The Air Car Can Blow You Away
If you inflate a balloon and place it on a little toy car frame and then release it, it will race across the room until the balloon deflates. That is essentially the idea of engineer Guy Negre of MDI in . Popular Science magazine reports he is working with an Indian company to put about 6000 Air Cars on Indian streets by August 2008.
In case you've missed the previous stories (see below), Mr. Negre is using a piston-type engine to extract the stored energy in the compressed air to drive the wheels. This makes elegant sense. Why do we combust air with fuel in an engine? To get high pressure, of course! Compressed air at 4350 psi is powerful! And it takes energy to raise air to that pressure level with is actually 290 bar (290 times higher) than atmospheric pressure. Stored gas pressure is like stored energy in a battery. You put it in at one time, and you take it out later. Gasoline and diesel engines put energy in (the fuel) and take it out at the same time.
Compressing air to 290 bar is a relatively straightforward task. Take a reciprocal compressor, power it up, fill the Air Car's tanks in a few minutes, and then drive away. That takes energy, probably electric energy, to get that done. Petroleum use can be avoided but electric use is still needed. The car will even come with it's own on-board compressor. Refilling that way should take about 4 hours.
The range of the vehicle is said to be 125 miles and it has a top speed of 68 mph. I haven't gone through the thermodynamics of the full process but I gotta admit this is a pretty nifty way of circumventing petroleum use. If the compressor is green-powered (solar, water, wind, etc.), the Air Car will be too. And vice versa.
Related:
- A new agreement between Tata Motors and MDI bring the air-car closer to reality
- India's Tata Motors and France's MDI sign agreement to build compressed air-powered cars
- Old video of air-powered car making the rounds at YouTube
[Source: Popular Science, MDI]
Reader Comments (Page 1 of 2)
Devin 4:23PM (2/01/2008)
In response to "2006 Honda FCX" being 50% efficient, that's extremely high considering that fuel cell vehicles are between 29-54%. Although, Electric Vehicles with NiMH batteries (100% recyclable) would achieve 68% efficiency with even the cheapest motor, charge controller, voltage controller. Spend some more money and you could get that NiMH vehicle up to 80% efficient. So:
The air car needs to pressurize the air PERIOD. All three in fact: Air Car, Fuel Cell, Battery EV all require electricity.
The question is: Which one is more efficient from the plug to the drive train? (assuming all three have the same efficiencies from motor to wheels)
Reply
alpan 3:13AM (3/29/2008)
It's more likely that the air tank will have to be subdivided into smaller compartments (like the reverse concept of a submarine when a torpedo hits). In that way, it seems like this could indeed be a viable concept. But don't hold your breath waiting for the gasoline engine to go away: The lost tax revenues alone make this car an impossibility for the US market.
Reply
Charlie 10:19PM (11/25/2008)
OK. It's well past August 2008. Where are the 6,000 air cars that were supposed to be on Indian streets? The last thing I heard from Tata Motors was from the President of the passenger car division saying that the MDI air car technology isn't yet ready for production anytime in the near future.
Where is the MDI e.Volution car that was said to be ready for production in 2000, with predictions of production in France by MDI in 2000, by Zero Pollution Motors in South Africa in 2002 and by MDI franchisees in Mexico in 2003? Where are the OneCat and other "Cat" cars that were going to go into production in 2005?
It seems that all of these have just disappeared into a collective memory hole and have been replaced by the latest announcements by MDI on the new series, the AirPod, which is due to be manufactured "next year".
It seems like all MDI and Zero Pollution Motors need to do to get lots of glowing press is to announce yet another model of car with a bunch of unsupported, untested, unverified specifications and with production "next year".
Reply
Scatter 12:08PM (5/29/2007)
The link is going straight to the Air Car website. The PM article is here:
http://www.popularmechanics.com/automotive/new_cars/4217016.html
If the price and range are correct then it looks like we have a very useful, very clean car. A bit more range and the Automotive X Prize will be within their grasp.
Reply
Tush 12:11PM (5/29/2007)
I'm not sure what the benefits of this are...
It seems like this air car has similar energy production to an electric car. Actually, there must be energy lost in compressing air, why not skip that step and just store it in batteries?
Reply
Scatter 12:22PM (5/29/2007)
Becuase it's cheap and for the price appears to have better range. There are losses involved in charging batteries after all. Plus the air can be compressed using a local wind or hydro powered mechanical compressor. The test will be what sort of emissions are generated by an ICE/electric compressor.
Reply
Kardax 12:29PM (5/29/2007)
A cool idea, but ownership of an air car needs to be price-competitive with other alternative fuels if it is to succeed.
No one in the air car business likes to talk about this, it seems...
Reply
Tim 12:46PM (5/29/2007)
Question: What's the least expensive, least complicated, easiest to implement and safest way to store energy... (a) a tank of compressed air, (b) a tank of compressed hydrogen with a fuel cell or (c) a L-ion battery with it's control system and related electronics? Some of the big thinkers out there may have to ponder this brain teaser. That's OK. Take you time as we send more oil money to Al Qaeda...
Reply
Jenny 12:52PM (5/29/2007)
This will definitely become a cheap solution since it is produced in India and 2008 is not far away. We can experience this in the near future.
Jenny
http://www.spaml.com
Reply
Tony Belding 1:18PM (5/29/2007)
I believe the efficiency of compressing air and then recovering useful energy from it is going to be considerably lower than the efficiency of storage batteries and electric motors. It could be cheaper to produce. . . But large carbon-fiber tanks capable of storing high-pressure air are more expensive than you might imagine. Energy density is also a problem. There are also safety concerns that must be addressed.
Promoters of these cars like to start their sales pitch by saying "air is free!" and then hope the discussion never goes any further than that.
Reply
Scatter 3:00PM (5/29/2007)
I don't think they're hiding anything. The website is pretty open and discusses the design in reasonable detail. Any safety issues can be overcome with good engineering. Energy density doesn't appear to be a problem assuming the performance figures are correct. Let's not get too cynical and jaded before they've even produced it eh? :)
For me it's a pretty simple situation: EVs, while promising lots, are yet to deliver on cost and performance (both range and battery life) and it will likely take a long time until they do. In the meantime there is a very large gap in the market for a good value, clean car and if they manage to keep the cost and range on target it's looking like this car could fill that gap. I am going to follow this company closely and will seriously consider buying one.
Reply
Greg G 5:39PM (5/29/2007)
There is another fine benefit:
If you put the fill valve at the back of the car and fully open it with a button conspicuously labeled "rocket booster" then you can enjoy unsurpassed acceleration and be able to jump over unfinished bridges, small houses, etc.
Reply
Tim Butterworth 6:51PM (5/29/2007)
@ Tush: The advantages are weight savings (an electric conversion generally adds from 200-600 lbs to the original weight of the ICE car,) simplicity, and safety. This car could be made to be almost inflammable. Also, hp density in this engines design is very high - a 10 hp motor could fit in the palm of my hand. The only real concern in bringing it to the US is highway regulations. In other countries, people can drive however they want, so long as they dont endanger others. Here in the US, we have freedom from fear, freedom of religion, freedom from want, and freedom of speech, but not the freedom to die. hypocrites and corrupt. lets hope Obama endorses a few more options like this for transportation.
Reply
Joseph 9:38PM (5/29/2007)
@ Tim Butterworth
"hp density in this engines design is very high - a 10 hp motor could fit in the palm of my hand."
Whoa, whoa, whoa, just how big is the palm of your hand?
Reply
UH2L 11:13PM (5/29/2007)
All good discussion above. What we haven't mentioned yet is that compressed air tanks are probably much more environmentally friendly than batteries, in manufacturing and especially from a disposal perspective.
Atul
http://www.thingsivenoticed.com
Reply
ccweems 6:33AM (5/30/2007)
This is all old news (since 1991). The concept is flawed, they have yet to produce 1 car that meets specs. If you dive into the background and other attempts to do the same thing you come up with the realization that compressing and expanding air includes some undeniable physics which limits performance. There is a reason why MDI has not succeeded apart from sporadic infusions of cash by well meaning investors: it doesn't work. Go browse around the website. Periodically they raise interest which is always presented as news breaking but when they have to present demo cars they fall flat and on many facets.
Can I talk to about Herbalife?
http://www.theaircar.com/
Reply
Travis 6:42AM (5/30/2007)
Yeah it'll blow you away with how gay that car is. Fantastic.
Reply
Nils 7:10AM (5/30/2007)
If I remember well, the thermodynamic efficiency of compressing and expanding air to do work is bout 0,4. That's bad, very bad.
Reply
Scatter 10:13AM (5/30/2007)
Seems a bit odd that one of the world's largest car manufacturers with a revenue of billions is licencing the technology then. Clearly they should read more blog postings so that they can find out the truth...
Reply
Roger Pham 2:11AM (6/04/2007)
Folks, please don't be fooled by the aircar.con hype! Open your physics book and do the math! Or please considering the following:
According to the gas law, the energy required to compress a given molecules of H2 and air is quite comparable. It takes ~9% of the heating value of H2 to compress H2 to 5000 psi using near-isothermal commercial multi-stage compressor. When you discharge these compressed gases by powering the airmotor without combustion, you'll get back 7% of the heating value of H2, given the fact that you do not quite obtain isothermal expansion at even low cruise speed of a car at 30mph, according to the aircar setup. Assuming 70% mechanical efficiency of the airmotor engine/transmission, you'll only obtain .70 x .07 =0.049, or ~5% of the heating value of H2.
Now, the 2006 Honda FCX fuelcell car has an overall efficiency of 50%, 3.75kg of H2 stored in tank of 156-liter size, and the car can travel 210 miles. The overall weight should be comparable between the aircar and the Honda FCX, because air is much heavier than H2. The energy in the heating value of the 3.75kg of H2 in the FCX should be able to get the FCX to 420 mi-range if the FCX can operate at 100% efficiency. Now, since an equivalent aircar can utilize only 5% of the energy inherent in the compressed hydrogen since it only uses the energy of compression of the gas, and not the energy of combustion, the aircar can only travel 420 miles x 0.05%= 21 miles.
How heavy is the air storage tank? At ~4% gravimetric efficiency of H2 compressed-storage, 3.75kg should weigh about 90kg for the tank. Adding the weight of compressed air, which is ~15 times heavier than H2, or 3.75 x 15= 56kg. 56kg + 90kg for the tank weight will give you 146kg, or 321 lbs. Assuming 200wh/mi x 21 miles= 4200 wh energy stored / .7 efficiency= 6000wh total battery energy equivalent. 6000wh/146kg= 41wh/kg. Ain't too bad, since NiMh battery can store ~65wh/kg, whereas 123Lithium ~120wh/kg. But look at the huge volume required! 156 liters or 41 gallons. If one double this volume and thus having no trunk space whatsoever, you'll get a pitiful~40-mi range for a car having no trunk space left for luggage.
This is Ok for an urban car stuck in traffic at 20mph, in which its range can get to 60-80 miles given the fact that at slow speed, more isothermal expansion is possible using ambient heat, and in hot tropical climate like India, you'll get free airconditioning due to the low temperature of discharged air. The aircar is definitely not practical for the USA or Europe!
Reply