compressed air vehicles!

I don't believe I saw this possibility mentioned elsewhere in the thread, so forgive me if someone else described it. A hybrid configuration where heat from a small IC engine is put to use might be a way to optimize the range of an air car while minimizing the size of the air tanks. In principle, it should be possible to devise an engine that is essentially an integrated internal combustion and air engine - that is, with conventional fuel injected internal combustion cylinders/pistons along with some cylinders/pistons powered directly by compressed air derived from air tanks. The internal combustion engine really IS a compressed air engine, but it compresses its air on demand with the compression stroke. This takes a lot of the net energy from the power strokes (well, indirectly, but I'm not getting into the thermodynamics here). So, adding a storage tank of compressed air essentially allows one to fuel the car from sources other than petrol (assuming the air is compressed using energy not derived from petrol). However, there is a further opportunity to exploit this configuration. The compressed air adds a tremendous heat sink that can take advantage of the waste heat from the internal combustion side of the engine. The compressed air is sent through a reducer before it moves to the air engine, and this causes a significant drop in temperature. This cool air can take in the heat from the internal combustion engine exhaust thereby generating a much larger volume of compressed air available for use in the air engine. Effectively, one could dramatically increase the capacity of the air tank by taking advantage of this heat that is otherwise wasted. It would be real tricky problem to optimize this process, but a cursory consideration suggests that dramatic increases in fuel economy is possible using this approach.

I'll try to describe a general configuration in more detail to give the reader a picture of what I'm talking about. The most efficient system would harvest all the heat from the combustion process. What heat is not converted to mechanical energy by the internal combustion engine process would have to be transferred to the compressed air somewhere between the reducer off the air tanks and the compressed air engine itself. Suppose the internal combustion cylinders are insulated and cooled with water. The water heated by this process is cooled by transferring its heat to compressed air. Add a radiator after this heat exchanger to cool the water in the case where the compressed air tank is discharged. Now, the compressed air that is now at a higher temperature (and it should be able to harvest a lot of heat in the first heat exchanger because the air is at a low temperature) goes to a second heat exchanger to be heated aggressively by engine exhaust gases. The hot compressed air then goes to the compressed air engine. The temperature of the heated compressed air must be lower than the peak temperature of the engine exhaust gases, therefore the compressed air engine can handle the heat, and should do so without external cooling... so the compressed air engine could be insulated to enhance its performance (less heat lost means more heat for higher air pressure in the engine and more work).

Another interesting implication of this approach is derived from the observation that the energy in compressed air tanks is technically solar energy. The mechanical energy that was used to put the air into the tanks goes to increasing the temperature of the air during the process, and all of this energy is dissipated as heat at the compressor. Therefore, in principle, it's possible to use this energy twice... once as mechanical energy to put the air in the tank, and a second time in some low temperature heating application (perhaps on site water heating or space heating). Perhaps a heat pump can be used to cool the air compressors with the heat transferred elsewhere and harvested at higher temperatures in a condenser to make the process more useful... this might also cool the compressors very well to reduce the mechanical energy consumption required to charge the air tanks. NOTE: I know I'm taking this to an extreme, but I'm really just pointing out a lot of physics that people often miss.

Finally, one might simply add a furnace to a compressed air car to heat the air before it moves to the engine. This would increase the range on the system dramatically while allowing for the use of fuels such as biomass.

It took approximately 20 years from the time VW proved the concept before electronic hybrids were accepted by industry and regulators. The technology for hydraulic hybrids exists now and there is greater incentive for acceptance, given the market acceptance of "hybrids" and the ever increasing costs of electronic battery technology. If Peugeot's efforts are rewarded by the consumer, I think we will see other carmakers following them very quickly.

The true air cars are another matter. I see them finding some success in niche and fringe markets, and among the DIY crowd, but unless Di Pietro's rotary engine can prove itself outside of the warehouse, there is likely a lot more development that needs to take place.

As far as bicycle v. car, in most cases its apples and oranges. Cars are simply an unavoidable reality for most of us for at least some of time, so it behooves us to look for ways of making them more efficient. I think that this technology can be used with bicycles to enlarge their range of usefulness, just as human-electric and human-ICE hybrid bicycles do.

Joe Braxton wrote:

Len Ovens wrote:.... I wonder how much noise they make.

From experience, you will definitely need a muffler. A smallish inner diameter w/ air pressure above, say 50 psi, and no throttle will exhaust at super-sonic speeds.
The ones I've used were for cooling on milling machines, I could freeze ice on the exhaust tube in a 80 degree F shop.

That was my thought too.

I really like the bike though. It is just strange looking enough to make it interesting (old harley rider here) I wonder if just putting coils along the piston shaft path and a magnet on the shaft itself would generate enough power to keep the lights going. Maybe with a super cap instead of a battery. Getting it licenced as a home built motor cycle would be much easier than as a home built car from what I can tell. Might require a battery to be legal. I think the lights have to be able to be on with out the motor running like at lights and stuff... the motor only runs when the bike moves. In fact running a generator off the wheels would probably be better because the the motor would not run at all while coasting. The unit has a lot in common with the old John Deer diesels that only fired once every 4 or so revolutions. Except the piston only moves when fired. A one way clutch lets the bike free wheel other wise.

This same idea could be used in a car by using a flywheel (it could be used without too, but I am guessing the ride might feel jerky - could be the bike is that way too ).

paul wheaton wrote:Somebody sent me this today:

removed video to save space - air powered bicycle

The video is five years old, but still very relevant. I think the way that it projects in bursts is something I have not seen before! Cool!

He mentions that compared to running the same thing on petroleum that the petroleum approach would cost 100 to 200 times more.

Found this one on the same machine:



Not sure but they seem to be testing something... anyway, the feel of the unit is visible. You can see the power and glide feel this would have. Most manufactures would consider this unacceptable. I would feel it was quite worth while for what I would get out of it. The "battery" shouldn't wear out in 5 years like most others. Putting the tanks somewhere not where my feet want to be would be my first change though Simple would be the rule. I might get by with one tank as I travel less than 30KM a day.

As a member of the Bosch Group, Rexroth and Aventics pays particular attention to those initiatives that engage in raising environmental awareness, deal with the question of alternative energy sources and the efficient use of natural resources.It was this spirit that initiated the Rexroth Pneumobile Competition a few years ago. In this creative and innovative competition the participating students have to design and construct compressed air-driven vehicles before putting them through their paces at an event consisting of a number of categories and disciplines. During the course of the design and production process the students gain first-hand experience of pneumatic, that is to say compressed-air technology, while at the same time they become familiar with Rexroth products. On top of all the program presents an ideal opportunity to tighten the co-operation between the Bosch Rexroth companies and the technical universities and colleges in Hungary.

Norbert Esses wrote:

As a member of the Bosch Group, Rexroth and Aventics pays particular attention to those initiatives that engage in raising environmental awareness, deal with the question of alternative energy sources and the efficient use of natural resources.It was this spirit that initiated the Rexroth Pneumobile Competition a few years ago. In this creative and innovative competition the participating students have to design and construct compressed air-driven vehicles before putting them through their paces at an event consisting of a number of categories and disciplines. During the course of the design and production process the students gain first-hand experience of pneumatic, that is to say compressed-air technology, while at the same time they become familiar with Rexroth products. On top of all the program presents an ideal opportunity to tighten the co-operation between the Bosch Rexroth companies and the technical universities and colleges in Hungary.

Thank you for posting that. A further explanation of how it worked would be wonderful My impressions are first that it seems noisy, but it is really hard to tell because of the recording chain characteristics and of course the first vid is recorded from in the car. I noticed on another vid that the noise went away pretty quick when the car was even~15 feet away (though it is hard to judge the back ground noise too).

I noticed the full stroke of the cylinder is not being used. I am guessing that has more to do with using off the shelf parts than anything else. The noise sounds like the crank is moving a lot slower than the cart drive wheel too.

One thing the design points out rather well is how much easier it is to play with these things on a bigger platform of a cart rather than a bicycle. Though the complexity has increased as well. This cart would be legal on the road here (as a bicycle) so long as the top speed was less than 18m/h-30k/h. However I would want something taller for visibility sake I think. The top of my truck hood is higher than that. There are street legal sports cars just as low though.

Of course I can not tell, but there does not seem to be any indication of range/volume of stored air. One of the advantages of using a bicycle as the starting point is the possibility of pedaling home. (this part might be required for street legalness here too.)

The pneumobil is a compressed- air-run vehicle. The energy of air is transformed into kinetic energy by pneumatic cilinders. The first pneumobil was made in 2008 for the competition of Bosch Rexroth Company, wich has been followed by numerous successors.
The making of pneumobiles has became a tradition over the years.

Our team now started first in this competition. So.. this pneumobil not too good YET. We are mechatronics engineer students, this is competition very good for us.
Otherwise, there are other videos too in the playlist:
Pneumobil playlist

Announcement for the competition
http://en.pneumobil.hu/pneumobile_2015/announcement_for_the_competition/announcement_for_competition

The technical specification of task
http://en.pneumobil.hu/content/download/7870/28422/file/3.%20Technical%20specification%20of%20task_2015_en_final.pdf

Bill Mollison talking about compressing air with a trompe

http://www.psa-peugeot-citroen.com/en/automotive-innovation/innovation-by-psa/hybrid-air-engine-full-hybrid-gasoline


Peugeot to launch hybid air air power system . 2015?

The advantage of this system over electric hybrids is that there is a large weight saving . Not having to carry the battery saves power . I wonder if there is a way of charging up the air pressure at home so you always start with a full tank thus saving still more feul .

David

Has anyone seen THIS "revolutionary" (pun intended) rotary air motor for vehicles and countless other uses? I wouldn't surprise if you haven't because it seems to be getting hidden because this design is already like ten years old and I happen to run across it by accident:

The company name is (was?) Engineair from Australia, and inventor's name is Angelo Di Pietro

Here is a proper, excited permaculture attitude being displayed about these very viable replacements for petroleum, electric batteries and all other environmentally "questionable" transportation energy sources: https://www.youtube.com/watch?v=-X6oWZe0QTc

And there are some very simple solutions for GENERATING compressed air as well and I started a new forum topic about it, I call it "windbottling" which makes use of the increasing WEIGHT (mass) of a compressed air tank as part of the inertial energy that allows building higher and higher pressures with "theoretically" the same amount of energy input (E=MC squared, so increase in MASS equals increase in energy). My favorite simplified concept is using the air tank as a pendulum weight and instead of using a rotating compressor head, we simply go directly to the linear back and forth motion of the piston itself, like a bellows which was the first type of air compressor design used in homes and blacksmithing shops, but with a one-way valve and holding tank which becomes "feedback" for the bellows energy input requirement.

The Di Pietro Motor is a 94.5% efficient compressed air motor that can run on energy from sustainable sources such as the sun.

At the moment he uses one size motor for all the applications as seen in this video. With development it has the potential to replace any size motor in any application.

This technology exists today. It's not an engineer's concept bound to a computer screen. It's patented and physically verified. The only thing holding back the widespread application of this technology seems to be will.

Even in light of the gulf oil disaster Obama has been quoted saying "We're not going to transition out of oil next year or 10 years from now" - President Barack Obama, May 26, 2010

Why not Mr Obama? The technology exists right now and your people know it.

For the full article on this motor and more information about other ways we can transition to a post carbon economy see the full article - http://internationalpermaculture.com/2010/06/21/the-di-pietro-compressed-air-motor-alternative-clean-energy-today/

And here is a detailed comparison between the truly inefficient piston design and this new rotary air design:

This would TRULY become a permie-compatible energy solution if these motors could be built from plastics derived from veggie (hemp?) oil via technologies such as 3-D printers. I would imagine there would be nowhere near the amount of heat and stress requirements of an internal combustion cylinder-type of engine or even the piston-type of compressed air vehicles and the "one-size fits all" idea is bound to reduce waste. The rotary design is BRILLIANT because you never have that "top end" sudden stop and reversal of momentum that is required AND you never have that all at once loud release of air at the end of each stroke.

My first attempt at creating this message was rather "over passionate" so I had to reword some things, and in the time between the original post and my editing, I have discovered that the manufacturer's website is no longer in operation, so I'm not sure if it got bought (and shelved?), changed names or what happened, but I thought folks should see that there ARE (or at least were) other options besides the high-pressure designs that the MSM were touting like from Tata Motors and the like.

Namaste,
Brian

Brian,

Di Pietro's company is alive and well, here: http://www.engineair.com.au/

He has found a niche and that may be a two-edged sword. It is never easy to make inroads into an established paradigm. Compressed air is not a panacea (nor is electric, or anything else). There are a number of complexities that would discourage most consumers.

I would like to see how his design works with larger vehicles, loads and steep grades.

It appears that he is looking to smaller vehicles, as he continues to make his engines smaller and lighter. There is a large market in motorcycles/scooters throughout Asia, where they are the principle polluters, after cooking fires.

An efficient air engine makes air batteries more attractive.

Andrew,
Thank you for posting the exact same link I had attempted to access before, but mysteriously would not work for me, and now it does and I hope it will for everyone else as well. It has been quite discouraging for me to know that this technology exists for so many years and to NOT see it being widely publicised as an option IN THE LEAST. It just seems to me to be the ultimate form of not only transportation and utility vehicles but an engine design for EVERYTHING that requires rotation within and around the home because literally, there is no special skill or strength or "minimum income" for people to make use of it. It appears that this engine does not even require the huge amounts of pressure nor "battery capacity" to operate.

How difficult would it be to hinge the entire passenger compartment along with the holding tank to the front bumper and place a piston or two between it and the drive frame and just use the bumps in the road as a recharge mechanism (or just sit and bounce for a few minutes?) that also supplies shock absorption, some simple compressor heads on the wheels for brakes that also recharge the tanks, and even light weight sails, turbines, pendulums, whatever to simply compress air? And as the website states, the air that is expelled ends up being even CLEANER than the air that was collected to power it in the first place!

"Consumer complexities" or intimidation or hesitation or whatever... where, exactly? I mean in comparison to the relatively HIGH maintenance of the vehicles in operation today and the GAZILLIONS of parts required to work in unison just to even BEGIN moving, I just have a difficult time imagining how ANYONE could be intimidated by the practically "Meet the Flintstones" simplicity going on here. I also don't understand what happened to compressed air technology on large vehicles either as I browse some of the designs that have already been in use in mines and other "hazardous" environments, I know they must STILL be in use worldwide for these purposes, but why has it never been offered for consumer use REGARDLESS of efficiency? It seems to me that the OPTION of people becoming totally fuel independent would FAR outweigh the mess, fumes, dangers and hassles of petroleum (and electric) powered options ESPECIALLY in urban areas. It's really difficult for me to restrain my "outrage" over the complete lack of this option, and even worse, the so-called "experts" all attempting to state that "efficiency" has always been the barrier when obviously in the "big picture" perspective this is absolutely not the case if fuel can be obtained and stored absolutely anywhere with absolutely no (legitimate) restrictions.

The "excuses" I have heard just do not seem to add up, these engines need to become "main stream" and pneumatic powered... EVERYTHING should become the next paradigm, in fact, it always should have been this way IMO because the technology has been with us all along, for as long as we have had sails and pendulums, bellows and valves.

Brian,

You need to think it through thoroughly. Recuperative braking will not return all the energy used in acceleration. There will always be losses. Capturing the energy from bumps will never fully compensate for the energy used to get over the bump. Certainly, you can increase efficiencies, but at a point the added gadgetry becomes uneconomical.

One of the complexities in acceptance of air motors is energy density, and, in attempting to increase energy density of compressed air, you increase the energy input as well as the dangers associated with increased pressure. It is one thing to store enough air to accelerate a vehicle to cruising speed, as in a hybrid, but it is altogether different to run a vehicle solely on compressed air. The parameters of use will be very narrow. Fortunately, for Mr. Di Pietro and other air car entrepreneurs, there is still a potentially large market within those narrow parameters.

An inventor wants to see licensing that will compensate for time and effort put into developing the product. No one is going to make a living doing one-offs and prototypes. You need economies of scale. Often (most of the time) thing just don't work out. It may be a travesty, but it is usually not a conspiracy.

Brian Pettit wrote:Andrew,
Thank you for posting the exact same link I had attempted to access before, but mysteriously would not work for me, and now it does and I hope it will for everyone else as well. It has been quite discouraging for me to know that this technology exists for so many years and to NOT see it being widely publicised as an option IN THE LEAST. It just seems to me to be the ultimate form of not only transportation and utility vehicles but an engine design for EVERYTHING that requires rotation within and around the home because literally, there is no special skill or strength or "minimum income" for people to make use of it. It appears that this engine does not even require the huge amounts of pressure nor "battery capacity" to operate.

so far so good. I think an air battery could well be used to power things that need rotation, from food processor to large truck or whatever.

How difficult would it be to hinge the entire passenger compartment along with the holding tank to the front bumper and place a piston or two between it and the drive frame and just use the bumps in the road as a recharge mechanism (or just sit and bounce for a few minutes?) that also supplies shock absorption, some simple compressor heads on the wheels for brakes that also recharge the tanks, and even light weight sails, turbines, pendulums, whatever to simply compress air? And as the website states, the air that is expelled ends up being even CLEANER than the air that was collected to power it in the first place!

No matter how efficient a system is, the people sitting in the vehicle would be better off peddling direct to wheels than to charge some kind of battery. The bicycle is a marvel.

Getting some air from shocks may be possible though. Probably not enough to keep the car going, but to extend range maybe. Braking power would be better used to recharge the electric battery still needed for lights, controls etc.

I understand the article stated that only one PSI was needed to overcome the internal resistance/friction. That is not the same as saying one PSI would be able to do useful work, just that one PSI will make the motor turn with no load attached.

Energy out will still be less than energy in. So while compressing air may be a good way to store and use power from wind or sun or whatever, it is not significantly better than electric on straight efficiency. It is not better than electric so far as moving parts go either, in fact electric can have fewer parts. Electric is quieter. Electric is easy to sell because it is what people are used to and they know they have electric power to their house already. So electric is better? No, but just easier to sell.

Is air better? I would suggest the big plus with air is that the battery takes less energy to create, less rare materials. I suspect it would have a greater number of cycles and does not require specialized equipment to build, or at least not as specialized as lithium batteries for example. The efficiency for even a low complexity air battery is high, but lithium cells require complex circuits to ensure they charge right and most need a capacitor bank to ensure peek currents. NiCd Batteries would seem to be about the best in this case... I'm talking flooded NiCd BTW. Recycling all the bits in an air system is easier to do as well... in fact there are bone yards of steel ships just waiting to be harvested

The problem becomes charging, yes air pressure can come from solar or wind and there are newer very efficient compressors, but what will happen, is that air pressure will come from coal powered hydro where the transmission loss alone may be 90%. The compressor will be whatever the service station's normal supplier is selling.

Should this stop air powered from being used? No. The only way to change things though is to start using an air car or tractor or whatever, powered from your own source of air.

Arrgh, alas, could not edit my latest entry, here be what I woulda shoulda posted Fortunately, it seems many arguments are largely unfounded and untested and if I'm not mistaken, a bit over-reactive as if the notion sounds a bit threatening to an individual's livelihood, which is understandable if these concepts can be allowed to "pan out".
If indeed a 3-D rendering could be obtained for mass production and even scaling on 3-D printers for this engine, I really really don't see a whole lot of "apprehension" going on for entrepreneurs to just start pumping out low-pressure pneumatic "gizmos" at an even more lucrative pace than personal electronic devices. If I wuz DiPietro, I'd just release it for free and even help the world start to DIY just to watch the whole Military Industrial Complex fall flat on its... virtues (must remember the monitoring).

Seriously though, it wouldn't be long before very few metallic ores were needed for much of anything as everything became made from plant-derived plastics, it appears DiPietro's use of aluminun is likely over-kill, and Henry Ford himself demonstrated how much more superior HEMP fibers are to steel, and that's just cars, so imagine how light EVERYTHING could get while becoming STRONGER and more flexible and longer lasting, and ZERO LUBRICANTS required as we design new cars, trucks, aircraft, ships, buildings, bridges and ALL of their infrastructures running on nothing but compressed air... except for some "teensy" almost insignificant electronics that could easily go fibre optic or even sonic controlled through comm tube conduits instead of heavy, bulky failure-prone wires and continuously oxidizing metals... opportunities are mind boggling and not the least bit far-fetched IF the technology were ever allowed to make a PROPER début.

Wow LOVE the enthusiasm and debate that's opening up and I really hope my heavy "biases" and overzealousness doesn;t yet again become my downfall, but I really AM hoping to get input as well as some mutual participation/testing of some pretty easy to prove concepts if this is indeed valid.

I mentioned the design for the car to include the passenger weight AND the air storage tanks as part of the shock absorption BECAUSE compressed air gains MASS. So in effect, (in theory) the vehicle is converting the mass of the load into ENERGY whenever the vehicle travels in any "unintended" direction, and I'm sure there are multi-stage almost friction-free compressor devices that could be incorporated into the braking. Again, we're talking about the future of 3-D printed and/or extruded bioplastics and fibers and resins and stuff that can even potentially virtually eliminate hoses and all kinds of loose parts if designed intelligently instead of always catering to specific commodity markets for resources.

BUT in the mean time, it's becoming extremely interesting to watch people get creative with all the stuff that's already "out there" to be re purposed like using old small gas engines as air compressors and such, and just "vessels" to hold air here and there... I think it's a grand strategy personally. Seems everyone HAS air tools and such, we just don't make proper (or full) use of them. I dunno, I have fun learning things as I break my tools at least, LOL

Brian,

Compressed air is not free energy, nor is it necessarily clean energy. It takes a lot of compressed air to move a full-sized car with a full load. It takes even more to move that car and its load up a hill (electric has similar problems). The energy you might glean from braking and bouncing will help, but you will still need a lot of external power input.

As Len pointed out, one bar may be sufficient to overcome internal friction, but it doesn't do any work.

With air tools it doesn't matter how big a tank you have, once you go below minimum useful pressure, the compressor needs to cycle. Depending on the tool, that minimum pressure can often be close to the tank's maximum. Compressed air is heavy and bulky. You will have to carry a lot of dead weight to maintain useful pressure.

Air lines and valves can ice up. Not fun.

All the things I have mentioned here and previously, as well as those I have not, can be remedied -- at a cost.

Simple pneumatic systems are not efficient. For them to be efficient requires complex and costly technology.

As I wrote before, an air car can be successful within limited parameters. It could compete with petroleum and electric, within those parameters. The potential market is still quite large, within those parameters.

Inventors have to eat. Di Pietro deserves to make a good living from his work. He might sell you an engine, but a one-off would be expensive. He might sell you plans, but it would be expensive to fabricate. The 3D printer would probably not give you the tolerances needed without some machining, assuming the material meets specifications. You will likely have to wait until someone begins mass producing them.

Forgive me if I'm not following "protocol" for message exchanges here, but I just wanted to add that i was recently ELATED to be able go through some of the detailed images and design diagrams of the compressed air locomotives and learn how REHEATERS and recycling of expelled air had been designed into these engines and that concept is TOTALLY IGNORED in the use of air tools today. The exhaust is completely WASTED and is the actual cause of the low efficiency, we WANTONLY waste the air exhaust and don't even attempt to recycle it.

I have a YouTube video of a device I began working on that uses a flywheel (old RV spare tire) to assist in rotation of a gasoline-powered electric generator converted to run on COMPRESSED AIR and part of my design was to COLLECT the exhaust and feed it back into a compressor head powered by the same flywheel inertial energy. This feedback mechanism virtually NEGATES the "freezing up" so-called "givens" of compressed air usage and I was DELIGHTED to observe that this compensation had ALREADY been accounted for far before I had even considered this obvious loss in efficiency.

Another concept I am attempting to revitalise is the use of STAGES of compression that push "higher than ambient" pressures into the intake of compressors through various "symbiotic" means for higher throughput AND less work because higher input pressures actually help to AID the compression strokes to the point of compressors acting as part engine, part compressor which was WIDELY being researched and developed prior to the "petroleum influences" that seduced the market place with terms like "more bang for the buck" as if "the buck" was ALWAYS some sort of "given" when it comes to issues of power generation and usage. And that "seduction" is the very crux of the issue because we have been slowly and deliberately "swayed" into believing that we all are "powerless" without the use of the fake "place-holders" of paper and digital currencies.

A YouTube link to my "conceptual" design for utilizing compressed air to power already existing (probably uber-inefficient) gasoline-fired internal combustion A/C generators. I didn't even try to explain the exhaust recirculation "plan" that uses the two-cylinder compressor head that moves in and out on demand to absorb the exhaust and recirculate it into the source, except in some text added later on... "proof of concept" is still sitting in it's original state, a ball valve on a spring instead of the "trigger" mechanism and some reworking of the "ramp" would likely solve some of the issues, but as i stated, this is an EXTREMELY PRIMITIVE demo.. right down to my gross "Flintstonesque" Buddha belly beer gut prominence LOL. https://www.youtube.com/watch?v=5EiipS6X6hs

Brian Pettit wrote:
(E=MC squared, so increase in MASS equals increase in energy).

The Di Pietro Motor is a 94.5% efficient compressed air motor that can run on energy from sustainable sources such as the sun.
Brian

For people following this thread, the Equation E=mc^2 is for nuclear conversion of matter to energy (ie nuclear bombs or nuclear reactors). It is not applicable to compressed air vehicles.

Having taken three years of college thermodynamics and worked in industry, I have rarely seen any human device achieve a overall efficiency of more than 50% energy conversion.

Well said, Brett. Two thumbs up.

I can remember Bill Mollison talking about a method of storing compressed air in his PDC lectures (http://www.powells.com/book/permaculture-design-course-13-disc-dvd-set-1110000041488)
He mentioned using a trickling stream flowing over a number of tubes and that somehow pushes air into a compressed air chamber. Oh.. I just found it as I was typing this!
The Trompe/Trombe - http://tcpermaculture.blogspot.com/2012/11/the-trompe-almost-forgotten-air.html


A free source for those of you with running water!

and then I just scrolled up and saw Paul Wheaton's post... OK

Anyone else watch the Mollison PDC where he goes on a long rant about compressed air as a solution to make transportation and work more simple? I forgot what he called the set up but basically the compressed air comes from moving water over a air well type thingy. Been a few year since Ive seen it but if it is actually pratical in some areas then at least some the population could have a "free" fuel source for these neat cars.

I have been thinking about it for a pneumatic robot.
Only one problem: The energy density is about 1/8th compared to a Li-Ion battery, and that is for air at 200 bar or 2900 psi.
So not too bad if the energy can be used without converting it into electrical energy first and not the highest energy density is required.

Have you looked at materials that "adsorb" the air, like "zeolite"?  

Check my numbers but at first glance a much more reasonable pressure of 300 psi appears to store 9 Wh/kg (weight of zeolite only).  (compare to 20 Wh/kg Nickel-Iron or lead-acid, ~150 Wh/kg Li-ion batteries.)

Zeolite costs maybe ~ $1/kg ?

Even this is usually considered too heavy for transportation, but it looks interesting for solar-storage, grid or off-grid-storage.  

Brandon, yes I did watch that particular Mollison rant, lol.  I think Mollison's right, it does make a lot of sense, especially if you have a source of hydropower.  The water provides cooling during compression and the resulting "isothermal compression" is more efficient.   It's probably vastly easier to use modern pipes than to tunnel deep shafts out of solid rock.  It's a nice way of getting refrigeration and air conditioning which is otherwise rather difficult to do.  I think the energy storage application for transportation is limited, except maybe for going short distances on something like a tractor where low energy density might be less of a problem.