Cars running on compressed air?

It looks like an Indian car company is trying to commercialize a car that uses a compressed air engine. They claim:

  • Costs about 1.50 Euros ($2.20) to refill the compressed air tank.
  • Can run for 125 miles before refueling.
  • Can reach speeds up to 68 MPH.

Looks pretty darn impressive.

What psi do you think would be needed in the tank to reach these levels of performance? Why isn’t this getting more hype?

From Scitizen

Credits to Dr. Muller and Greg Muller:

Safety Issues:

A 79 gallon tank at 4,400 psi. This is a LOT of potential energy to have underneath you in a high speed collision. What does the company say to skeptics?

Compressed air tanks have already been tested safe by one of our partners EADS(AIRBUS). This company’s reputation in the aeronautical field is indisputable, and they have been proven in a thorough way the reliability of our tanks. What’s more, the compressed air does not present any risk of explosion. Countless tests have been carried out in the most extreme conditions (gun shoots, resistance to fire…) to guarantee passenger safety in every possible condition. The high pressure tanks have been developed using a similar technology as those used in natural gas vehicles and by firefighters. All are produced with carbon fiber over plastic.
The tanks that MDI puts in its vehicles are similar to those already in use in natural gas busses in Germany and also other countries.”

Believe them? I’ll let you decide for yourself. It should be noted that this car has not passed US safety standards, only European. Not sure if there is much of a difference.

Maintaining Peak Power:

A question they don’t seem to answer on their website is how the same amount of power is available when the tank is full as compared to almost empty. Since the tank’s volume is constant, the pressure will lower as the air is used in the engine. This lower pressure would result in decreased engine torque. Any ideas as to how they might be working aroung this issue?

NEW (2/13): The Hydristor


This design is being developed for both new installation in cars and retrofits. Instead of a conventional hybrid, which regenerates energy from braking into a battery, this system would store the shaft power of braking as compressed air. The device, i would assume, is essentially a compresser that can work at any load level. This design also has appeal for the grid: if compressed air ever became a realistic way of transporting energy, this device would act as the transformer to convert to appropriate power levels.

As this article suggests, if wind turbines could store their energy in large compressed air tanks instead of being converted directly into electricity, it would help mitigate the problem of inconsistent power from wind.




11 Responses

  1. How Stuff Works has a short article on Air Cars that is nice enough to contain some hard stats:
    They say the tank is 79 gallons at 4,400 psi, which sounds astoundingly dangerous. Mythbusters recently showed what a 40 gallon tank of water at 350 psi would do when compromised:

    I’m not sure I want to be in a high speed accident while something with 20 times as much stored energy is four feet from my legs. And to top it off, they said the tank is made out of carbon/glass fiber. Safe!

  2. Compressed air is a longtime energy storage favorite – but the devil is usually in the details. I would worry about leaks – at 4000 psi, the engineering would have to be pretty spectacular. Also, the power would go down as the pressure dropped.

  3. While the gas is contained at 4400 psi in a constant volume tank, this does not mean that the engine will be using all 4400 psi. The only way I see that working is if they design the engine to utilize the air at say 500 psi (I’m just picking a number for this). Then, you utilize a regulator to step the 4400 psi gas down to an output pressure of 500 psi. Ideally, the engine could run at full capacity until the tank drops below 500 psi. Such a regulator is used in all paintball and airsoft guns. The tanks store the gas at at least 3000 psi but shoot at only a few hundred or so. I’m not sure if the technology can scale without major power losses though.

    As for safety, paintball guns also use carbon fiber tanks. They regularly have to be tested for hydrostatic safety and some fail. Those that fail explode nearly completely. Until someone can point towards a way of having a rupture in a 4400 psi tank that doesn’t also rip apart the rest of the tank, I will be a bit wary of this system.

  4. The tank of 79 gallons pressurized at 4400 psi does not contain enough potential energy to move the vehicle the claimed range of 125 miles. The calculations to determine the energy content of a pressurized air tank is not rocket science, just high school science.

    In a test of a prototype the car traveled 7.22 km, less than 5 miles. But, armed with that performance, they claim that translates into a range of 125 miles.

    It seems these “inventors” are making effective use of a press and media that love a “sensational” story. The media publish the claimed performance figures and range of the vehicles as FACT, without question.(Sells magazines keeps eyes on the TV)

    Venture capital funds are always looking for promising ways to invest in new technology, if this idea was worthwhile, the venture capital funds would be offering BILLIONS of dollars to help the “inventors” get the factories producing cars already.
    The “inventors” have been touting this idea for over 10 years, the car will always be available “next” year.

  5. The test data that Avaqadro refers to is not on the MDI website, but it can be found in the internet archives:

    7.22km actual run of the prototype, and then extrapolate improvement after improvement after improvement to turn that into 191.1km or 242.2km.

    This is on an older model, but I suspect that all of the range numbers for later models are based upon this same ancient test.

    If ANYBODY has ANY real test data more recent than this, I’d be very interested in seeing it.


    As for the original article about Tata Motors. When first announced in mid-2007, production was supposed to be in July 2008. In August of 2008 the president of the passenger motors division of Tata announced that the program was still in the early development phase and production was nowhere in the near future.

    This is in keeping with the history of claims of mass production “soon” that never happen. The oldest false start of MDI that I have found was a BBC article in 2000 about 6,000 vehicles to be produced in South Africa by 2002 or 2003. As best I can tell, this never happened. Does anybody know the status of that project ???

    Or the project where the Mexican goverment was supposed to have bought few 10,000’s of air-powered taxis? It just seems to have quietly disappeared. Does anybody know if even a single prototype was built and delivered to Mexico??

  6. I noticed that this is not the first time you mention the topic. Why have you decided to write about it again?

  7. A pleasure to come to your site. Thnks very much!

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  9. Some very interesting and insightful thoughts. I like this.^_^ because I have a blog about used car too.

  10. @Markus I get your drift on where you were going there. I often think of my past and use it as a means to analyze where I am and where I want to get to. Where I struggel is balancing it all out. How do you guys balance things out?

  11. How come you do not have your website viewable in mobile format? Can not see anything in my netbook.

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