Tata Motors’ Air Car: Which Way Does the Wind Blow?

It seems like every few months, we get wind of another vehicle that is supposed to be powered by compressed air. The Mini Cat Air Car, from India-based Tata Motors, seems almost too good to be true. Tata Motors is India’s largest automobile company. It is the leader in commercial vehicles, and among the top three in passenger vehicles.

Designed by an ex-IndyCar™ engineer, the Mini Cat utilizes compressed air to move its motors’ pistons, claims zero tailpipe emissions, and an extremely low cost to run. Is it the real deal, or a lot of hot air?

Compressed-air has been used to power a wide variety of vehicles since the 1800s with only limited success, due to inherent inefficiencies. The concept found some limited success in powering locomotives, mostly used for mining, where a combustion-free energy source was desirable. Ultimately, even these were replaced by more efficient electric motors.

Several modern companies have attempted to produce a working compressed-air powered car, but none have yet to reach the consumer market.

Tata Motors' compressed air engineEnergine Corporation, of Korea, claimed that it was going to deliver a hybrid compressed-air/electric car, only to see its CEO arrested for making exaggerated claims.

K’Airmobiles, a French company, were another compressed air concept, but it never saw the light of day. The company was unable to procure the necessary funding, and the engineers who worked on the project, ultimately admitted that the inherent efficiency and low-running-temperature problems made the project unfeasible.

In 2010, Honda showed off the Honda Air concept car, a 1,000-pound, 4-passenger car, made out of composite materials. (While the concept sounds good, in theory, I would hazard a guess that the high price of the composite materials used in this car would make it unable to compete with other alternatively-fueld vehicles.)

The TaTa Air Car concept engine was developed by Motor Development International (“MDI”), of France, with the backing of Tata. (This version of a compressed air engine has been in development for over 20 years.) Zero Pollution Motors holds a license to produce the cars in the U.S. market.

However, this version of an air-powered car has also been beset with problems.

In 2008, Popular Mechanics wrote, “Zero Pollution Motors confirmed to PopularMechanics.com on Thursday that it expects to produce the world’s first air-powered car for the United States by late 2009 or early 2010.”

Tata Motors' compressed-air powered car.Although there are several blogs, and news outlets, which still refer to Zero Pollution Motors as the holder of the U.S. license to produce MDI’s Air Cars, I was unable to uncover any evidence that the company is still in existence, at least in any substantial form. (For example, the company’s website, zeropollutionmotors.us, has a suspended domain name.)

In 2009, Tata Motors’ vice-president (engineering systems) S. Ravishankar told DNA Money the project is facing difficulties in terms of vehicle range and cooling. Ravishankar said, “Air is not a fuel, it is just an energy carrier. So a tank full of air does not have the same energy as a tank full of CNG. Any vehicle using only compressed air to run would face problems of range.”

The article continues: “Ravishankar…went on to say that excessively low engine temperature is another problem, in a vehicle using only compressed gas as fuel.”

In April of this year, InAutoNews.com explained that the cars, intended for the U.S. market, would not be entirely emissions-free, because a small gasoline engine was required, to allow the car to run at city speeds. (Perhaps this was the reason, for the long delay, in bringing the air car to market? Perhaps the designers were attempting to figure out a way to make the One Cat run on compressed air, only?)

In December of 2009, UC Berkeley, ICF International and Stanford experts had this to say about the feasibility of compressed air versus chemical fuels, as an energy storage medium: “The study concluded that even under highly optimistic assumptions the compressed air car is less efficient than a battery electric vehicle and produces more greenhouse gas emissions than a conventional gas powered car with a coal intensive power mix. It did state however, that a pneumatic combustion hybrid is feasible and inexpensive and could compete with hybrid electric vehicles.

So, it would appear that the jury is not entirely out on the feasibility of a compressed air powered car, but it certainly does not look good for the Tata/MDI version.

But let’s assume that the Mini Cat Air Car really does live up to the claims of the manufacturer. Just how environmentally-friendly is a compressed air car, anyway?

In 2009, that’s exactly what Popular Mechanics endeavored to find out. They compared the Zero Pollution Motors AirPod (an extremely strange-looking precursor to the Mini Cat), to electric, gas, hybrid and diesel. The numbers include the CO2 produced, by the generation of any required electricity. The results were interesting:

  • Zero Pollution Motors AirPod: “24.014 pounds CO2 for 100 miles”
  • Tesla Roadster: “32.98 pounds of CO2 for 100 miles”
  • 2010 Toyota Prius: “39.192 pound of CO2 for 100 miles”
  • 2009 Honda Civic (non-hybrid): “64.67 pounds of CO2 for 100 miles”
  • 2009 VW Jetta TDI Diesel: “62.5 pound of CO2 for 100 miles”

Popular Mechanics’ conclusion? “The AirPod is CO2-light, even for a tiny three-seater (although we wonder if the mileage goes down with three people onboard, which effectively doubles the vehicle’s weight). But zero pollution? Not so much.”

So, from a strictly empirical analysis, it would appear that air cars (if they were feasible) would have a bit of an edge where pollution is concerned. Of course, air cars would still not have the speeds necessary to allow them to be driven on highways.

Being an eternal optimist, I still hold out hope that Tata isn’t just “blowing smoke.” I’m not going to hold my breath, though.


Steve Puma is Director of Business Development for SABA Motors, and a sustainability writer/consultant. His work focuses (mostly) on clean transportation, including Plug-In Electric Vehicles, something he is very passionate about.

Steve holds an MBA in Sustainable Management from Presidio Graduate School and a BA in Computer Science from Rutgers University. You can learn more about Steve by reading his blog, or following his tweets.

Steve Puma is a sustainable business consultant and writer.Steve holds an MBA in Sustainable Management from Presidio Graduate School and a BA in Computer Science from Rutgers University. You can learn more about Steve by reading his blog, or following his tweets.

43 responses

  1. I love this thing as a concept… I suspect it really could have a great application as a delivery vehicle or golf cart type thing. I also wonder about popular science’s calculation – did they say what kind of power generation that was? Assuming it’s Coal is one thing, but other methods would likely turn in the AirCar’s favor!

    1. I don’t know…I think we aught to “Ask Pablo” about this one… It sounds great, but my gut tells me that something isn’t right. There’s just too many people who say that the physics don’t work out, and there is an odd lack of transparency, from the various companies involved.

      For example: there is no mention of the Air Car on Tata India’s website (try doing a search on their site). Wouldn’t you think that they would be making a big deal out of it, if it was actually going to be coming to market soon?

      The U.S. licensee doesn’t even have a website, anymore!

      Seems like somethings’ rotten in Denmark…


      1.  They don’t have a market because they haven’t made it safe yet. It is a vehicle for commercial property, not public highways. Right now it is made out of fiber glass, and did you know India lacks basic traffic controls? They don’t want to die just to have air-powered vehicles. You should be able to look beyond this. They have the capability to make it out of stronger materials and put a generator in it to make it self-generate its own air, which could potentially make it faster as well. Have some foresight, don’t let pessimism shoot down a revolution in transportation.

    2. Steve Puma, don’t bother holding your breath. This article is a hit piece to keep people in a mindset(i.e. enslaved to gas), not a solution to it. You just let Popular Mechanics keep pulling the curtain over your eyes. Meanwhile, the rest of us will actually work towards a better world where we do not need that dirty oil. If you think compressed air is so dirty just stop breathing all together. Thanks.

  2. I don’t understand how these CO2 numbers add up. It’s fairly easy to show from a college sophomore level class in Thermodynamics that it takes 7 times the energy to compress air than physical work you can get out of compressed air.

    I’ve worked as an industrial energy consultant and when trying to reduce a manufactures energy bill one of the easiest things to look at is how to reduce their compressed air use or make their compressed air system more efficient. This is because it is actually quite expensive to compress air.

    Seems like a battery driven electric car would produce a great deal less CO2. Since charging a battery is about 80% efficient and an electric motor is about 80% efficient. Most industrial air compressors are driven by electric motors, so how can compressed air produce less CO2 then a battery driven car?

  3. Excellent overview and analysis, Steve.

    I think that the main issue lies in, as you quote: “Air is not a fuel, it is just an energy carrier”. To extend that reasoning: I think it only carries energy because it has been compressed and where do you go beyond current compression technology while still having a viable storage inside of a vehicle?

    I drive on compressed (@ 3,600 psi) natural gas. The tank takes up most of my trunk space, and I get a range of just over 200 miles with it. And that is with a fuel that has an energy density (Wikipedia) of 9 MJ/L. Compressed air at 4,350 psi has an energy density of 0.2 MJ/L.

    In practice, I can squeeze about 6+ gasoline-gallon-equivalents into my tank, which translates roughly into 800 MJ of embodied energy to drive with. The volume of the tank is about 100 Liters, which gives you about 20 MJ of potential energy in terms of compressed air.

    800 MJ vs. 20 MJ seems to be a very big gap to bridge for a non-fuel. Either my back-of-envelop calculations are off, or somebody needs to explain where the additional propulsion energy will come from to make this technology viable. I’d think you would want at least 200 – 400 MJ for practical applications, assuming a lightweight vehicle.

  4. We forget that when air is compressed it generates heat, so it has to be cooled in order to squash as much as possible into the storage vessel. Theres your first loss of energy.

    Further, it is not practically possible to expand the air completely in the engine. In an IC engine or even a steam engine, the exhaust is opened (at about 50psi) with about 50% of the available energy un-utilised.

    It would be good if a schooled reader who has the exact calulations on compressed air to reply so as to close the topic.

  5. Air as energy storage stores just 14wh/kg. This is from the weight of the air and includes nothing for the container.
    As you may know this is less than half as good as a lead acid battery.
    Greater pressure in the air tank adds more weight so the figure doesn’t change.
    Be indeed skeptical of an air car.
    Though trams, buses, and drag cars all don’t need range – but would still be impractical until efficiency problems are solved.

  6. Just look at wikipedia articles, and more complete, at the related wiki discussions, on english, french and german wiki (aircar, mdi, etc).There you will also find the thermodynamic calculations.
    In a nutshell: probably just enough energy for a 10 mile ride on a flat surface…(300l @300 bars)
    And, considering the history of MDI : lots of people are more than convinced that this is just a money-making hoax

  7. Surely using compressed air as an energy storage medium is feasible if the heat produced at compression is used for something like space or water heating, and then the heat gathering capacity of decompressing air is used with the waste heat of a small IC/or fuel cell motor.
    Isn’t this what MDI was working on?

  8. This is interesting technology, just as fuel cells and electric vehicles are interesting. They all have something to offer. Tesla has brought a lot of hope and excitement with their electric while Nissan has only done a so so job. G.M. seems to have given up on Fuel cell technology and I haven’t heard much lately about the Honda project. Air powered cars may be a pipedream for the time being, but it’s an interesting concept that I would like to see explored much further.

  9. This story of MDI and aircars has been going on for more than 15 years now. Always the same promises concerning production start (“production will start next year”) and range (“around 150 to 200 km”).
    Interestingly enough EVERY partner that ever worked together with MDI stopped their partnership. The last one of this impressing list of ex-partners is Catecar in Switzerland (stopped in march 2011).
    As other readers stated in their letters, the energy to compress air and the outcome in an compressed air engine is simply a disaster in terms of efficiency. I worked in industry long enough, I am an engineer and I can tell you without any doubt whatsoever that compressed air is the most expensive energy carrier that is (due to its inefficient production, this being due to thermodynamic laws more than 100 years old).

    The only REAL question in all this is: how stupid are the engineers at Tata?!?

    1. Maurice, I like your comment “stuck in the middle”. But being also an engineerRemember about 200 years ago Buminogori said to Buminogoro ” what = °î° %^^[m€^§ydd>> fucking wheel@|^^§vv=???”. And you know what happened. :-))

  10. we face with allat of praploms in afghanistan for example air pulution high price of fuel derty weather.so iam be the first porsan to buy that car and also import to afghanistan

  11. I have built a hybrid hydraulic car my self and folks are always sure to mention the aspect of the compressed inert gas in the accumulators that is much the same as in this car.
    In as much as I am building it my self, I approach it like a hobby and work on it from time to time. It is kind of assuring to me that this is not an issue. I have always considered all kinds of power sources have their drawbacks. What with the possible fire with fuel tanks, oxidized heavy metals from electric cars etc. Even horses have their issues, only I guess I kind of prefer them to most others.

    1. Ed, don’t know if you monitor replies to your posts, but if so I’d like to correspond with someone like you. I have been searching the internet for people who are building – or have built – a hybrid hydraulic. It’s something I have been wanting to do for a good many years now but have been unable to for a variety of reasons. It might be out of the realm of possibility for me now, but I still would like to talk shop with those who have tried and done it. If you agree, let’s see if we can figure out something. My name is Neil Larkins and I’m on facebook for a start. (In searching for you on facebook, I see that there are a whole bunch of “Ed Watts.” So let me know if you want. Thanks.

      1. Back in the 80s I did independent design analysis on the hydraulic hybrid idea. It has a number of advantages starting with a high density energy storage with hydraulic accumulators. With the hybrid advantage of running at constant (maximum engine efficiency) engine speed and feedback from braking and suspension travel, it makes for a nice package. There are some nice cost and reliability advantages over an electric system. I actually got a chance to present to a group at Chrysler; the engineers loved it but the bean counters hated it. As they put it, consumer interest in fuel efficiency was way down the list.

  12. To produce electricity to charge batteries at 80% efficiency, LPG etc. we need to run plants that need fuel of any kind and thus produce polution. Air does’nt

    1. How do you plan to compress your air Franz??? Electricity or fossil fuels to run the compressor = polution…and 80% efficiency on the battery is WAY better than the efficiency you’ll get with air!

  13. Kind of tired of hearing Tata motors next year. Always next year but no results. Somehow I am drawn to constantly look for it year after year. Oh well perhaps the release will come in 2013. LOL I think its a myth.

  14. if a wind turbine at home or anywhere else was used to either compress the air itself or generate electric to drive a compressor this engine would be immediately usable.

    show me the drawback of this engine, considering wind turbines as the power source for compressed air?

    1. Why spoiling good electrical energy to compress and expand air with a terrible bad efficiency, when you can take that energy immediately to an accumulator with an overall efficiency of >80-85 %?
      And that technology exists. You can buy it.
      And there are so many other problems that inhibit the compressed air use in real life. Only one of them is the icing of the engine. While working, the engine gets as cold as minus 40 deg C, so you either have to dehumidify the compressed air completely (costs lots of energy and you cant do that with a compressor at home) or heat the engine while running. Both “solutions” are inefficient and simply stupid, from an engineering view.
      Compressed air has one and only one reason of being: in industry and in explosive sensitive environments. And even in industry, everyone tries to use as less compressed air tools as possible, since it is the most expensive energy carrier that is.

  15. I believe the gents are on the right track regarding energy efficiency, a tankful wouldn’t have enough energy to go very far.

    A better use of air might be pneumatic tube expressways.  Although everyone would sit when there was no wind… ;)

  16. All of this is very interesting and sounds like alot of inteligent people have given good answers; however remember that science says that areo-dynamicaly it imposible for a bumble bee to fly. It is too heavy for the size of its wings.But it does fly, does it not?

  17. That story about the bumblebee no longer applies. High speed photography has shown how the bumblebee uses its wings to generate vortices, and it can be shown mathematically that it does fly.

  18. That’s great Gary and Lew. You guys are getting appropriately philosophical here.

    I’ve got to go with Gary on this one. So what if video with super-high frame rates shows a method of flight that seems to defy physics? The bottom line here is that it happens. I want to be optimistic like Lew, and I’m happy to find the a place where there seems to be some well researched and realistic information along with interesting comments.

    What’s particularly pleasing to me is the increasing interest in alternative fuels. I live in Thailand, where CNG and LPG vehicles are seen more and more. My old car needs replacing, but I’ve been holding out, waiting to see what new technology is on the near horizon. Tata’s release of the MiniCat in August certainly seems unlikely. The lack of any mention on Tata’s website, and the challenges  of a fuel-to-power ratio being feasible with compressed air (as explained here) have me wondering what is realistic. Hopefully, exploration into this approach will continue and someone will find a key to defy what seems unlikely.

    Putting on my tin hat, I’ve also got to mention that the obscenely greedy oil companies might just have reason to intervene. Image their horror at the possibility of such an alternative fuel taking a sizable chuck of their profits. I truly believe that we have been swindled and deceived by the oil  industry for a long time. Here in Thailand, the current petrol price for 91 regular is just over 40 baht ($US ~1.30) a liter, with the price of oil at under $US84. When oil peaked at about $US144, petrol prices were 44 baht a liter. There seems to something seriously wrong with the math here. I really don’t understand the ratio. Isn’t it fairly obvious that we’re getting screwed? World-wide demand for oil has been dropping, but the oil industry isn’t about to lose profits. Constantly increasing profits is like a sick addiction to them. They’ll do anything at any cost to keep the coffers overflowing.

  19. I agree with you about the oil companies in the past keeping new ideas out of the market; however think for a second about what else the oil companies make money on.Lets just start with plastics and asphalt.Almost every thing you can think of is made from plastic. So what if it was cheaper to produce, if gasoline wasn`t used as much. Their profits would go up right? I realize thats a simplistic way to look a it but I think you get my meaning. The oil companies aren`t stupid by any means and the by-products of refining oil are un-believeably profitable. Now old buddy, I`m not defending oil companies but we need to look at our stupid government when it comes to the price of gas. Our government is keeping alot of oil from being produced on government owned land. Having worked in the oil industry I know that when they sell a gallon of gas they make about .11 cents. Take guess at what the average federal and state taxes are on that gallon. Also every piece of machinery used today and well into the future will have to be lubrcated. Anyway new forms of energy have to be on the horizon. I`m esspecially interested in the air-car because when I was boy I asked my father to help me build a device to assist my bicyle with air pressure. My father reminded me of the old fact that for every action their is a re-action. the concept was to peddle my bike pumping air into a small chamber to be released as I needed. That was in 1952, so I`m sure there are alot people much smarter than me thinking about this concept.

  20. It’s a very interesting car but we’ve heard this before over and over again. Please back off unless you have a SELLABLE product. I has to FIRST be on the market then you can brag about it.

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