Is this a plausible engine design?

Pre-heating the air is not new. GM has been doing this since 1980 (at least in Canada) It only gives a 5% increase in efficiency. It is most effective in cold weather environments. They started with an electric carburetor heater and later added heat from the exhaust manifold.

In general the heat gained by compression would be cancelled out by the decompression cycle.

The only gain would be from the extra compression and heat due to the combustion. What is to stop the combustion pressure from feeding back to the compressor and stopping or reversing it?

The other gain is the decrease in moving parts and decrease in weight which is always good for reliability and efficiency.

The only difference between this and the rotary engine is the volume of gas.

If you want to increase volume; burn a liquid or solid instead of compressing a gas. Now that brings us back to a rocket engine.

Hello double_j_b

Thanks for the web-link, but I wouldn't be getting excited about the developments there.

<"...November 21, 2006 StarRotor receives its fourth customer.

StarRotor will design and build a specialized 18-hp ethanol compressor.....">

So as far as I can see, that Company is rather dead-in-the-water.

They are "having a difficult time" because their product is not as good as hoped for, are under-capitalised, and/or are not market savvy.

Kind Regards....

Yeah they seem to stall out a couple of years ago I have maintained contact with them on occasion but the last time I sent something to them they did not respond.

I volunteered for testing of the motor when they had it ready as i have about a 120 mile round trip drive to and from work every day. They were really intrigued in my abilities at the time and according to them were looking forward to having me test it for them.

Now I know what your thinking, how much were they going to charge me for this privilege. The answer was nothing. All they wanted was for me to track mileage and maintenance for a year. But alas nothing has arisen from this and now I fear they are as you say "Dead in the water".

My main interest is the feasibility of the design though and I figured all the Physicists and engineers that we have on this site that we might be able to decipher the concept and possibly stir some interest in it again.

It would be great to be in on the ground floor of something like this as a break through in transportation. If indeed thats what it is.

Thanks for the response guys hope to see more from the rest.

"It would be great to be in on the ground floor of something like this as a break through in transportation. If indeed thats what it is."

Yes, it would. And nearly as great to debunk this if it is bunkum. That, of course, would leave it to be merely 'um'. I shall follow this thread with great enthusiasm.

The engine is a design by a colleague of mine. This thread is correct about the company being undercapitalized. It would be worth a look at the patents for those who are seriously interested. The thermodynamic claims remain true. The primary manufacturing problem is similar to, but distinct from, that of the Wankel engine -- efficiency depends on the tip seal. Conceptually, the tip seal was to have been a small gap in the range of 0.1 to 1 mil. That requires very careful machining tolerances followed, in operation, by careful temperature matching of the two primary rotating parts.

With that knowledge in hand folks, do not forget that any other concept using a compressor, a combustor, and an expander with the same pressure ratios would produce the same thermodynamic efficiency. (and is covered by the patents, so some sort of licensing is required). See

http://www.starrotor.com/Engine.htm

for discussion of the Brayton Cycle as it pertains to the Starrotor. Note that drawing on the lower left side of the page. It has compressor, continuous flame combustor, expander and recuperator. Note also that the compressor can use liquid injection to reduce the work of compression from adiabatic to isothermal. Let your creative juices run ... perhaps now is the time to try the Brayton Cycle in land based automotive vehicles.

By the way, if you know of a means to engineer a low friction sliding seal that could work on the tips of the inner rotor, I am sure the Starrotor team would love to collaborate with you.

In terms of full disclosure, I am a colleague ... I have no financial interest in Starrotor or in any of its patents ... I am merely an outside observer who is impressed with creativity in engineering design.

Damn, I knew I should have delved further into them and wondered why they had yet to return my phone call. (Ref this post - http://cr4.globalspec.com/comment/193497/Re-More-About-Compressed-Air). If any of you have any alternatives to this engine (that will run off compressed air) I'd appreciate you're imput.

I'm not familiar with the part you're talking about, but I'm assuming it's an expansion, machining tolerance and heat tolerance problem. I may not be an engineer, but I am a thinker (ok, so that's still a moot point, but I digress). If you still have contact with your collegue, you might want to suggest something like a machineable ceramic. I'm not completely familiar with all or the properties of these types of materials, but it would seem to me to, at least, minimize the issues they are having with it

Here's a link to what I am talking about http://www.mcmaster.com/param/asp/PSearch2.asp?reqTyp=parametric&act=psearch&FAM=ceramic&FT_101=113131&session=ceramic;101=113131&sesnextrep=925346483858953&ScreenWidth=1440&McMMainWidth=1025

It seems to be prefired, and they claim it can handle machining. I don't have any idea to what tolerances, but I'm sure there is some substance that will perform to the tolerances they need. This isn't rocket science. With the design confirmed, it's just a matter of finessing the little parts.

Give it to them for free, but you can mention my name and let them know I want a crack at that engine...It's the best I've found for my master plan (Yes, Pinky, we're going to take over the world). I've found another based on the Wankel design

http://quasiturbine.promci.qc.ca/EProductQT600SCPneumatic.htm

but I have more trust in the Engineair model (gut feeling, I couldn't put it into words right now). I'd like to know if you're talking to him at all or can get in touch with him.

Research via Google under Brown's gas.

I met Dr. Brown...20 years ago......system works but on a very limited volume...ok for precise tiny welding torch ON THIN METALS but producing machine uses more energy than created available gas energy produced.

Applicable to an automotive engine?...not yet...violates the laws of physics.

Or we have to find a way to re write those laws...............

MR. GUY

Gerotor pumps have been used for eons as oil pumps in automotive engines. In such an application, their limitations are minimal: if they pump inefficiently, the leaking oil serves to lubricate the rotor and gear, and the hp consumed is infinitesimally low vs the engine hp.

I think many people with an interest in engines and hydraulics have toyed with the idea of making an engine out of a gerotor pump or two. I certainly have, and I've also followed the Wankel from its first automotive use in the NSU. The Wankel is no more efficient than a piston engine, (in terms of BFSC) and, in fact, even in the early days there were few claims that it would be more fuel efficient, at least by people with an understanding of engines. It (the Wankel) is compact, relatively smooth running, and has fewer parts that a piston engine of comparable horsepower -- but fuel efficiency is not its strong suit.

I haven't been able to find anything to suggest that this engine would offer the same efficiency (on a BSFC basis) as a Wankel or piston engine. The crankshaft journals of a piston engine are small and low friction, as compared to the outer surface of a large rotor. The quasi-hemispherical combustion chamber of a piston engine is heat efficient (low surface area to volume), whereas the compression and expansion areas of this engine are high surface area. Jet engines are not efficient as compared to piston engines, even at the very high compression ratios of modern jets, which promote efficiency. At just 6:1, the compression and expansion ratios for this engine seem too low for efficiency.

They claim that there is no contact between "the rotors" (by which I assume they mean the inner and outer rotors -- not the compressor and expander rotors). The expander drives the compressor: at some point there needs to be contact to transfer motion. They do not explain how motion transfer without contact is possible. Typically the inner rotor must drive the outer rotor. In an oil pump, there is little or no metal-to-metal contact, because of the oil film strength. (Perhaps the inner and outer rotors are held in perfect synch by high precision gears not shown? If so, the gears will operate with friction.)

Although they assert that the engine should be 2-3 times as efficient as a piston engine, they produce nothing to support that contention, and there seem to be formidable challenges. How can they keep the housing round, given the constant heat input to one location? How can they prevent oil breakdown near that single location? Why is 6:1 seen as sufficient when modern jets operate at much higher pressure ratios? Tip and side losses have been major challenges for the Wankel -- why not here, too?

From what I have been able to read about this engine, I'd expect it to be somewhat lower in efficiency than a piston engine, and even slightly lower than a Wankel engine. Perhaps that is not really the case, but I see nothing in their site that would lead me to think otherwise.

If they can get it to work in an application (like cogeneration) where waste heat could be used productively, then its advantages in smooth running and low exhaust noise might make it attractive.

Ok now I am in no way an expert on thermodynamics or even how this engine should work.

JCROCK seems to have a bit of inside information on the designs and such. And not that I am trying to pit anyone against the other, but when you are referring to BFSC i have no idea what you are talking about.

Efficiency of the engine appears to be based on the ability to create a "Better Burn" not so much on what you are referring as to as friction problems. I am sure this would be a design, that since it has such close tolerances, would require the use of synthetic oils. Clearances would have to be set and maintained by shimming and precision bearings. with these being flooded with synthetic oils friction could be minimized.

Jets are not efficient because of the massive amount of fuel that has to run through them in order to create the force needed for thrust. The compression in the Starroter design starts with the pre-combustion heater and then appears to be magnified by the rotor design.

Granted anything that is generating and using that heat to regenerate more heat seems as though it would be creating its own problems. You would have to have some kind of way of regulating the temperature within a degree or less to maintain the tolerances requires to stabilize the combustion chamber. However I think this can be accomplished with a refrigerated cooling system circulating through the oil and block.

I believe this would also help in maintaining roundness of the rotor housings and oil breakdown.

The main thing that still confuses me is how you will start the thing. It seems to me that you would need something to spin the motor up to at least 2000-3000 rpm just to get the cycle started. Again I have no idea about this as the cycling is still a bit mysterious to me.

As I said at the beginning of this reply "I am in no way an expert on thermodynamics" so everything I have put in here I am sure will be contested. So fire away and lets see if we can get some additional input from some of the other Braniacs in here.

Blink and double jb both make very valid comments. First the thermodynamic efficiency is monotonic with with the pressure ratio [or temperature ratio], so the demonstrated 3:1 and projected 6:1 do not support the efficiency claims. Get it up to 15 or 20 to 1 and this engine would sizzle. Tip seals and side seals remain problematic. The higher ratios probably will require two stage compressors and two stage expanders [or maybe even three of each].

As for contact between the compressor section and the expander section. There is a shaft between the expander and the compressor, as in a turbine, so some of the shaft power is consumed by the compressor and the rest is available on an output shaft. With no reciprocating parts, the engine is a minimum vibration engine.

As for starting, the shaft could be driven by an electric starter motor as is common in automotive engines or a compressed air storage bottle could start the engine through the expander, with or without preheat through the combustor.

Two moving parts are the inner and outer gear rotors, each with their own center of rotation, and each with pure rotary motion. They must be synchornized to achieve the desired small gap and to maintain it through a full cycle, so there is a zero backlash gear system to maintain synchronization.

Yes, there is a temperature gradient around the perimeter of both the compressor and expander and yes, that has led to manufacturing challenges. Manufacturing would be much easier if we had materials with zero thermal expansion coefficients over the working temperature range. Note that all teeth go througha full pressure swing cycle during each revolution so they are all in an oscillating temperature environment.

The conceptual design has no sliding friction. However, my instinct is that with small gaps, the working viscosity of air and of combustion products will create a fluid dynamic drag that would reduce efficiency compared with the friction free point design.

The theory is sound ... the Brayton Cyucle works for axial flow turbines in aircraft, in ships and in power plants. As I mentioned in my last post, this may not be the only geometry that would work. The Starrotor team is still trying to overcome the manufacturing challenges ... an observation that would not surprise anyone who has ever gotten close to an engine technology to replace the reciprocating otto and diesel cycle engines used today.

One final note. I understand that the starrotor geometry is the subject of one of the patents. The involute shape, as I understood Mark Holzapple, is unique and designed to keep a single point of near contact between teeth during a full revolution. Watch the animations very carefully and you may see what I mean. I do not know if earlier oil pump designs used the same geometry ... I doubt it, because the design team found they could not machine it with conventional machine tools ... they had to obtain a NC mill to do it to necessary tolerances.

There are substantial manufacturing challenges, but the payoff, if successful, is almost too much to estimate.

This thread poses a question that I recall as "Is this engine for real?" The answer is the concept is for real. The compressor and the expander have been sold to customers as stand alone units. The full engine has either not been tested or test data has not been released to the public, yet.

Once again, I challenge all the bright mechanical designers out there to offer solutions to make this or a similar concept feasible. One similar concept would be a swash plate drive with axial pistons and variable compression by means of the angle between the swash plate and the drive shaft. I hear this has been used in some torpedos. Lots of parts, but proven ring technology for sealing between pistons and their cylinders. I know, I know ... why not just burn the fuel in the compressed air and let it expand against the same piston, instead of another piston. The difference is the quality of the combustion and the ease with which it can be ominvorous [meaning multiple fuel types] with external combustors.

Happy New Year All!

In an ordinary gerotor oil pump, the inner rotor drives the outer rotor through a contact patch that "rolls" and skids around the "points" of the inner rotor. Driving one from the other via zero backlash gearing would reduce peripheral friction, but substitute gear mesh friction -- a good trade, I'd think, if the gears can be 1. zero backlash 2. stable in diameter, 3. round while operating. Such gears are not inexpensive to create. It seems that the gear on the outer rotor would need to be rather large, suggesting thermal challenges. Maintaining true zero backlash (not simply the compliant noise-reduction type of zero backlash gearing) in heavily loaded gears without causing noticeable binding somewhere in the thermal cycle would be difficult. You could permit some backlash, but then clearances would have to increase to prevent contact between inner and outer rotators.

The conceptual design has no sliding friction.

Sort of. You'd have to ignore gear mesh friction. Teeth slide in and out of mesh under great pressure. Also, the rotors would have to be supported on rolling element bearings, adding to cost.

The theory is sound ... the Brayton Cyucle works for axial flow turbines in aircraft, in ships and in power plants.

The theory is sound in the sense that such an engine can be made to run. However, I can see no reason to think that this engine would be more efficient thermally than any of the competing engines. Jet engines are no more efficient than piston engines and powerplant turbines are more efficient than a diesel only if cogeneration is used. If anything, I'd think a jet engine would have an advantage over this, because of the straighter flow path. So as this stands right now, at 3:1 expansion ratio, I'd expect very low efficiency. I don't think efficiency would get up to diesel standards until pressure ratios were around 15:1. But even that is if everything else has been optimized... and there are a great many "everything elses": sealing without incurring friction, the mechanical challenges mentioned, the surface area exposed to heat, and the means to keep heat from going off as waste, etc.

Given that a thoroughly developed and expensive GE LM 600 turboshaft has 42% efficiency using a Brayton cycle, the 45-60% claims seem far too high. Large engines tend to be more efficient so a scaled down GE would be no better than a VW TDI diesel, at 41%. Perhaps, with enough development, the Starrotor would be in the same region.

I do not know if earlier oil pump designs used the same geometry ... I doubt it, because the design team found they could not machine it with conventional machine tools

Earlier designs also did this trick -- in fact, the name gerotor comes from GEnerated ROTOR where the path of the inner rotor generator the shape of the outer rotor -- specialized tools had to be used. There is also the Geroler (a trade mark of Eaton, I think) in which there are rollers between the elements, providing very effective sealing and low friction: costly but efficient.

I hope your colleagues can get their engine working efficiently and reliably -- I'd love to see something new on the market.

I like the term omniverous!

I agree that the answer to the basic question is, yes, its the real deal... but there's a lot of development yet to do, and the efficiency is not likely to be any better than a VW TDI initially, and perhaps for a long time to come. But I suppose no one said this would be easy. After all, even the easy stuff (six cycle mods of existing engines, for example) can be hard.

We have kept this dialogue on technical issues ... and I am grateful, as some drift rapidly away from those issues.

If the design team can make their concept work, I would expect their engine to be much less massive than the VW diesel.

Re omnivorous fuel. I have lost track of it, but there was a very promising ceramic combustor that came out of a University In PA some years back. As I recall it started as a ceramic tube. Air passed through it. In the middle (approximately) there was provision for fuel injection and ignition. Once established, the fireball stayed put and local heating of the ceramic provided sufficient IR radiation to assure continued combustion in that location so long as air and fuel were supplied. Lean burn was stable. I never knew if they used the acoustic principles of the Lennox pulse furnace using a resonant tube to create compression waves that compress the fuel air mixture at the desired flame point.

The opportunity to use this sort of combustor is the primary engineering advantage I forsee for a Brayton cycle engine.

We all know that beating current engine technology with a new geometry is fraught with manufacturing challenges. Like you, I wish the Starrotor team well.

Howdy again, from Aggie Land,

double i b wrote

"They claim to be able "theoretically" to double the efficiency over a standard piston engine. I am curious as to validity of their claim and am hoping that some of the BIG BRAINS in here could possible clear up some of the workings of the engine. ... Please look this over guys and let me know your honest opinions."

Since my last post I have exchanged emails with Mark Holtzapple, the inventor and enthusiastic lecturer on the Starrotor concept. His company is progressing with contracts from clients needing compressors and expanders. They have the engine development on the back burner for now. Expect some new posts in the news section of their website in the next few months.

Re the thermodynamic efficiency. The Brayton cycle does produce the claimed efficiency when the pressure ratios and temperature ratios are high enough. There is no magic here in the theory ... The Carnot limit is not exceeded. To approach Carnot efficiency in any heat engine, one must carefully control internal friction and pumping losses and create a flow pattern and thermal energy addition pattern as close to thermodynamically reversible as possible. The reciprocating action and pulsed combustion characteristic of piston cylinder based engine technology is distinctly Irreversible.

Continuous flow concepts are closer to reversible. Among others, three engine concepts achieve this to varying degrees: axial flow gas turbine, the Wankel engine and the proposed Starrotor Geometry. The Freedom motor embodiment of the wankiel engine has most recently been developed by Moller and its engineering history is well documented on the web, http://www.moller.com/files/fm_ancest.pdf .

The axial flow gas turbine and the freedom engine are well along in their engineering development life cycle and can both be purchased today. The Starrotor development is at an earlier point in its lifecycle.

The history of the wankel engine is illuminating ... a prototype demonstrated not later than the early 1950s ... tentative commercial application in ~ 1965, automobile application in mass production apparently about to emerge 60 years later. In between it saw service in small vehicles and in the 1970s it started to see service in specialty automobiles from Mazda.

As I recall it, the Corvair engine from GM took tens of millions of development and testing person-hours before it reached the maturity sufficient for marketing it. Likewise the Northstar engine.

Patience and capital are required for every major engineering breakthrough. We are talking about several teams who are leading the way. I remain a fascinated observer of this exciting process.

HAVE FUN

JC Rock

Love the comments and nice to know the company hasn't given up on the design. Since you're in contact with them, and you either direct me to them or pass this. The stumbling block seems to be a precision part that has very little theeermodynamic change and is machinable to exacting tolerances. I don't know crap. It's an honest evaluation, but I'm forging well informed (probably a neurosis, but I'm just saying...).

I know of several types of machineable ceramic composits that are prefired (no shrinkage), and can handle serious temperature differentals without expansion or contraction problems. I dont know the science behind them, but I know that they exist. And, wow, I was pointed to them by another member here. so damn, it's not even my intelligence (though I have always been proud of being smarter than the average....barnacle).

I'm looking for a pnematic engine. I want a good one. There are only two prototypes I'm aware of, one is the starrotor, the other is an actuall working prototype based on a wankle configuration (out of Quebec, so you can understand that I'm a tad more reluctant to deal with the quasi french than even the French, but I'll do it, I swear, I will condemn my soul to make this happpen....am I ranting? Damn, more pills...mmmmm pills.

Prof Mark Holtzapple teaches in the Chemical Engineering Department at Texas A&M University, College Station TX.

The faculty directory for that department is on the web:

http://www.che.tamu.edu/people/faculty

HAVE FUN

Thanks dude, time to badger a Prof. Don't worry, I won't mention you unless things go well. If they don't, I know where to bury the evidence <evil grin>

A FRENCH company developped an air driven car which will be shortly in series production.

names, names, I need names (mmmm brains...but I digress)

Re Compressed Air Storage, there is a lot of useful insight available:

http://www.theaircar.com/acf/air-cars/energy-storage.html

http://www.theaircar.com/acf/air-cars/compressed-air-history.html

http://www.gizmag.com/go/3523/

Note that the alleged production ready compressed air auto uses a continuous combustor to heat the compressed air before it is expanded. I think you would find that very beneficial in your dream system.

HAVE FUN

PS I get enough spam already!!!!!

Sorry to disappoint you but both the links you listed lead to non-starters. Both are deader than the starrotor company (which is teetering as we speak).

I really want a capable air powered car, for purely selfish reasons. When you drive 150k+miles a year, you'll take any minimization. But, in truth, I am only looking for a compressed air engine to run a generator for a fixed location application. I want it to be able to generate power for a home or complex when primary sources are not producing.

And when the primary sources are not producing, and you have run out of compressed air, you can always pump that compressed air tank, with your trusty bicycle pump.

Replying to Comment by tomkaighin: "But, in truth, I am only looking for a compressed air engine to run a generator for a fixed location application. I want it to be able to generate power for a home or complex when primary sources are not producing."

Well here is one site that does have a compressed air motor that is in low volume production. Company is apparently in about the same stage as the Starrotor Company. The Engineair expander has similar size as a Starrotor expander, but uses sliding seals instead of precision clearances.

http://www.engineair.com.au/development.htm

If you wanted to use a hydraulic motor as a pump/motor and compress your storage gas with the hydraulic motor, we are back to the swachplate axial piston motor:

http://www.oilgear.com/file-bin/motors/bul_56015a.pdf

This has been manufactured for decades so infant mortality problems are less likely than with other technologies.

Sorry about the nonstarter comment. I visited the sites. Yep, lots of information there, I just meant to say the companies and development appear to be non-starts. Or at least leading off into a direction that doesn't include an air powered engine.

Starrotor, while I wish them luck as well, is just another variation on an IC engine. Just not what I was looking for. Oilgear I'm still looking at. And believe me, there are lots of considerations I don't have the experience or knowledge of, the problems of compression and expansion of a humidified product being one of them. But I am starting to make some headway into bowels of Air Liquide, AirGas and Air Products (those are the big 3 I paint tanks for) and am hoping to pick practical brains there as well.

I'm not completely tied to compressed air either. It's just that it's prevalent, relatively inert, requires no other process to create or refine and has been in use long enough to have most the kinks, if not completely worked out, at least identified.

Your list of companies whose brains you will pick is wonderful. Those engineers and technicians make their living compressing air and distilling it into its components.

Look at what is working for off peak energy storage:

Hydro (I understand water is pumped uphill at Niagra Falls at night, to be released through the turbines the next day)

Battery (think toyota prius with its 3 mile electric only range)

Flywheel (not fully available at retail)

Compressed air (~ 15% of what you store, you get back ... unless storage is insulated, air is kept hot and lost heat is replaced during expansion)

Capacitor (used for pulsed power, but not much else, although super-capacitors are starting to appear as power boosters in battery electric systems)

Inductor or Electric Coil (also used for pulsed power and not much else)

Hot oil (used in a Spanish Solar Power plant to store heat needed to make steam at night, planned for an Arizona or New Mexico solar power installation)

Mechanical Spring (wind up toys, cross bow, etc)

Hydrogen (make it with electrolysis of water, the burn it or push it through a fuel cell when power is needed)

Metals (purify sodium during peak power periods ... add water to make NaOH and steam when you need the steam ... but add water carefully, because explosions are common)

Ni-Fe battery (the nickel iron battery is used for energy storage in large industrial settings where its unstable chemistry can be carefully supervised and controlled)

Bottom line is that right now, compressed air and hydro storage are used for medium power temporary sources. Chemical sources remain the champs ... hydrogen with a reversible fuel cell would be wonderful, works in space and other high budget environments, but not yet for the rest of us.

All of the chemical storage schemes are expensive and have a finite life. Compressed air, for all of its inefficiencies has an unlimited cycle life unless you let the pressure vessels corrode, crystalize or all the other things you must see in your day to day job.

Yep. Lots of interesting implementations, none of them perfect. I got in touch with Mark Hotzapple who was wonderful enough to respond very promptly and inform me that I had screwed up companies (I have been looking at Engineair and Starrotor and contacted him as a principle for Engineair...Chagrin). I think I covered well and he did get me the contact info for one of the reps there that could answer my questions - hopefully).

All of your listed energy storage devices seemed like meritable ideas except for the pumping of water up Niagara falls...seems to me like a hydrodynamic version of pissing into a monsoon as far as energy transfer is concerned. I don't think I want that kind of return on a redneck shower. But, when the energy is available free for harvest, efficiency is much less of a concern as long as there is a net gain in productivity.

I've been looking at the hot oil/hot salts storage that are mostly considered for solar capture storage alternatives. Interesting and stable devices but still need a thermal/mechanical device to harvest. Usually the temperatures able to be stored are not in the order of magnitude to generate power conventionally (steam turbines), without excessive inefficiency.

I'd like to know where you got the 15% number for air compression/recuperation. I'm not disputing it, I just don't really know that much about it. The issues you mentioned are becoming clearer to me, with the temperature exhausted compressing a gas and the heat required for re-expansion. I know the concepts, but not the working problematics. I was kinda hoping a buried tank could use the surrounding ground as a heat sync for both storage and recovery as the sheer mass and insulating properties might give some pretty decent results, but liquid salts or oils could do better (though add to the system cost).

Hydrogen I am very familiar with. The main problems are generation losses, reconversion losses, PEM costs and volatility. Price a 5kw PEM hydrogen generator. It's exorbitant. It's also a heavy cost catalytic process. Ballard was supposed to reveal the results of tests on a 750kw generator 5 years ago, but that failed to come to fruition. I still like hydrogen, but the return capabilities are as of yet not there. It has the added drawback of being much more explosive than natural gas. On it's good side is that it is about 30 times less dense than natural gas and dissipates into the atmosphere incredibly fast.

Keep the thoughts coming though. I'm not tied to compressed air, but batteries are a long way off in terms of economic feasibility.

And don't laugh too much about tank corrosion. I was power washing an oxygen sphere (1500 gal, approx 14' diameter). As the water hit corroded areas, I noticed some pits that were in excess of 1/2 in deep. I called, thinking he shell was probably no more than 3/4 in. I was right, but the outer shell is just a vacuum shell protecting the internal pressure vessel and providing for a vacuum ( only vaguely understand the reasons) but suffice it to say, if the outer shell breaches...no big deal, they just come in and replace the tank. The internal shell is designed to hold the pressure, but the heat transfer that is created just screws up delivery, but does not cause explosive decompression issues normally. (mechanical rupturing can, but something would have to go through both the outer shell and the internal containment vessel).

Keep up the good work, and if you know any more about the ins and outs of compressed air storage, let me know. Hell, if you think of another way to store excess power, let me know.

OK. I Looked at the Aptera web site. 300 mpg will NOT happen, even or especially in that 850 pound vehicle.

Add 100 lbs of diesel fuel 4 passenger and baggage, you have a drive off weight of 1500 to 2000 lbs. The best efficiency we could hope to achieve right now in storing and retrieving energy is about 60%. No one is anywhere near that in a full system.

Engineering moves by evolution, not revolution, in most cases. The Aptera minimizes aerodynamic drag, has streamlined fenders, but leaves aerodynamic drag between the wheels and the fenders, for example. Rolling friction is still there. For general purpose use, it needs springs and shock absorbers ... they consume energy.

I did not find much technical info. Diesel - battery - electric propulsion is known to be more efficient than Diesel - transmission - propulsion but only if you do not compute the cost of the batteries ... expect $4k to $6k for the Aptera every 5 or so years.

Just a guess ... the Aptera might exceed the Prius in seat mile fuel efficiency, but I doubt it will exceed the Boeing 747 or 787 on that figure of merit.

By the way, I found this while looking at the Aptera site:

http://www.popsci.com/cars/gallery/2008-01/hondas-truly-fluid-transmission

Seems Honda has TWO swash plate drives in its newest transmission!

Dude, cute about the aptera, but it's just another "bug". You have to realize that when they create these low weight, 2 seater bubbles that they cannot outdo the last centuries scooters.

I spent a couple months in Taiwan. 12 scooters to one '4 wheel vehicle'. They run on hummingbird like drops of gas compared to Europe, Austrailia, North American norms.

This so called ecobug carries as much, burns twice the fuel and is 20 times more expensive. The concept is called stupidity in motion. What is it supposed to replace?

I've seen 5 people on an 80cc scooter. The Aptera concept car couldn't hold it's own against a bicycle. It may look neat and have great gas mileage, but if it can't outperform a 50 cc scooter, it's doa. Stupid designers will kill a project faster than inadequate design.

If you can buy a 1500 dollar, 80 cc scooter that carries 2 people and gets 60 mpg, parks anywhere and is insurable for $50.00 a year, why would anyone buy something that gets 100 mpg, costs 30,000 dollars, takes up 8 times the area, still only carries two people and probably insures for $3000.00 per year due to it's replacement costs?

Looks neat and futuristic...solves nothing, carries nothing, replaces nothing....is nothing. Another attempt at someone designing something they think we should be told to use, not something we would use. Morons in design will produce moronic results.

Agree that the aptera is just another bug ... and we already have the 4 to 5 passenger Prius that gets 61 mpg in the new EPA rating scheme. That Prius is a tour de force of fine engineering. The sun and planet transmission is slick and functions as a continuously variable transmission, the fossil fuel engine only comes on when needed to recharge or add a bit of torque for acceleration. The alternator also functions as a motor and by driving the planet ring can either add (when in motor mode) or subtract (when in alternator mode) torque and speed to the output shaft. I saw one offer of $6800 for the replacement battery pack which our infinitely wise federal government has been subsidizing in new vehicles, but not for repair.

As a political observation, I love it, we are exporting jobs, and our government spends our tax dollars to subsidize a Japanese care and decides to purchase a French refueling aircraft! We are governed by a technologically illiterate, anumeric, self-proclaimed elite.

As is true with most "green" technologies, the Prius mileage figure does not include the energy cost of making and disposing of the batteries. It is a real cost. That is why the car did not sell until it got its subsidy.

Thermodynamics is a portion of science without, to my knowledge, unexplained empirical data. It tells us the limits of efficiency for all sorts of systems, pressure shift systems, temperature-shift systems, voltage-shift systems, spring based systems, etc. At available T and P, efficiencies are on the order of 60%, and we are approaching 30% in variable load designs like the Prius. The next 30% require a system that operates in thermodynamically reversible ways. No energy lost to friction, drag, cooling, vibration, noise etc. Also, nearly constant power operation ... no 6 second acceleration up the entrance ramp to the tollway.

That is where turbines, Starrotor, and other rotary engine concepts have an advantage over reciprocating engines, they operate closer to thermodynamic reversibility. There is no scientific secret that needs to found ... but it will require a very clever mind to make a more reversible and lower loss engine/transmission combination for automotive or peak energy generation affordable.

Got to run. Have a great day!

Tomkaighin wrote: "I'd like to know where you got the 15% number for air compression/recuperation. I'm not disputing it, I just don't really know that much about it. The issues you mentioned are becoming clearer to me, with the temperature exhausted compressing a gas and the heat required for re-expansion. I know the concepts, but not the working problematics."

The 15% number came from an engineering thermodynamics text book ... I do not have the specific reference handy. It was in a discussion that pointed out that in large manufacturing facilities the lease efficient energy system is compressed air. Three others are more efficient: rotating shafts, hydraulic systems and electric systems.

Perhaps I have left some participants behind by discussing adiabatic and isothermal. Let me suggest a simple inexpensive experiment that is not very precise but will illustrate the principles.

Plug the hose of a bicycle pump. Push the handle down as far as you can ... feel the bottom of the barrel to see that the air has heated up. Release the handle quickly and see that it rebounds to approximately its initial position. (Could make a neat pogo stick for grandkids this way)

Next, redo the experiment with a twist. While pushing down on the handle to pressurize the air in the bottom of the barrel, spray the barrel with a hose to cool it. After thermal equilibrium is reached, release the handle. Notice that it rises only part way towards its initial position. The lost heat energy can no longer do work. It took more work to compress the gas while heating it than you can recover after the gas has cooled in storage.

If after cooling the gas with the hose you pull the handle up to its original condition, the gas cools well below ambient temperature and you have done work to cool it by lifting the handle. This is an inefficient example of how an air cycle air conditioning unit would work.

If you have a truck with tire pressure of 45 to 60 psi, let a little air out in the morning when everything is at ambient temperature. Direct that air to a small thermometer and you will see that it is cold.

In summary:

work done to compress a gas increases both its temperature and its pressure.

work done by a gas causes its temperature and pressure to decrease

if heat is lost between compressing and expanding, available expansion work is smaller than available compression work. If lost heat is restored (as is done in utility scale compressed air energy storage systems) before expansion, the work of compression can be recovered.

In an extreme oversimplification that omits many practical issues. If you compress air enough, let it cool to ambient, and then let it expand, it will cool off enough to liquify. Then you can boil the liquid in a still to separate out commercial gases, among which are nitrogen, oxygen, carbon dioxide and argon. These have market value, but you can not drive the compressors at the front end of the plant with the evaporating liquid air from the back end UNLESS YOU REHEAT THE AIR.

I don't know if this helps, it is my first attempt to describe the realities with ordinary examples and with an experiment that most of us can do at home.

ps Someone mentioned GM heated intake air. In a carbureted engine intake air was heated to prevent icing in the carburetor ... this is still true of Continental and Lycoming General Aviation Engines in 2008. When reducing throttle for descent to land at 60 degF, I have experienced carb icing. With the throttle plate nearly closed and the engine pulling a vacuum on the back side, the pressure reduction lowers temperature to below 32 deg F, condensing atmospheric humidity which freezes on the wall and can lock the throttle plate closed. Not good if you need to go around to miss a deer on the runway! Once again, gas temperature drops when its pressure is quickly dropped.

Excellent, Smithers.

Ok, I may be a little flippant at times but I'm actually picking up tidbits of information that I didn't know in your heartfelt attempts to explain them to me. I may not pick them all up, but if I question or ignore pieces of it, do not take it as a slight on you, rather take if for what it is, my inability to absorb things that are not alcoholic.

hmmm, maybe if you had added C_nH_2n+1OH to you comment, my primed neurosystem would have accepted it more readily.

(hic)

Sorry to disappoint you but both the links you listed lead to non-starters. Both are deader than the starrotor company (which is teetering as we speak).

The internet addresses in message 28 are live as of 1243 hours CDT 30 Mar 2008. They are not live links, but if you copy them into the address box of your web browser, you will find live, interesting and informative discussions about compressed air energy storage in systems that are currently operating around the world.

Since you identify yourself as a painter of pressure vessels, I presume you know more about practical matters than I do. For the benefit of all participants, if air is the working fluid, it will need to be dehydrated while it is being compressed to minimize internal corrosion and to prevent icing when it is expanded while doing work.

Further, there are dangers of explosions if adiabatic expansion is used unless the air is carefully filtered and dehydrated as it enters the compressor for storage. More on this aspect as I find time.

HAVE FUN

In case you missed these earlier discussions

Esbucks comments seem to have some good points, especially the use of wet compressed air & using the heat generated in the best possible way!

http://cr4.globalspec.com/thread/17154/Prototype-for-an-Air-Compressed-Engine

http://cr4.globalspec.com/thread/10290/About-AIR-MOTOR

http://cr4.globalspec.com/thread/11677/Air-Car

You should search tom's post's & comments below, if you haven't already

http://cr4.globalspec.com/member?u=3190

I to am glad to see them continue with their experimentation, and forging on with this design. With the increasing costs of fuel and no apparent end in sight it seems as though we will need something like the starotor design.

I was curious though as to whether or not once completed if the engine design would allow the use of a refrigeration system for cooling of the block components to keep the heat down around the combustion chamber.

Also could this same design be used for burning fuels like hydrogen or possibly natural gas.

O well tell them to keep up the good work and best wishes to their efforts!

That's a valid point - when you have an engine block that is running (literally!) red-hot, the first thing I'd consider problematic is insulating the rest of the vehicle from it. Especially the fuel supply and passenger/cargo compartments. If I'm not totally mistaken, I seem to recall being told once that that was at least part of the reason for mounting military aircraft jet engines (and even some commercial aircraft) on standoff pylons.

The thermal control by refrigeration would be energetically expensive. Much of the shaft horsepower would be devoted to the coolant compressor. Expect a more conventional cooling system.

That said, the design team has completed the system engineering (but not production of equipment) for water injection. The water injection would lower the temperature of the gases entering the expansion section of the engine and increase their volume. Since work performed is the integral of pressure * volume change, this allows more work to be performed while keeping temperatures in the range tolerated by readily available engineering materials.

The starrotor, as an external combustion engine (external to the expansion chambers), is omnivorous with respect to fuel. Hydrogen, methane, propane, butane, ethanol, octane, diesel, aviation and any other non-particulate fuel can be burned. I doubt if powdered coal would be a good choice because of its effect on rotating seals.

With regard to cooling, as in an air conditioning system. A starrotor pump can pull a vacuum down to 4 or 5 inches of mercury. If water spray is injected into such a vacuum the water temperature drops to the mid 50s on a Fahrenheit temperature scale. The temperature falls due to evaporation. This is cooloant that can be pumped through conventional airconditioning heat exchangers for HVAC purposes. No more freon, ammonia or other refrigerants. Use a vacuum pump in an open system rather than a compressor in a closed system. The principle can be achieved with any vacuum pump having high volume, low delta P. There aren't many of those on the market.

y'ALL Have FUN

While I might understand your confusion, I don't think you quite get it...there may be heating and cooling issues because of expanding gases, there is no combustion on the starrotor design...nothing explodes, it is a pressure engine, hence the ecological terms and no mention of fuel other than air (though I suppose any compressed gas could be used for a 'fuel'. If you want to burn something, then there are several steam threads on this site you might want to look into.

I joined it as I am looking for a storage facility for self generated power. So far, best scenario I can come up with (for various reasons) is compressed air. Hence, I've been looking into compressed gas motors for transfering said stored energy back to a different form as needed by the consumer.

At the very least, re: my post #8 here - I am gratified to see that this is apparently significantly more than "um". This is in no way within my areas of expertise, so I am learning lots here! Mucho appreciated...

LOL, well then, since you admitted to bringing it up, I'm BLAMING YOU!

tomkaighin wrote: "I joined it as I am looking for a storage facility for self generated power. So far, best scenario I can come up with (for various reasons) is compressed air. Hence, I've been looking into compressed gas motors for transfering said stored energy back to a different form as needed by the consumer."

Torpedos have used swash plate drives for a long time.

Single or double acting pistons oscillating in axial direction, arrayed around the center of axial rotation. Swash plate position (angle between plate and axis) controls stroke and thereby controls the compression or expansion ratio. When plate is perpendicular to axis, there is no piston motion. When plate is at an angle, say 60% on the acute angle side, all pistons complete a full oscillation with each rotation of the shaft. Power can transfer either to or from the shaft as needed with variable compression/expansion ratio. There is a neat video on youtube:

http://www.youtube.com/watch?v=eRCUqcwqu5w&amp;feature=related

Just a thought for your compressed air storage scheme.

The starrotor in serial production would be an even better fit with fewer moving parts and lower friction and variable compression/expansion... but for now it is one-off production and expensive. On the other hand ... if your are a production engineer with production facilities available to you ... ???

In my minds eye, I see a compressor that operates when there is excess wind, solar or hydro power available and is used as an expander when there is a shortage of such power.

A Question, would you be heating the compressed air enroute to the expander in order to increase the energy recovery above pure adiabatic expansion?

Thanks for your input. To answer a few questions, I currently don't even have a space to test this out, as I am a travelling painter (high pressure vessels) so I travel the country in my trailer.

You are correct in your assumption that I am looking to have compressed air as the storage medium for other generation techniques when the load is less than the power produced and vice versa.

I hadn't arrived at the point in my idea to where the air would be heated or not, I would assume probably not, as that is another energy requirement and the expantion phase would be to produce energy when there was a demand (meaning the rest of the system is not producing enerygy. If there was some point in the system that was producing waste heat, that could be used to preheat, but I don't envision it yet.

Still early in development stage, and will probably take a back seat to a passive solar mintos engine as my first real build endeavor. It all revolves around becoming personally energy independent, at least in my home (third time is a charm, this time I just find a woman that already hates me and buy her a house, cut out the middlemen). Being able to run a vehicle on air power would be the next logical step, though that will take some time.

As to the slip plate, it was only used in very early torpedo designs (late 1880's). Most now are electric-battery driven, though compressed air flasks are still used in the launch tubes (permanent) an launch canisters (independent mounts). I'm not saying it won't work for my application, and I'm looking into it (better utube example is this http://www.youtube.com/watch?v=1T6KwJW6W7A&feature=related ). Nothing is out bounds, just whatever works.

If you want to talk to me further about it, feel free. You can contact me through here or straight by email if you want. Just drop me an email address and I will get back to you (though I would do it through a private message to me, dumping email addresses in a general post is an invitation for spam <evil grin>.

Again, thanks for your interest and observations.