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Monday, July 7, 2008

The Pneumatic Car

Note to readers:

I am receiving post after post in fevered rebuttal to this little post on pneumatic cars. The problem is that most of the rebuttals seem to be reacting to something other than what I have written. So I am going to try to set the stage for my essay in such a way that these misunderstandings disappear.

First, I am a student of thermodynamics and know full well the inefficiencies involved in the process of compressing a gas. It is obvious that less energy is lost to the charging of modern electronic batteries than is lost in in the process of storing energy in a high pressure air tank. Compression works against efficiency in lots of very real ways. Not only that, but the release of this energy through decompression is also inefficient. The relationship between heat and pressure is a bitch and always works against such schemes.

But that is not the point of my post. I am attempting a larger system-wide solution that takes into consideration efficiency metrics not limited to the power-plant of a vehicle. I believe that there are aspects to the compressed air vehicle solution that more than out-weigh the obvious inefficiencies when measured purely from an energy storage density perspective.

To wit: Purely compressed air cars are much much much more simple than electric or hybrid cars. That means they can be much much much lighter. Ultimately, it is the weight of a vehicle that most determines its energy demand.

But most importantly, I keep being slammed by people claiming correctly that it would be ridiculous to use electricity to compress air. Absolutely ridiculous! Which is why my proposal so clearly does not require the use of electricity to compress air. My proposal is to only compress air using gas burning turbine compressors installed at gas stations. This strategy is supported by many logical arguments. For one, it takes advantage of the incredible efficiency of transferring energy as refined gas. It takes advantage of an existing extraction, refinement, and delivery system that brings energy to every community in the developed world. Pollution is vastly reduced (order of magnitude reductions) through the use of scrubbers installed on a relatively few turbines as opposed to today's solution requiring each and every vehicle to cary its own exhaust scrubbers.

The combination of super light weight vehicles and the use of an already well established energy delivery infrastructure means it will vastly cut our emissions, cut our energy/mile demand by 70 or 80 percent, more than halve the cost and materials to build vehicles, avoid the natural resistance of change by established industry players (big oil, auto manufactures, gas stations owners, roads and highways, etc.).

And, my plan will not increase demand on our already limited power grid in the way that electric cars will.

It seems obvious to me that it is easier to build high pressure tanks (we know and we have the materials), than it is to build batteries. The best batteries we have today use rare earth materials, our access to which does not scale with projected demands. Batteries are heavy. Batteries have limited life-spans. The best accept fewer than 500 charges. That is less than two years of nightly recharges! Batteries are super expensive. Each Tessla sports car has six thousand eight hundred laptop sized batteries that must be configured within a complex and expensive refrigerated enclosure with sophisticated charging and optimization control computers. Who pays for your knew batteries after two years? Where are they disposed? What is the ecological cost of mining lithium from mile high strip mines in Bolivia, of disposal and recycling, of carrying the weight of batteries around?

Recharge of compressed air tanks at gas stations should take less than a minute. Even if a tank can provide only 50 miles between compressions, the distribution of gas stations means drivers are never far from a quick refill. Tanks can be refilled thousands of times without ever loosing capacity.

Until we have fusion reactors, our only reasonable choice is to use oil for transportation energy. Our choices then center around how efficiently we use oil and how little of its byproducts reach our environment.

Despite its limits, compressed air has the potential to be the best realistic solution to the complex and interdependent set of energy problems facing transportation today and well into the foreseeable future.

[the author]

One of the most brilliant "green" ideas I have seen is for compressed-air powered (pneumatic) cars.

The car is super simple. Each wheel has a little compressed air motor (like the ones in the pneumatic wrenches at auto shops) built right into it. So there is no transmission and no central engine and no drive train to get that energy out to the wheels. Just a high pressure tank or series of smaller tanks (hundred thousand lbs per square inch), and high pressure lines out to each wheel. The vehicle is much simpler and much lighter. There is no toxic or combustive chemical fuel on board. A tank of compressed air is heavy but not nearly as heavy as batteries. You can replenish the tank in seconds. Standard fuel is distributed to gas stations same as today... but it never leaves the station. This is important because gas is efficient to distribute, and because solutions that usurp the oil economy status quo simply don't happen.

At the station, you can start with a traditional piston-type compressor and later transition to a high efficiency turbine engine (like a small commercial jet engine) which burn gas or diesel to compress air in large holding tanks. Big central scrubbers and catalytic converters clean the exhaust from the compressor's turbines much more effectively than can be done today in the tail pipe of each and every car. The cars will go about 200 miles per refill. The cars are far cheaper to build... the third-world can afford to go modern! The biosphere can afford the third-world going modern.

A car without a gas or electrical drive system can be built with a lighter structure, which means they can be built at about one fourth the weight. So, the cars will be at least four times as efficient. Compare this with electric cars which are actually a third heavier than their gas counterparts.

This is a plan that could happen. It doesn't disrupt the current hydrocarbon infrastructure. It does away with much of the problems associated with an oil economy. For one, most of the carbon and green house gasses are filtered and sequestered. The cars use much less fuel per passenger mile driven (up to 200 mpg should be achievable). There are several companies already designing and building the necessary components... some tooling up to build the cars.

Because they won't have quite the range of gas powered cars, you will have to go to the compression (gas) station more often. But, once you are there, it takes less time than filling a gas tank. Compare either with how long it takes to recharge a battery. Then there is weight.

Todays cars weigh in at 3000 to 6500 pounds. Most of that weight is structural support for the engine. A four passenger pneumatic car might reasonably weigh less than 800 lbs.

Another huge and frequently ignored contributor to greenhouse gasses and energy use is the production of new cars. The pneumatic car has about 25% the number of parts as in an internal combustion powered car (even fewer than in the super-complex electric/gas hybrids). That will result in huge (50 to 70%) pre-purchase carbon footprint reductions, and far less materials being consumed. Eventually, as we figure out how to get more energy from the sun, we can move away from hydrocarbons powering the compressors. But even in a hydrogen or pure solar economy, it will still be more efficient to run pneumatic cars than to put a mini power plant in each car (as we do today).


George said...

I agree, and there is a company that is planning to import a new version of the AIR CAR to the USA! We know TATA motors has the rights to build the car in India (I'm not sure about other countries) but this other company just told Popular Mechanics that they got the rights to actually build assembly plants here in the USA! You can find out more at

Randall Lee Reetz said...

Yes I know of the Air Car... I hope it meets with some success. I am also aware that their solution is a central motor sending motion out to two wheels via a drive train of some sorts (direct linkage or chain?). This feels a lot less elegant to me than the motor-in-wheel solution I propose... but there are certain (simplifying) advantages to a single motor solution. They have spent a good deal of their R&D effort towards the design of an efficient pneumatic motor. There are a great many thermodynamic parameters to get right with this whole solution.

The big issue though, the issue that makes me excited about pneumatic vehicles is the larger issue of how the energy is delivered to the car. If the solution simply involves plugging a compressor into your home electrical network... well you are really taking a giant step backwards. Of course the positive side of even this early solution is that the Air Car people are having (for practical reasons), build a really light and simple car. Light cars use less energy. The fact that you have to plug it into the grid puts it into the boutique category (if more than a few people buy and drive these things we are going to be in for some real trouble getting enough energy out and onto our electrical grid).


didier said...

Hi, may I recommend my site to you? It has much information, lots of pictures, videos aned links and the latest news about pneumatic cars.
I do not agree with you Randall, about the electric grid being in trouble if many people use the socket at home to compress the air for their air cars. On the contrary, as an increasing percentage of our energy will come from wind, the grid will encounter serious balance problems. It will be overloaded when there is too much wind and little consumption. For the cars all combined to work as a giant energy buffer, a mobile reservoir, we need one third of our cars to be on the grid. With a smart and well interconnected grid, that gives a signal to consumers at home automatically piling up compressed air when the wind is blowing hard, the grid unbalance problems could be overcome. I have read several articles about this option, be it regarding electrical vehicles, as in

I found your article very interesting, Randall, thank you!


Chris said...

iPower - Intelligent Power - using Smart Grid is what is needed.
IT MDI-Energy are developing this technology using MDI Compressed Air Engine integrated into power grid through IndraNet Minder. Smart Grid is the key to combining, wind power and other alternate forms power generation. They expect to have a solar content within 3 yrs. Imagine being able to generate your own power to fuel your air car.
Check out and

Randall Lee Reetz said...

I think all of you might want to revisit your first year physics lectures. The amount of energy spent pushing a 3000 lb. auto around at 65 mph even for just an hour far exceeds total domestic energy use for a day. Which means charging an vehicle from the electrical grid will demand over twice the energy currently feeding the home. Simple physics, simple math. Wind and solar currently produce for about 3% of CURRENT use. Double use and your green contribution drops to less than 2%. Most home solar/wind systems can barely supply non-transportation demand of that home. I must be missing some magic here? How are you planning on achieving a 2 fold increase (2000%) in the output of domestic solar/wind energy? I am all for it, but I just don't see it. No "smart grid" can PRODUCE energy. As important as smart grid improvements are, they are improvements in efficiency... wasting less of what is there... not production.

Lets get real so that our critics can't question our credibility.


Karrde said...

I'm not trying to be rude to you Randall but I always love reading peoples comments on sites like this where they say "come on people you need to revisit your first year psychics (or math) lectures, and you will learn the truth about how this technology wont really work". It is a fact that mankind has decided not to always use 'simple physics or math' and to use the full extent of our brain that has made it possible for mankind to advance beyond Neanderthal and move into modern day man.

If man had not dreamed and thought about what might be possible then we would still be using stone tools and living in caves. The wheel and every other invention would not have been developed and we would still think the world was flat!

It is the mere fact that man has thought outside the square that every invention and device you can see around the world today has come about because of someone thinking just a bit differently to someone else (were not all mindless drones)

So before you tell us what cannot be done or achieved just because you have done 1st year physics (like every other person on this earth) just try and think outside the square for a while and dream what might be possible instead of telling us what isn’t possible.

I had a read of what Chris wrote and looked at some of those links and if this sort of technology is real then the world is heading in a very different direction in the future. I think you have missed the point slightly. The drain on the power grid will become less as smaller decentralized power units come online to replace the huge inefficient legacy power plants that we currently have. Smart power grids are sure the way to go in the future. And Randall if your still not to sure about how a smart power grid works, it is much like how the internet works, many millions of individual stations all hooked up and working together to create something amazing. Mind you I guess all 1st year physics people could tell you why the internet wouldn’t work also......

Randall Lee Reetz said...


Please give me a single example where knowledge from empirical measurement (Science) has EVER gotten in the way of understanding or progress or invention. How about a single new thing or process that falsifies or has falsified knowledge acquired through Science and measurement.


Randall Lee Reetz said...


You wrote:

"If man had not dreamed and thought about what might be possible then we would still be using stone tools and living in caves. The wheel and every other invention would not have been developed and we would still think the world was flat!"

Which is a bit funny. For one, do you think anyone who ever attempted a measurement ever thought the world was flat? A "flat" world was a popular model not among people seeking truth, but among the masses who have always wanted to believe things without checking first if they are true. The only people who didn't think the world was flat were other freaks who had the same wishful or rhetorical desire to "declare" the shape of the world (how about a cube or a tetrahedron... what tickles your fancy?) and the rare individual that cared more about finding out what shape it was than declaring it so.

Without honest measurement, anyone can say anything about anything. Dreamers have always existed... look at alchemy. But no amount of desire was ever going to turn dirt into gold.

Understanding how nature really works (through measurement) has informed the construction of extremely complex and unstable machines that can under exacting conditions shove protons into or out of atomic nuclei and thus cause one element to become another. But this didn't happen through wishing. This happened through the very very very difficult quieting of desire so that bias is less obstructive to the measurement process.

I really think you do need to revisit your high-school physics materials. This time, don't look at the equations, look instead to the reason science works. Look to the difference between science and everything that was tried before. What is that difference Karrde? Do you know?


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