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MDI Shows New Compressed Air Vehicle at NYIAS; Plans Larger Vehicle for US Market in 2010

The new MDI economy/utility car at the New York show.

MDI (Moteur Developpment International) Group, the French developer of compressed air vehicles, and Zero Pollution Motors (ZPM), MDI’s North American representative, is showcasing MDI’s newest compressed air vehicle—an economy/utility car—at this year’s New York International Auto Show (NYIAS). The vehicle made its debut at the Progressive Automotive X PRIZE (AXP) (earlier post) booth at the show. ZPM and MDI have entered a team to compete for the Progressive Automotive X PRIZE.

The new MDI economy/utility car is powered by the Compressed Air Engine (CAE) invented by Guy Negre, CEO and founder of MDI, and is one in a series of vehicles to be developed by MDI for production in various markets throughout the world. In 2007, MDI signed an agreement with Tata Motors for the application of CAE technology in India. (Earlier post.)

ZPM plans to introduce a 6-seat, 4-door family-size version of the compressed air vehicle to the US market in 2010. The ZPM model will achieve more than 100 MPGe and more than 90 mph, have zero to low C02 emissions and cost around $18,000.

MDI and ZPM will enter two vehicles in the Progressive Automotive X Prize competition: the US production 6-seat, 4-door family-size model will compete in the Mainstream Class; and the 2-door, 3-seat economy/utility model on display at NYIAS will compete in the Alternative Class. The economy/utility model will be produced by MDI for sale in France and elsewhere in 2009 at a price of beginning at around $5,000-$6,000 for the basic model.

The core of MDI’s work is a piston engine powered by the expansion of electronically injected compressed air. MDI has developed two versions: a single fuel engine that relies solely upon compressed air, designed for urban areas only; and a dual-fuel version that uses compressed air and a combustible fuel (petroleum-based or biofuel). When running under 35 mph, the engine runs solely on compressed air. At speeds greater than 35mph, the engine uses small amounts of fuel to heat air inside a heating chamber called the Compressed Air Multiplier (CAM) as it enters the engine.

The MDI Engines consist of an active chamber and are made up of modules of two opposing cylinders. A proprietary connection rod allows the retention of the piston at top dead center during 70° of crankshaft rotation—providing enough time to establish the required pressure in the cylinder. These modules can be coupled to make groups of 4 or 6 cylinders for a range of uses from 4 to 75 hp.

The 6-passenger car targeted for the US—formerly known as the CityCat—will use a six-cylinder version of the Compressed Air Engine that is Compressed Air Multiplier (CAM) enabled and will deliver an estimated 75 hp (56 kW). MDI projects that the vehicle will have a top speed of 96 mph, and offer fuel consumption of 106 mpg US (2.2L/100km) when driving at speeds above 35 mph. This will result in greenhouse gas emissions of approximately 40 gCO2/km. With an 8 gallon fuel tank, the car will have a range of 848 miles, according to MDI.

A tank holds 3,200 ft3 of compressed air at 4,500 psi (310 bar). An on-board plug-in compressor generates 812 ft3 per hour.


Healthy Breaze

So...below 35 mph it's an electric car which takes 4 hours to recharge...with how much all-electric (all compressed air) range?

The French version they showed on YouTube a year ago was hardly more than a kit car...very stripped down structure with no indication of safety structures.

Even in range extender mode, it still seems as though it needs the compressed air, so refill time is a concern. Are they proposing compressed air quickfill stations that would have large tanks of prepressurized air at the ready? Say, I remember seeing a kid at the gas station inflate his bicycle tires so much that they popped...oh well...they have worked hard at this, and addressed many concerns to date. I wonder what the well-to-wheels efficiency is of compressed air (storing electric power)?


If it works, even less efficiently than todays EVs, its still a better choice in my opinion, since there's no chemical batteries needed and the tank will probably last longer than the batteries. The rest of the car I don't know.


It seems that the transmission is a CVT.
I think the NuVinci CVT would be good for the light versions of these vehicles, as it looks that the NuVinci transmissions are efficient.

The Scoot

The one thing I am concerned about is traffic safety. A pressure vessel is not something to screw around with. Sure, gas burns, batteries have caustic chemicals, hydrogen burns...

Have any of you seen a pressure vessel catastrophically fail?

That being said, if it passes NHTSA safety tests, sign me up for one of the first models...

Paul F. Dietz

Are they proposing compressed air quickfill stations that would have large tanks of prepressurized air at the ready?

Yes, I believe so.


So those MPGe values are not including the energy taken to compress the air? That's what I'm most interested in. There's an 8-gallon tank for hydrocarbon fuel, but how big is the air tank? 3200 ft^3 at 310 bar comes out to 77 gallons, which is big. Maybe they meant 320 ft^3 ?

320 ft^3 at that pressure seems to have about 2.5 MJ of energy. A gallon of gasoline is typically quoted as 121 or 131 MJ. Of course, considering that a gasoline engine is only running around 25% efficiency, we can say that there's effectively only 30-33 MJ per gallon of gasoline. So on one "gallon", you'd only expect to go 1/12th the distance for a similar vehicle.

Now I get to the wild inconsistency that the ZPM website says the vehicle's weight is 1874 lbs, while the MDI site says 320 kg (705 lbs). Well, anyway, a Honda Insight is around 1880 lbs and gets around 60 mpg. A similar air car might do about 4.75 miles per compressed gallon, or around 38 miles on an 8-gallon tank. I can't say what would happen when you cut the weight in half or more. It'd certainly be better. How much is hard to say.

Wired had an article about MDI in 2003 where they mentioned the only known road test of the vehicle ended at 4.5 miles.


Er, sheesh, ~8 compressed gallons has an energy of 2.5 MJ. So, yeah, you can double the size of the tank and maybe go 10 miles, but it looks like that's about as far as this technology is going to get.

Harvey D

The scoot:

What would be the (security) weighted difference between (Air), (CNG) or (Hydrogen), compressed at about the same pressure level.

Compressed air seems to be as clean an energy source as one can get, next to 'clean' electricity stored in capacitors (without the chemical batteries). Wonder how noisy is the on-board air compressor.. neigbours.. or yourself if this is parked in your garage? Getting a very quick charge from a large high pressure tank nearby may be a better idea.

This technology may offer an worthwhile alternative to PHEVs. It would be interesting to see an in-depth comparision.

Tata is supposed to have a few versions on the road by 2010.


Have you ever used an air tool (grinder for example), they are very sensitive to pressure falls and have an extremely low efficiency when compared with electric tools.
I think that the numbers from MDI aren´t realistics.


Air tools don't use sophisticated air motors. They are designed for a world where compressed air is "free". You can't compare them to this vehicle.


So what's the deal here? Is this vehicle capable of 106mpg or not?


There's an 8-gallon tank for hydrocarbon fuel, but how big is the air tank? 3200 ft^3 at 310 bar comes out to 77 gallons, which is big. Maybe they meant 320 ft^3 ?

320 ft^3 at that pressure seems to have about 2.5 MJ of energy.

The Tesla Motors Roadster has a battery capacity of about 50 kWh or 180 MJ. And an electric motor is still more efficient than a pneumatic motor...

John Taylor

This is an updated version of the steam engine, with compressed air for steam.
A nice feature in the planning stage was using the frame as a storage tank for air.

I have not seen convincing evidence of higher fuel efficiency, or sufficient range, but it could be recharged with commercially available nitrogen in a pinch. ...

... and it is mostly pollution free...


This will never be a success as a car. You cannot store enough energy in compressed air. They might have a chance using them for material handling. For instance in-doors and/or in places with explosion risks.


3200 cubic feet !!!!!

That's the size of a shipping container! (10ft x 10ft x 32ft = 3200 Ft^3)

Does anyone know what they really ment?


Maybe 32 ft^3? 3ft x 3ft x 3.55ft=32 ft^3. Still not sure there is anywhere on a small vehicle to locate even that. 3.2 ft^3 would be about 1.5ft x 1.5ft x 1.4ft. Of course it wouldn't necbe square - but just trying to get an idea what the real number is.


I saw a story on this car and it had several compressed air tanks under the body inside the frame well protected. The story got carried away and mentioned the air powered generator and air compressor that they make. It implied that you could use compressed air to generate electricity to make compressed air on board, which implied free fuel which is non sense. I was amazed that the editor let that one pass on a supposedly scientific program.


The air tanks are carbon fiber they won't blow up like a mental tank, instead just rip or split open if there is a failure.


Earlier articles mentioned that the onboard compressor is used only when your refill at home.

Service stations would have larger compressors and storage tanks, so they can refill your car in a couple of minutes. The station pre-compresses air in its own tank, then it transfers compressed air to the tank of the vehicle.
So refill time is not really an issue after the service stations gear up which shouldn't be very costly (compressor technology is very old).

All in all this is a pretty good temporary solution until batteries reach real maturity and low cost. I hope it succeeds.


shane, I think they mean 3200 cubic feet before compression... that's about 300 liters tank volume.


Thanks Francois,

So, if I did the conversions right, a 300 liter tank, is 10.6 ft^3. This might be approx. 2 ft x 2 ft x 2.8ft. I can imagine such a volume fitting on that car. Still, the obvious question is what is it's "air only" range? x miles at a sustained 30 mph would be nice to know.


They use a quasi isotherme expansion to get better mileage, in fact there is 3 stage of expansion with reheating (at ambient) in bewteen to improve the efficiency, in fact you kind of extract enegy from the ambant air that you have lost during the compression. In theory isotherme compression / expansion is 100% efficient but in practice you can't be perfectly isotherm. I think they are about 50% efficient in this car. The problem is that the energy stored is quite limited even using 100Gallons of compressed air at 500bars so the car is extremly lightweight, the engine is very noisy and amplified by the light sheet that forms the outershell of the car. They have been working almost 20 years on this and still no car on the road...

Roger Pham

For an equivalent volume and pressure, compressed Hydrogen contains 20x the energy of compressed air. And car makers are struggling to get enough range out of Hydrogen car while still having enough internal space for passenger and luggage. So, for the Honda FCX Clarity (Hydrogen FCV) with a range of 270 miles at 60% tank-to-wheel efficiency, if compressed air is used at 70% efficiency, will have but a 14-mile range between fill-up of compressed air. Probably a lot less, since the FCX Clarity has an H2 adsorbent matrix in its H2 fuel tank in order to pack a lot more H2 molecules at 350 bars of pressure, than an air tank having the same size and pressure.

Good Luck, AirCAr, and Tata motor.
TTFN! (ta ta for now!)


CNG seems to a relatively new concept in the US, whereas in India it is a well-entrenched concept. Most taxis where i live, run on CNG or LPG. The quality of air in Delhi has been considerable enhanced in the past some years by buses and auto-rickshaws turning to CNG. Electric vehicles are also being main streamed here in a big way.


I'm trying to keep an open mind on the MDI, but....

It seems to use similar tankage as with hydrogen/CNG, but a lot more of them. The video had two huge cylindrical tanks in the frame. I can't believe they aren't really expensive, because they are carbon fiber. On the other hand, they are only holding about 4000 psi instead of 10,000 psi for hydrogen. (The 10,000 psi tanks are ridiculously expensive...)

I also noticed they are also very loud when running, though maybe that could be improved over time.

4 hr recharge time is really not too bad, but faster recharge requires significant infrastructure.

I still see a plug-in hybrid concept as a better overall solution, as the gasoline option provides range, rapid refuel, and extant infrastructure.

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