By on September 28, 2018


hybrid air

Maxim writes:

Just saw your post about running out of questions. Just wanted to say that you have a fan in Montreal, Canada! Love the subjects you guys talk about!

Everyone is talking about electrification and hybridization, but battery cost is a big negative point. PSA (group Peugeot Citroen) has developed a hybrid air system using compressed air as an alternative to electricity. A very smart and cost effective system. Where is that system now?

Why are the manufacturers not using tech like this to reduce their fleet MPG?

Sajeev answers:

The answer is almost always money, honey.

Peugeot isn’t risking it because they’d take a bath. Without the government incentive, why would a manufacturer put their eggs — ANY eggs — in a Hybrid-Air system basket?

The R&D costs, the durability and safety testing of components/subsystems/the whole vehicle, production/marketing of the final product must all be considered. I reckon this “moonshot” is a dangerous investment: only Tesla has the juice (and dat market cap) to make cars while often losing money.

There’s nothing wrong with moonshots: the Toyota Prius is proof. Between a Federal boondoggle Partnership for a New Generation of Vehicles that (not?) surprisingly produced zilch for would-be buyers, the California ZEV initiative, and whatever Jim Press was alluding to, Toyota had ample reason to give their hybrid system a shot in Japan and the USA.

I’m not gonna speculate to the validity of Hybrid Air Systems in the real world of motoring: it’d be awesome to see it hit the road to see the pros and cons firsthand.

But follow the money and you’ll totally see why it had to die.

[Image: Shutterstock user Syda Productions]

Send your queries to [email protected]m. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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33 Comments on “Piston Slap: Depressurizing Compressed Air Engines?...”

  • avatar

    Another Montrealer, between you me and Clavey we could practically have a meetup. Alas I don’t own a Mustang.

    What Sajeev is saying illuminates to me why incentive programs for specific technologies makes little sense. If the same backing were available to any technology based on its ability to achieve tonnes / carbon reductions or fuel efficiency targets, more flexible interesting tech could deploy, no? As I understand it when you have a solar electric program for example, wind energy has to go get its own program, rather than saying, here’s an incentive amount for supplying zero-emissions electricity to the grid. In general we’ve had a bunch of tech-specific approaches. Under a performance approach meanwhile, you’d still have EVs and hybrids doing very well.

    BTW nice shout out Sajeev to the real hero of the revolution here, Toyota for doing the Prius 20 years ago. I hate Prii drivers generally but the car will be proven to be the major achievement of the age imho.

  • avatar

    Seems like another false. Compressed air holds little energy, and compressors have been around for a long time. What’s changed that makes this system work?

    And the counterpoint, what’s changed to make hybrids or EVs work? A lot actually – electric motors and batteries, and a power supply that is steadily dropping in carbon content.

    • 0 avatar

      Exactly, this ^^^ and durability. Compressed air hoses, fittings and tanks are finicky – and even a tiny leak will result in the hybrid system being ineffective. Hydraulic and compressed air hybrid systems have been evaluated by several manufacturers, and they just dont deliver the bang for the buck over the long haul…

    • 0 avatar
      Greg Locock

      Got it in one. The energy density of compressed air in tanks is pathetic, even if you go to very high pressures.

      Then when you expand that air it cools, and freezes up your engine.

      To get around that the smart boys in 1904 added a bit of fuel to the mixture, which gave a huge improvement in range, although now of course you basically have a supercharged diesel engine.

      The company that took this ludicrous concept furthest, recently, was called MDI, and went down the same path of adding fuel to their engines.

  • avatar

    Love me some compressed air cars:

    Water rockets are great too.

  • avatar

    Keep drinking that climate Kool-Aid. There is no reason whatsoever to be concerned about “carbon content” as it is a non-problem; just another excuse for governments to grab more power and steal more wealth. (If you do not believe that is the primary motivation driving governments you might want to check out a history book sometime.)

    I certainly would not purchase an electric or hybrid car based on lithium-ion battery technology no matter how hard government thugs and environmentalist dirtbags want to push us into it. Compressed air? Seems unlikely. Maybe if a super-battery or Mister Fusion type power source is commercially feasible at some point.

    Until then, internal combustion baby – accept no substitutes!

    • 0 avatar

      “There is no reason whatsoever to be concerned about “carbon content” as it is a non-problem”

      see that? Some guy on the internet says it’s not a problem, so it isn’t.

      it’s amazing to me how arrogantly people believe they know way more than they actually do.

    • 0 avatar
      Arthur Dailey

      Well if @2manycars has completed a Doctorate in geology, environmental studies, meteorology or similar applicable subject then he can provide documentation regarding his belief.

      Otherwise over 90% of those with such degrees have expressed their belief in ‘climate change’.

      And the studies conducted over the past 100+ years by insurance providers demonstrate a massive change in weather patterns over the past few decades. Particularly such events as overland floods.

      Personally I rely on anecdote/personal experience, in which I have witnessed extreme weather becoming much more common.

      As for compressed air, having worked in manufacturing, compressed air was traditionally among the least efficient users/producers of energy. Particularly piston compressors.

      • 0 avatar

        I think the question is why. Is it CO2, H2O vapor, particulates, the sun? For example, water vapor is far and away the most influential greenhouse gas with most studies putting it at 95%. The climate on mars is changing as well. Once you get to the root cause of climate change then you can figure out what to do. The earth was hotter than we are now at times in the past. Much colder too. Why?

        • 0 avatar

          Your questions are legit if you are not much knowledgeable in climate. If you want to know what climate scientists actually say regarding climate on Mars and the relative greenhouse power of water vapor vs CO2, the answers are one google away.

        • 0 avatar
          Brett Woods

          There is always that guy who thinks if he doesn’t know, then nobody can know. Curious?

          Here debunker Potholer54 rips through the tabloid debate like a high school boss. But, if you find yourself tuning out during this video series, don’t worry. It probably is like you said in high school, stuff you don’t need to know because you’ll never use it in real life. But please don’t say that nobody knows.

    • 0 avatar
      SCE to AUX

      You don’t have to embrace global warming to like EVs or hybrids. I vote have owned both, and I vote “R”.

      The EV driving experience is the smoothest and most responsive you’ll find, and hybrids simply use less gas – what’s wrong with that?

    • 0 avatar

      Funny how even though its a known fact that the earth’s climate is anything but a static entity (in other words, its ALWAYS changing), we’re constantly told that the only way to combat this faceless boogie man is to line the pockets of politicians and surrender to them our personal freedoms. As to these so-called scientists who ‘all’ agree (forgetting for a moment that any dissenting voices have been ignored), well theyre making quite a lucrative living telling us we’re all gonna die. If there’s no massive problem, theyre all out of a job…does anyone NOT find this at minimum, a bit suspect?

      Doesnt matter to me either way…Im gonna drive my Hemi like I stole it and I dont even know the meaning of guilt for my ‘carbon footprint’. Translation: I just dont care.

      • 0 avatar
        SCE to AUX

        @MoparRocket74: +1, from this EV fan.

      • 0 avatar

        …As to these so-called scientists who ‘all’ agree (forgetting for a moment that any dissenting voices have been ignored), well theyre making quite a lucrative living telling us we’re all gonna die. If there’s no massive problem, theyre all out of a job…does anyone NOT find this at minimum, a bit suspect?..

        Then why would a climatologist accept a modest-paying job from a caring non-profit instead of a high paying one from a fossil fuel company? Those scientists could all make a fortune jumping on the denier side. Its a good thing too. Imagine what all those grossly underpaid researchers making dirt fighting cancer, Aids, etc could make working for a pharmaceutical company…your very life might be saved by them…

      • 0 avatar

        you know what I find amazing? The people who deny this because they don’t want to “line the pockets of and surrender their personal freedoms to politicians” are almost always the same people who are more than happy to sit in a big room every Sunday morning and line the pockets of and surrender their personal freedoms to a man in a robe carrying a book.

    • 0 avatar


      No point in trying to make a solid case with someone who’s opening salvo is “thugs” and “dirtbags”…A closed mind is as useless as a flat tire.

      But regarding the need for a super battery, if one has current experience with what is now available you might find today’s tech works just fine. Last week I had to give back my work-provided Altima hybrid and it was replaced with a 2017 Prius. Initially I was not happy at all – the 2014 Prius that they wanted to give me a couple of years ago was a horrible drive and I gave it back. The 2017 drives much better, not as dynamically pleasing as the Altima, but it will do. On the mileage front, the Altima’s best returns were 42, but 37 was typical. The 2014 returned low fifties. The new Prius? Worst trip was 66. Best trip was 77! I was amazed.

  • avatar

    I think UPS did something similar to this with their trucks a few years back “Hydraulic Hybrid”. Tried to send with links, but caught in the site’s spam filter.

  • avatar

    From 2002-2006 I worked at a company that made golf cars and off-highway utility vehicles whose corporate overlord was a big name in air compressors and air tools. The corporate types loved leveraging expertise across business units and always came up with goofy collaborations to make money.

    Someone announced an Air Hybrid tech/demo during my time there. Naturally some executive type thought if we could pull it off it would be his ticket to the BoD.

    The concept spectacularly failed an initial engineering analysis. The pressure the on-board storage would have to have been charged to would have been lethal in any minor mishap. Decompressing a working fluid that much would have caused thermal and icing issues anywhere other than Phoenix in August. On top of that the cost to recharge would have been orders of magnitude higher than gas or electric and the purchase cost would have been higher.

    This is really why the idea hasn’t gone anywhere.

  • avatar

    Battery cost *was* a big negative point. Currently I doubt there is any cheaper and lighter way to store electrical or mechanical energy (aka exergy).

  • avatar

    Having witnessed a catastrophic pressurized tank failure, (too keep it light, a coworker now goes by the nickname Stumpy). I would not want to be in a vehicle with a compressed air system. A 125 psi tank on a tractor trailer is a lot different from the 4500 psi or higher that is needed to move a vehicle.

    To make a tank strong enough to withstand the needed pneumatic pressures AND survive an accident means a very heavy tank, which hurts the compressed air vehicles range and practicality… a similar issue electric cars have with batteries.

    But I’d much rather risk the fire hazard of gas, diesel, or even a lithium battery. With those you at least have a chance of exiting the vehicle to save your life.

  • avatar

    golden2husky: Oh, yeah – them thar smarty-paints sah-in-tists is a-gittin’ rich, pickin’ on them POOR fossil-fuel comp’nies, whut ain’t got NO muney! A ex-purt with orange har, done tole me!

  • avatar

    As Scotty might say, “Ye cannae change the laws of thermodynamics, Jim!” The energy efficiency involved in compressing and expanding air is very low.
    In the bottom of a mine where you might run in to pockets of methane, you can operate vehicles by running an air hose down from a honking big compressor, and plugging it in to a modified ICE engine. It’s not efficient, but it avoids explosions. Your bulldozer or pickup truck is tethered to a hose, but it’s in a mine, not driving on streets.
    Compressed air engines, like fuel cells, are only applicable to very limited applications where overall thermodynamic efficiency and cost is superseded by some other requirement, like operating in explosive atmospheres or outer space.

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