.
The true problem is the thermodynamics of compressing and expanding the air. Joules are lost in both phases. There are notes that these guys have or will consider reheating the expanding air. The big gain is in economic investment and operating off the motor fuel tax hijacking.
But the biggest potential is in Di Pietro's design. While knowing that energy input is required both to compress and reheat it would be a huge stroke of design innovation to pair Di Pietro's motors in a Stirling setup. One driven by heated gas producing the torque and the other re compressing the gas cooled by doing work. Even more efficiency can be gained because a Stirling uses constant combustion instead of intermittent combustion as in an IC engine. See the idea in more detail at http://newenergyandfuel.com/http:/newenergyandfuel/com/2007/12/12/could-...
What service station now has a compressed air supply sized to recharge an air car? The only use they currently have for compressed air is running pneumatic tools and the hose used to fill up tires. For those purposes a 150 psi 5 h.p. compressor with maybe a 50 gallon tank would be all I'd expect to see. No way would that be up to the job in terms of pressure or volume.
Sure in theory they could be installed, but as with hydrogen car proposals there is a "catch 22": The stations are not going to spend many dollars on high volume high pressure compressors if they don't have lots of customers for the air, and will enough cars be sold if there is no place other than at an "at home" recharging station to get high pressure air?
From EcoGeek's review:
Somewhere on one of MDIs many websites they clearly state they require the rollout of "high volume high pressure compressors". Sure, this is a problem but not insurmountable.
What is the cost of an 4500psi air compressor? How much will it be to install it in sufficient number of locations? There needs to be infrastructure in place otherwise people won't buy the car.
A much better approach IMO would be to install the compressor with the car, so that it can recharge from any electric outlet like an electric car.
As noted above, the car includes an onboard compressor.
If you want a quick refill, go to a service station with heavy duty equipment. If you don't mind waiting 4 hours, plug the car into the wall and do it at home.
Yes, when I saw this I smelled scam. There is no way existing compressors in gas stations can do the job. Just the power requirements of one would be respectable - 20kWh for a reasonable 10 minutes makes it to 120kW. I don't think they have the power lines to handle such loads.
I’m with you it seems to be a scam.
To provide perspective on a 300 liter air tank, it could be a 32.7 inch dia sphere or three cylinders each 12 inches in dia and 53 inches long with spherical ends.
The three cylinders would no doubt be much safer and practical.
20 HP for 2 hours at 60 MPH is 30Kwh of energy.
How much energy is required to compress 30,000 liters of air into 300 liters of air at 3000 PSI. Of course the refill supply could be stored in much larger containers at higher pressure.
Yes, it has "SCAM" written all over it.
I don't agree that the power limits are a problem, though. A filling station could have a compressor that runs all night, putting air into a series of high-pressure tanks. During the day, the tanks would be drained; the only immediate power required would be to top up the difference between the highest-pressure tank and the maximum filling pressure. This is pretty much how SCUBA tanks are filled from sets of high-pressure storage tanks.
Given that the methods are old hat, why weren't they mentioned on the site? This also yells "SCAM", because they couldn't even be bothered to refer to established practice to bolster their credibility.
There is no reason why compressed air cannot be piped to places like service stations from large central compressing stations.
Compressing air creates a lot of heat - this can be used to heat water that can be used by houses, factories and offices especially in the winter.
Clearly, the more effective one is at cooling the air while it is being compressed, the more efficient the whole operation is - the closer it is to an isothermic process. I suspect multi-stage compression is the way to go.
I don't seem to have noticed anyone pointing out that in Australia there is a lot of sunshine and heat in the summer. If the compressed air is warmed up (perhaps by passing it over a heat-exchanger on the roof), the same tankful will take you quite a bit further. Also, the exhaust from the engine can be used to cool the interior of the car most effectively!
The reason is called "frictional losses".
Good point
To say that the wind power to compressed air storage is a commercial entity is not correct. The Iowa site referenced isn't even under construction yet. The project isn't scheduled for operation until 2011.
Yes - sorry - that was a bit garbled - I meant compressed air is already in use for large scale energy storage (as per the examples in Germany and Alabama) and will be used in conjunction with wind power shortly (as per the planned developments in Iowa and Texas).