What’s the status of Compressed Air-Powered Vehicles?

In the blunder years of Youtube I remember seeing endless videos about ‘air-powered’ cars & engines. A lot of them involved perpetual motion, which my young brain attached onto obsessively. The government was hiding these devices. It was all a big cover-up. “Mom! We’re out of tin foil!”

“MOM!”

Sooner or later, after watching some of these videos more carefully, I realized that the reality of the situation was much more mundane. The fact of the matter was that you could make an engine run on compressed air. Ah. Of course.

As it turns out, compressed air vehicles don’t make a ton of sense. The energy density of compressed air is piss-poor (worse-than lead-acid batteries). If you attempt to increase this density by vastly increasing the pressure, you get a slightly less piss-poor vehicle that’s also a bomb. Ever seen a tire explode?

Batteries today are safer, and more energy dense. You don’t need a compressor to pump the air into the car and you don’t need a complicated engine. You’re skipping the middle man by going fully electric.

That doesn’t mean people haven’t tried.

Starting with Air-Powered Bicycles

Air-powered bikes are a popular project for university students and tinkerers. They’re not quite as time-consuming (and frankly, life consuming) as making their steam-powered alternatives.

There currently aren’t any you can buy commercially, because the range on a relatively low-pressure air powered bicycle is pretty bad. A smart Youtuber named Tom Stanton made one, and his was capable of about 3/8 of a mile.

Now, you may be thinking, what if he (instead of the BORING 120 psi) cranked that contraption up to something like 3000 PSI? Evidently several French people had the same thought you did.

The AIRpod

No, not the headphones.

The AIRpod is, well, a concept. The French company who makes them (Motor Development Industries) has been promising a production version for more than two decades. To quote Samir from Office Space, it must be nice to have that kind of job security.

Tata (the Indian automotive company) has a partnership with MDI to make an air powered car, as does a company in the United States. Although things appear to be happening at a snail’s pace, MDI has released a technical document detailing how the whole thing works.

The engine that receives the compressed air is a 430cc two-cylinder. MDI says it’s reversible, meaning it likely works the same way many steam engines do (every stroke is a power stroke). It claims to have variable valve timing, and the whole thing is made from aluminum.  Maximum power is 9.4 horsepower, which, even by 430cc standards, is pretty weak.

It has an automatic transmission, which I’m supposing is of the CVT variety, since no quantity of speeds is listed. This all seems pretty tame so far. The more interesting part is the compressed air storage.

That’s a lot of pressure!

The air is crammed into in two plastic-lined, carbon fiber tanks. They’re 125 liters each, stored under the passenger compartment, and are pressurized to 3600 psi. That’s about 245 atmospheres a piece. The extreme pressure leads to a reasonable range–supposedly around eighty miles–but thats also because of the vehicle’s paltry weight; (allegedly) 617 pounds.

The car is small–the wheelbase is only 58 inches. Its minuscule size and weight are also not the only contributing factors to its range. The AIRpod’s max speed is just fifty miles-per-hour.

This information is explained in much better detail in MDI’s presentation-like document on their website, but all of this engineering doesn’t change the fact that these sort of vehicles are just doomed to fail by their poor energy density.

So why are people trying?

Advantages

Air-powered vehicles are pretty much the most environmentally friendly type of transportation there is. When it comes down to it, an air powered car has absolutely zero emissions. In addition to this, the materials used to make them can be almost entirely eco-friendly and recyclable. There’s also no messy batteries or tailpipe scum. The factory making them is really the only possible source of pollution.

Another interesting advantage of compressed air cars is the air-conditioning system. Ever bought a cheap, gas-operated airsoft pistol on Amazon, shot your brother with it repeatedly, and then removed the empty canister to feel how chilly it was? You could put a big heat-exchanger onto the air tanks and have free A/C. There’s no hazardous refrigerant or complicated compressors required.

Air tanks also don’t lose any energy density overtime like batteries do. An air-powered car parked overnight without charging wouldn’t lose any range. The same cannot be said for most EVs.

Finally, they’re cheap to make. There’s no spark plugs, catalytic converters, cooling system, batteries, etc. It’s just some air tanks, hoses, and hunks of aluminum with big holes drilled in them.

None of that really matters, though.

If you were driving a fully-inflated air-powered car, and got hit by another vehicle, it would kill you. Although I’ve heard being vaporized in an air-powered car is actually very peaceful, I’m not so sure myself.

The lack of efficiency inherent to compressed-air powered vehicles is also more-than often tackled by adding… uhm… a gas engine, or batteries. The hybrid versions of these drivetrains theoretically have the most promise–primarily in buses–but concepts have yet to hit the streets.

They also need compressors to charge them, which are loud. Considering most people charge their cars while sleeping, this may cause problems.

There’s a lot of other disadvantages, too. If you would like to read all of them, the Wikipedia article concerning air-powered cars is very well done.

Stick to the dirty stuff, then.

So, as it turns out, a clean air-powered future doesn’t look so good. That’s too bad, because the rare-earth metals found in EVs are much dirtier than most people realize. A popular method for mining them is to dig a big hole, get all of the valuable metal out, and then pour all of the mining slag back into the hole you dug. If you’re not so keen on doing this, you can just have kids in Africa do it.

The alternatives to gasoline are gradually getting cleaner, but there is yet to be a breakthrough. Hydrogen looks pretty good, but it’s still very expensive. Its a shame compressed air doesn’t work very well, but I suppose we’ll just have to keep waiting.

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17 responses to “What’s the status of Compressed Air-Powered Vehicles?”

  1. danleym Avatar
    danleym

    I regularly wear a bottle on my back pressurized to 5500psi. A brief google search says CNG cars (and there are plenty of them) run around 3600 psi. The pressure doesn’t concern me.

    Also, you have to compress the air somehow. That compressor will have emissions of some sort, unless its fully electric and powered off of solar panels/wind. Just the same as electric cars aren’t truly zero emission- they’re only as clean as their source of electricity.

    That said, I had no idea this was a thing, so thanks for sharing!

  2. mdharrell Avatar

    Vaporware.

    Perhaps it’s just as well, although I keep thinking that, inasmuch as MDI had at one point reached an arrangement for setting up manufacturing in Hawaii (!), there may be at least one or two of their prototypes still sitting around inside the US. I’m pretty sure they could be titled and registered as mopeds here in Washington, despite having no pedals and four wheels, in that the front two are close enough together to count as a single wheel for legal purposes. Not that I’ve given the matter much thought over the years…

  3. smalleyxb122 Avatar
    smalleyxb122

    In the early days of the automobile, there was a car that used a giant spring for power. The Burdick. There is a curious lack of information online about it.

  4. 0A5599 Avatar
    0A5599

  5. Professor LavaHot Avatar
    Professor LavaHot

    I’ve always wondered if you could use this technology for regenerative braking, charging up a bottle as you go from 30 to 0 at a stop sign, and then opening it up into an auxiliary engine to get you from 0 to 10, 0 to 15 or so… just to see what kinds of fuel savings would happen (probably not a lot). There was a time when I heard UPS and/or Fedex were looking at a similar hydraulic concept for their trucks, but it must have been a dead end.

    1. Monkey10is Avatar
      Monkey10is

      ‘Hydraulic hybrid’ sounds like a tempting idea (combining two technologies we understand) but unless you have another reason for wanting hydraulics — perhaps a backhoe loader? — an electric hybrid is generally a better plan. Compare the mess of high pressure hoses, hydraulic fluid (with its compressibility, and tendency to alternately absorb water or precipitate out gases) etc. and the complicated valve assemblies needed for any storage vessel with a simple generator-battery-motor set up.

    2. Monkey10is Avatar
      Monkey10is

      ‘Hydraulic hybrid’ sounds like a tempting idea (combining two technologies we understand) but unless you have another reason for wanting hydraulics — perhaps a backhoe loader? — an electric hybrid is generally a better plan. Compare the mess of high pressure hoses, hydraulic fluid (with its compressibility, and tendency to alternately absorb water or precipitate out gases) etc. and the complicated valve assemblies needed for any storage vessel with a simple generator-battery-motor set up.

      1. Monkey10is Avatar
        Monkey10is

        (For a simple stop-start operation suitable for FedEx etc. then perhaps generator-capacitor-motor is better suited. But the (understandable) push towards plug-in hybrids and BEV suggests that the research and money goes towards developing battery tech more than into capacitors— so we may have already chosen a path away from capacitors.)

        1. outback_ute Avatar
          outback_ute

          I think capacitors are still ‘there’-ish, they can be used in household/commercial ‘battery’ banks instead of batteries, and Toyota used them in its Le Mans car a few years back.

          Peter, not sure about claiming 9hp from 434 cc being weak – comparison to ICE engine efficiency isn’t really valid.

          I’ve heard of compressed air service vehicles (variation of a JD Gator?) being used on golf courses where range & recharging wouldn’t be an issue, otherwise for road use I can’t see it working – too much energy loss both in compressing the air and in powering the vehicle.

    3. neight428 Avatar
      neight428

      Kind of sounds like KERS with an additional form of energy storage and mechanical complexity in the mix.

  6. SlowJoeCrow Avatar
    SlowJoeCrow

    I saw a small car converted to compressed air by a college in Missouri in 1993 with posters hyping it as the future of propulsion, it seemed pointless then and it’s still pointless now. The power density of compressed air is poor, so low power and short range plus the whole problem of having air compressors and powering them. At least electric charging stations are quiet. The only useful application I can see is explosive environments where even intrinsically electric systems are too risky.

  7. crank_case Avatar
    crank_case

    At the risk of sounding like a tin foil hat wearing nutter… these have actually been indirectly suppressed by government policy, but maybe not your government. PSA were doing serious research into compressed air hybrids (which I guess isn’t surprising, because Citroen), but decided not to pursue it further, because even though it promised the same benefits would not qualify for EU subsidies in the same way that battery tech would.

    https://www.groupe-psa.com/en/newsroom/automotive-innovation/hybrid-air/

  8. neight428 Avatar
    neight428

    Doesn’t this all then go back to the efficiency, emissions, etc. of whatever is used to power the compressors that will fill a bottle up to a jillion PSI? That potential energy has to be converted from something else.

  9.  Avatar
    Anonymous

    I think it’s a viable option the only reason not to pursue it is it would put a lot of people without jobs! I know of one that was built locally and drove the Florida and back! He got bought out by the big three

  10. Ron Avatar
    Ron

    Hydraulic regeneration has heat and turbulence losses of 20%, the losses with electric regeneration are 60% or more, air is similar to hydraulic. Guy Negre was a F1 engineer and the understood the physics, Tata motors bought it, millions of investment from savvy sources, this is viable especially since renewables can play a large part and thermodynamic solar compressors with rankine cycle for electric charging as well are doable with simple heat storage, the status quo has never been maintained for lack of solutions. The motor Guy came up with was genius, articulated conrod, two different sized cylinders, heat exchangers and capable of running on petrol too. Citroen are doing a version now, Given 80% of all travel is under 80 miles there is definitely a place for the compressed air car especially with lots of stop and start like taxis, 10 hours of driving is a shift, you can blow it up really fast from a storage tank and the freshly decompressed air from the exhaust is cool and cleaner than the air coming in the window because you can filter it on the way in and run on a net less-than-zero emissions actually and no extra energy for aircon. Small is efficient, carbon fibre kevlar tanks are pretty safe compared to high voltage dc lithium packs and petrol tanks. This article is shy a few facts and makes for a pretty poor argument.

  11. john ibbertson Avatar
    john ibbertson

    im a retired electrician who believes compessed air driven cars could be achieved , the energy from 300 psi is pretty phenominal as in air rifles. so lets get on with it as fuel prices are ridiculous.

  12.  Avatar
    Anonymous

    The main problem is that Mankind has not placed enough significance on Pollution… as it has on Cost.. Money etc…

    Once you include this ($0.28/KWhe) and possibly $50/kg (???) on ” Safe Disposal Cost” off Dead Batteries .. the “economics” will change totally…. as Heat Recovery Systems for Air Compression further
    upset the ” Energy / Efficiency Balance” of using Compressed Air…

    This is no different from why we con
    tinue to use PollutingvFossil, Nuclear Fuels today … that enjoy no penalty for the above Societal Cost of Pollution …. and therefore c
    ontinue to Pollute, spread Death & Suffering… all over the Globe..