A Blow For The Compressed Air Car

So earlier this week, I posted a video about a pair of compressed air cars under the heading of “A Little Competition for Tesla Motors“. The post got picked up by one of the Tesla discussion boards, and as a result, it attracted some informed comments. The last comment on that post, however, is worth cross-posting here.

But how much energy is required to compress that air? How efficient is the compressor? Perhaps at most 60%? Then what is the efficiency of the engine running on compressed air? So instead of using energy to compress the air with a 40% loss, then run it in an compressed air engine with further losses, isn’t it more efficient to run an electric motor? If you’re [using] solar panels, wind, hydro, nuclear to produce [electricity], then you can’t beat an electric motor at efficiency. The less energy conversions the better.


23 Replies to “A Blow For The Compressed Air Car”

  1. “The less conversions the better” – well indeed, but did I miss some irony here? In case I didn’t…

    You don’t need a generator on a wind turbine to drive an electric compressor, you can more simply drive a compressor shaft direct from the torque of the turbine, skipping all the conversion steps.

    Similarly you needn’t use solar panels to produce electricity and then use that electricity to drive an air compressor. Gas expands when heated & contracts when cooled very efficiently – solar energy capture yielding compressed air (using a stepping cascade of interlocked pressure-vessels) would use less conversion steps than a car motor driven by solar-photovoltaic (panel – collection grid – chemical battery storage system (charge) – reconvert (discharge) – transmission system / inverter – electric motor)

    I like the air motor. So much so that I thought it was a joke when I first heard of it 6 or 7 years ago.

    1. Another way of making this work would be a plug in hybrid compressed air+electric vehicle. When the vehicle is charging, an electric motor powers a multistage piston compressor that is intercooled between stages by standard auto coolant technology. The heat of compression would be stored in an insulated tank filled with paraffin or a eutectic salt solution. The compressor and air tank(s) would also be insulated to minimize heat loss.
      When the vehicle is running the compressor becomes a multistage expansion engine using the stored heat to heat the expanding air. This air heating can be enhanced by using the waste heat from a small gasoline engine. A small scooter engine perhaps. This would boost the power and range of the compressed air engine. A piston engine would not need a transmission (similar to a steam car). There could still be a need for electric motors and batteries but it would be reduced. Batteries are expensive. The gasoline engine could power the electrical system of the vehicle and/or power an air compressor to help power the vehicle.

  2. I believe everybody is missing the point here, efficiency is a very small part of the problem or the solution.
    Firt it is very ineficient using gas to move a car but for the last 100 years it seems to have worked just fine.
    Second you can use a lot of different ways to compress air, and there is a lot of things that you can do with that compress air.
    The good part is that the tank that you use compress air doen’t need much of maintenance and you can recharge almost for forever.
    I believe that the use of compress air to move a car is a great idea. You can have a compressor in your house compressing air all day and at night you can transfer that compress air to the car tanks.
    The greatest problem for the compress air car is that uses not much oil, I believe uses a liter of vegetable oil every three month, and It doesn’t need much of maintenance, so what are you going to do with all the oil changing places in the country and with all the gas stations in the country, and with all the people that works for them?
    that is the main problem!
    The same problem is for the electric car it was too good, Hybrids are getting in the market because basically they do not alter the way things work.

  3. Gentlemen: Thanks to both of you for the thoughtful posts.

    @ Mike: Certainly the wind turbine directly driving the air compressor removes a number of steps, but I don’t really see us bringing wind turbines into the cities (or for that matter trucking compressed air in from the wind fields to the cities). On the solar panel (heat not photov) idea, is “a stepping cascade of interlocked pressure-vessels” feasible in a home garage or a neighborhood air station? Note, I am not trying to be flip here. I (obviously) have no idea how these technologies work. But I am interested in learning more about how someone does this at home (or buys air from some guy/gal down the block).

    @ Oscar: Social point noted. And it certainly is a strong point when you focus on the lobbying efforts of the major oil companies. However, a similar argument was made just before the end of the conflict in Northern Ireland. Specifically, people were concerned about how you live with peace when generations of folks only know war? The IRA fighters (generally) did not have a trade or a profession (and for darn sure, the UK military was not going to accept them into the only line of work relevant to their training and experience). Luckily for all of us, peace did hold. I have every belief that if we can overcome the hurdle of the major oil companies (and that is a big “if”), that the corner fueling stations and corner oil change stations will morph to serve some new need in the personal transportation sector….and I do hope that my belief is correct.

    1. That was a confidence builder, the statement at the top of this box saying, "Replying to Jerry." I was hoping to reply to you but got a little lost in the exchanges. I realize this is a pretty late reply to something you started in 2007, but hopefully something pops up to tell you there's a late comer out there. Where do you get the phrase, "a stepping cascade of interlocked pressure-vessels?" What do you think it means?

      I'm often amazed how many dissenters there are out there ready to pounce with such authority and vehemence on every sort of hopeful look at a possibility, but has your inquiry into compressed air driven cars dried up? Now, two years later, do you know any more? Just wondering.

      Michael Moreland

      1. Michael:
        Sorry for not replying earlier. Your comment got lost in the noise and I just now found it. The phrase to which you refer is in the March 16th comment from Mike Langridge. I don’t know what that phrase means, but he apparently does. I’ve sent an email asking him to re-engage with this thread. We’ll see what comes of that. Thanks for the comment.
        — Jerry

  4. Oscar’s idea of oil companies quashing any motive power technology that requires no oil has that urban-myth-logic appeal. Ther’s a story that match companies bought the patents to an everlasting match – then made sure the idea never got to market, hmm.

    It is a more powerful argument to point out that renewable distributed energy systems don’t offer the concentrated capital requirements / opportunitites that contemporary centralised generation does – so distributed systems can’t catch on in a big way in a capital driven culture – the way organic locally grown vegetables can’t.


    The second point was mine, I didn’t say “compressed air is a credible way of powering all vehicles” I said the number of conversion steps was overstated by the assumption that you step through electricity.

    Airpower is far from useless. Sail boats used it for centuries, trapping a tiny proportion of the total energy available across the ocean – in comparatively tiny sails. Adding wind turbines to cities is trapped-thinking, like putting a car engine before a horse-cart and saying it looks ludicrous – it does.

    If wind were trapped and used in cities then buildings themselves would incorporate the morphology – at it’s simplest and most clunky roof and corner surfaces might include linear turbines – barber-shop spinning signs, arranged in linear grids like external venetian blinds – I already put static grilles on buildings to hide roof plant. The wind is weak but even houses are huge compared to cars, and would collect wind passively 24/7 – most cars are driven under power for around 2 hours per day or less. There was a time when buildings were built to house such surfaces, rather than the surfaces being added to the buildings – they were called wind-mills and they worked very well.

    I’m not hung up on air power and I dont believe it’s the answer by the way – but it would have taken a huge bomb to blow out New Orleans – wind power is real – and a gentle usable energy discharge breezes past us every day.

  5. @Michael: Again, thanks for the comment. Your last paragraph begs one question….and I just have to ask it….is there anything that you believe could be the answer? … for personal transportation and/or energy in general.

  6. Jerry, thanks for your reply, which again forms two questions.


    I believe there is a better answer (a means to enhance human physical mobility, being superior to the motorcar in every way, and sustainable). I’ve been tuning this for 15 years now – harmonising it with the different current social, temporal, economic and psychological environments we live in to pitch it to take off, survive and thrive as a worldwide paradigm.

    If I have not wasted my time then I may have overcome some daunting funding, administrative, marketing and political issues. There are no technical obstacles, it’s been my life’s work.

    Energy “Answer”

    Ultimately this may be as false a horizon as the concept of the edge of the earth, prior to our consciousness of gravity and spherical bodies. It may be that we will freely and electively consume a hundredth of the energy we do now as a matter of taste. Ridiculous and dismissable perhaps, but we rarely shout at the height of of our voices, and don’t restrain ourselves in this from politeness to our surroundings: it just isn’t ‘classy’ behaviour to shout. Furthermore we choose not to sate our appetites endlessly, competitively eschewing obesity. Our addiction to consumption of all types is a search for love and satisfaction. There is no single answer to anything.

  7. @ Michael: I am not looking for a single answer — nor am I that naive.

    But I am always looking for “new possible answers.”

    And I am not trying to put you into a box. Given your comments so far, I am merely interested in answers that appeal to you now. For example, your reference to vertical axis turbines introduced me to a technology that was previously unknown to me. This compressed air car technology was interesting to me, again because it was previously unknown to me.

    My question to myself (and to you) is what else might I be interested in (e.g., plug-in hybrids)? You make reference to a 15 year quest but do not elaborate. I can only assume such omission was intentional. Is there anything that you can share or want to share?

    Is there anything that you would like to see me (an outsider to the clean energy industry) talk about? I am in a talking mood (with you and others).

  8. Thanks Jerry, I can tell you’re not naïve. When I said there was “no single answer to anything” I was being wistful, I wish there was.

    I just typed up a suitable precis of my 15 years thoughts, it took 2 hours to condense it to 3 paragraphs and still make clear sense. Then I lost it when my wife plugged in our faulty iron downstairs and the house tripped out.

    For transport my answer boils to down to the elective uptake of NEVs by consumers on a massive global scale to usurp the car. I’ve spent 15 years thinking this through, ways to make it happen / allow it to happen; make them so that people prefer them to their own cars; create structure so that capital enters, making more return in NEVs than it does in oil and motorcar production; adopt built-in recycling that I call “recursive manufacturing” so that re-moulding the materials / modules becomes as natural to the business as …….circulating blood cells in a body (would you ever make new blood cells all the time to use once?); I was onto V2G eight years before I ever read it on here. There are no technical barriers to any of this; all the barriers are all about overcoming dominant paradigms and administration with a critical mass of change – proving it’s profitable and setting off a chain-reaction freely funded by capital.

    For “energyâ€? and natural resources my answer boils down to the recognition that it’s capital and it’s growth pattern that’s consuming too much energy, not humans. Capital is the dominant living entity on the planet, not humans. Capital systems grow and colonise to exclude less successful entities like wildlife. Humans serve capital, not the other way about. More powerful than us, capital lives with and around us and I’m not suggesting we kill it (who’d want to? It’s as good eating for us as buffalo) but we need to attune capital to its external environment – it’s already killed the real buffalo (humans didn’t) and will trample over us soon the way it’s going. Capital guides our behaviour, but itself would need therapy. Yet it can fund but not think, it just needs to grow and live.

  9. Michael:

    There is a lot in your comment to digest and I will post more when that happens.

    One point I would like to offer now…I believe that Gore’s film has pushed society closer to an inflection point on environmental issues. I really think that we are on the verge of a popular movement away from oil. And I believe that when China fully comes on-line, its demand for oil will dry up supply and keep prices high enough to justify alternative innovation. Car companies like Toyota (riding a “hybrid” wave) are making Detroit look like a Dinosaur — and I really think this is only the tip of the product line iceberg (with upstarts like Tesla also showing early promise). And I hope that I am right.

    I also notice that a number of my friends are moving beyond organic (towards community supported agriculture, etc.) in response to books like “Natural Capitalism” and “the Omnivore’s Dilemma”. The key for these people (as I listen to them talk) is to find food that is not merely “healthy” but “anti-institutional” and local. If this is more than just a fluke (and no I do not live in Berkley, CA), then the paradigms that form the basis of your lament may be toppling soon. I hope that you (and folks like you) will be ready with your push to offer alternatives when those old paradigms collapse.

    Oh and before you disappear, I do want to say “All the best to you and thank you for this discourse.”

    — Jerry

  10. Your friends sound amazing.

    ‘Shame they’re not typical of the US population – my ideas seek to change the habits of the most cynical, lazy and least motivated “I” – the collective sloth in all of us in the UK, US East and West alike.

    If you’ve not seen the Robert Newman Oil sketch / lecture on oil you really should, it’s on Google Video (you search Robert Newman Oil – but you knew that, I said it for “the gallery”)or you might be able to link direct…


    we’ve gone from whether it was “a blow for compressed air” – but I stand by my original post – the number of conversion steps was overstated, so the comment wasn’t “worth cross-posting here” except as a provocateur. I like your site Jerry.

  11. Michael: Provocations are not really my style, but I must say that the dialogue was fun. Oh, and yes, my friends are amazing. BTW, you have already met Scott and Ben in the other thread.

  12. couldn’t the car have a built in air compressor that runs from the air engine, this compressor would keep the tanks topped off. all that would be needed would be a full tank to start off with, then the cars own compressor would keep it going…
    just a thought.

  13. Thanks for the post. Actually your post is a bit interesting because it misses the very same principal that I missed when I first posted this thread — namely the principal of entropy/irreversability. In particular, the concept your comment hopes for is a perpetual motion machine (a machine that can generate more energy than it consumes — thereby permitting you to run the car and “top off the tanks” at the same time). If you can figure that one out, please email me. I would love to see it. 😉

  14. Hi Mike, Jerry,
    I am interested in both your sides of the discussion. I would like to hear more about applying the technology. Please send me some info on it.


Leave a Reply

Your email address will not be published. Required fields are marked *