rotary design as a steam alternative - engineAir

[Andrew Graham]

Perhaps this compressed air engine approach could be a great influence towards our design principles-

http://engineair.com.au/index.php?option=com_content&view=article&id=2&Itemid=2

I'm Andrew and this is my first post.  I'm hoping to proliferate the OSE philosphy and help construct the GVCS in Northern Australia.

It is designed for use with compressed air, but the pressure generated by steam could be very compaitble with this unique approach.  perhaps a design could be made to use either compressed air and steam in a modular fashion!  Now that is an exciting possibility for a power cube.  compressed air for storage of solar energy when possible, and steam from a an efficient burner when that option isn't available or longer run times are required.

Unlike a normal Wenkel rotary, the inner part of the compression chamber rolls around the outer, the parts being kept seperated by a thin layer of air, so there is practically no friction.  This eliminates the problem that rotary seals had.

They boast up to 96% efficiency. and it is extremely compact for its power it can provide.

To introduce myself, I'm transitioning from the visual effects film industry (currently and FX TD on Spiderman).  I'm good with Solid Works CAD, arduino, Python, film editing, aerial photography, drone based video, procedural modelling/phenomena.  I've printed my first PCB when I was 8 and finished final year electronics 2 years early in high school.  I've done some classes in blacksmithing and welding and am really keen to get into using a miller and lathe.  I'm currently in Vancouver, Canada, but hoping to develope OSE availablity in Byron Bay, NSW, Australia and Ravenshoe in Queensland.

[Mark Norton]

Nice to meet you, Andrew.

It turns out that there are some important differences between an engine that runs on compressed air vs. steam.  A steam engine relies on thermodynamics in a process called the Rankin Cycle.  Still, A Wenkel rotary engine does have interesting properties.  I had a car once that had a rotary engine (Mazda RX7).

Regarding OSE, I would urge you to contain OSE directly.  This form is largely focused on steam engine activities. 

- Mark Norton

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[Andrew Graham]

Thanks Mark!  The suggestion for the Engine Air compressed air motor design I was thinking would be appropriate to use as the turbine in the Rankin Cycle.  Since it seems to be a very efficient system that is using the flow of a compressed gas, the pressure generated from steam could work well here in place of the pressure source being compressed air.

[Russell Philips]

Hello Andrew,

I have wondered if there is a patent on the air engine?
Or have plans been made available?

I have been designing a cylinder that operates on pressure from phase change expansion followed by phase change contraction. The concept is sound and the main component is off the shelf.  The other components are not a difficult build.

In super heated steam applications, collapsing the steam in the cylinder reduces efficiency. In the phase change cylinder, it not only is a good thing, it effectively doubles outputs.

The most important aspect is that it only requires low temperature differentials to affect the changes in volume and pressure.

---

Date: Mon, 3 Feb 2014 14:46:22 -0800
From: que...@gmail.com
To: open-sou...@googlegroups.com
Subject: Re: rotary design as a steam alternative - engineAir

[Andrew Graham]

Yes its patented, I'd like to meet the inventor when I return to Melbourne one day though and see if he'd be interested in OSE.

That sounds like a good design Russel, is it similar to a sterling engine?

[Russell Philips]

Nope, Stirling engines and hot air engines do not phase change. These also work better the greater the thermal differential. This is new. The phase change cylinder is a novel approach harnessing both expansion and contraction forces.

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Date: Mon, 3 Feb 2014 16:29:09 -0800

[Max Kennedy]

Wasn't phase change the original premise of the watt steam engine? Inject steam, condense to create a vacuum?  Sounds like a development of that idea.

It can be done

[Russell Philips]

Thank you Max for finding this.
The watt steam engine and Newcomen both use expansion and contraction.
Are there any other developments of this idea through the following decades or more recent?

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Date: Mon, 3 Feb 2014 21:52:28 -0500

Subject: Re: rotary design as a steam alternative - engineAir

From: mekenn...@gmail.com
To: open-sou...@googlegroups.com

[Ken]

Lots of different topics here, guess I can address them one at a time, making it less difficult to reject them summarily.  :-)

I worked with HP air compressors in the Navy, Ingersoll-Rand N-20D 5000 psi HPACs,.  There is lots of heat generated in compressing air, I count 5 coolers, an after cooler, a frame cooler and oil cooler on each machine.  It is all low grade heat, so very difficult to recover and use for anything constructive.  HPACs were also very maintenance intensive, that it a lot of abuse for any machine to absorb.  When all is said and done, the compressed air is not a good portable power source.  You need really heavy and bulky flasks to transport it and the amount of energy per cubic foot isn't real impressive compared to something like gasoline.  If you do the calculations you realize that a compressed air cars range is in the tens of miles even with storage capacity way beyond that normally allocated for gasoline.

The rotary engine design is interesting, as most rotary engine designs are.  I have to note that there are literally thousands of rotary engine patents on file and none (including the Wankel) has been a commercial success of any note.  The first big issue is sealing, everyone pays a lot of attention to the rotor tips and very little to the rotor sides (which are huge), the Wankel is one of the few to really address this. Even the Wankel, however, is pretty leaky compared to the most modest piston engine; no one tries to do a 15 minute pressure leak down check with hopes of anything like the same result as a piston.  Another huge problem with rotary engines is that the volume to displacement ratio absolutely stinks.  The theoretically perfect container from a thermodynamic standpoint is a sphere, it contains the most working fluid with the smallest surface area from which heat can flow in or out of the vessel.  A piston isn't quite as good, but I don't know of a good way to make a rugged expansible sphere.  Then there is lubrication, Mazda spent fortunes developing some incredibly impressive seal technology...aluminum impregnated porous graphite structures, melting the tips with electron beams to harden them and get them smooth by having the metal flow and then cryogenically cooling them to freeze the grain structure.  The Mazda RX-8 still needed a small bit of oil injection to keep the wear under control.  

The engine in question raises questions.  How are they fabricating those semi-circular grooves in the housing?  How accurate can they hold the tolerances?  What kind of contact is there with the semi-circular blades on the rotor?  How are they sealing those channels?  Besides having large surfaces that can potentially rub and produce large amounts of friction, I really don't see much in the way of sealing in those channels if the engine is to be free enough to roll over easily.  If they are depending on very tight tolerances, it probably won't work under steam, the relative thermal expansion of the housing and different parts of the rotor are likely to cause it to seize up.

This engine also has a central, plug type, rotary valve.  Those things work great if you drench them in oil, the oil film minimizes friction and wear while making the valve moderately leak resistant.  If not lubricated, they either wear out rapidly or leak badly due to the needed gap...once again, thermal expansion dictates just how close you can fit the parts without getting binding at some point in the operation.

Another problem with central rotary valves such as this one is the long port(s) between the valve and the expansion chamber.  This long port increases clearance volume quite a bit, which in turn lowers thermal efficiency.  In a counterflow design, such as shown on the website, the two adjacent ports allows the cool exhaust to chill the incoming steam, transferring the energy from the steam to the exhaust without utilizing it in the cylinder.  There is also the problem of wire drawing.  Long passages cause flow turbulence and friction, which in turn causes the steam admission to occur over a longer part of the stroke; if the steam isn't admitted right at TDC it loses energy when it reaches the expansion chamber because the expansion is already under way and the pressure has already dropped...preventing the steam from expanding almost isentropically  and thus reducing efficiency further.

I'm bothered by the idea of doing phase changes inside the cylinder, or whatever.  Eliminating the phase change was the reason the Watt engine rapidly supplanted the Newcomen.  Causing the working fluid to condense in the piston allowed the condensate to chill the cylinder, which in turn robbed heat from the incoming steam.  The latent heat of fusion is very significant, so a large amount of energy can be lost for relatively little change in working fluid temperature.  Transferring the phase change to an external condenser eliminated these losses.  It has to be remembered that condensation (or contraction) generates no pressure with which to do work...there is no such force as suction which draws objects in...the low pressure zone allows ambient external push something into the low pressure.  A separate condenser allows an engine to do more work because now the steam doesn't have to exhaust against atmospheric pressure, but can instead exhaust into a partial vacuum.  This low pressure exhaust makes it feasible to employ shorter cutoff and expand the steam further, wringing more energy from it (assuming the pressure and temperature were high enough to permit using the longer expansion efficiently, over expansion reduces output),  Keep in mind that longer expansion means lower Mean Effective Pressure to overcome friction and associated cycle demands such as feed pumps and blowers.  In any case, to the best of my knowledge, no one has revoked the Carnot Cycle.  The limits of any heat engine efficiency is proportional to the difference between the absolute admission and the absolute exhaust temperatures.  Subatmospheric exhaust into a condenser allows the steam to expand further and reach lower temperatures, increasing the difference with the incoming temperature and improving output. Simply changing phase inside the working chamber doesn't lower temperature a bit, so in and of itself should not have a significant impact on overall theoretical efficiency.  In fact, the phase change WILL lower pressure, which is beneficial....but the pressure drop makes it harder to condense the steam and produce a phase change.  You are back to Newcomen extracting heat from the working vessel to the detriment of the incoming steam energy.

Sorry to sound so negative, but these are almost all innovations that have been popping up with fanfare for the last 150 years, and then dying away again. Traditional steam engine design wasn't 'laid out" by anyone as a series of arbitrary rules and then adhered to, countless developers tried a myriad of different approaches and over time the designs coalesced around those features that consistently produced the best results. 

I've been working on a very basic tutorial on steam power for SACA, feel free to glance at it and see what you think:

 http://nrcreunion.magix.net/public/saca/index_2.htm

Regards,

Ken

[Russell Philips]

Holy cow!
Wow, those pages look fantastic!
There is massive information and well delivered.

 I have a question about the 'D' valve slide.  How does it seal? Any leakage directly shorts to exhaust. It appears to hold back tremendous pressure in a very short distance, while still allowing movement. It is not clear from the illustration.

Is this a machined cylinder inside a machined tube/housing of types?
I like the 'D' valve DA cylinder very much. I believe this is the direction I would pursue for a homestead steam engine. In many cases my steam engine development motivation is thwarted by existing solar PV panels (which continue to get cheaper).

Another question - What keeps a crosshead attached to the piston in a DA application?

Ken, your postings are always complete. You cover your points with information to back.

We are not all of the same understanding and words do not always convey a thought, filters and interpretations do not help.

It may take some time to discuss phase change discoveries and theory. I am often wrong but am quick to see another possibility as I am made aware. I seek greater understanding and truth in my research and development. Failing is only steps to completion. I'm not done yet!

I am looking for a discussion to help uncover any misgivings or to improve the design. It appears sound. I am ready to present this into the public domain. I'll start a new thread.

---

Date: Tue, 4 Feb 2014 05:08:54 -0800
From: ken...@aol.com

To: open-sou...@googlegroups.com
Subject: Re: rotary design as a steam alternative - engineAir

[Russell Philips]

Okay, I missed the obvious with the 'D' valve. Like a cup covering the exit holes, the greater the pressure the greater the seal. This is probably flat and wears to self seal - very cool!

---

From: russell...@hotmail.com
To: open-sou...@googlegroups.com
Subject: RE: rotary design as a steam alternative - engineAir
Date: Tue, 4 Feb 2014 09:29:52 -0700

[Russell Philips]

I am seeing something that may reduce the manufacturing or build difficulty of the DA cylinder. Would separating the valve body from the cylinder sidewall allow the use of an off the shelf DA pneumatic cylinder? Yes, attaching flexible high pressure lines would increase the unswept volume adding to inefficiency, but the decreased complexity may justify it. It also allows new design orientation potentials. I like opposed cylinders because the throw out weight is balanced.

---

From: russell...@hotmail.com
To: open-sou...@googlegroups.com
Subject: RE: rotary design as a steam alternative - engineAir

Date: Tue, 4 Feb 2014 09:42:10 -0700

[Ken]

Hi Russell,

Glad you like the website in progress :-).

"D" valves seal reasonably well.  The pressure on top of the valve is full throttle pressure while underneath is the exhaust port, so the pressure differential forces the moving "D" element down onto the valve face.  It goes without saying, these things also need a lot of lubricant else they tend to wear out rapidly.  D valves are not suitable for highly superheated steam or great pressures, high temperature and the requirement for lots of lubricant are not a good mix.  High pressure can push the moving and stationary assemblies together too hard, producing excess resistance.  For high temperature and pressure a piston valve is used, it is similar to a D valve but round, the pressure is balanced in all directions and sealing is accomplished via piston rings.  As I said, D-valves seal reasonably well.  A designer some years ago noted that there were exactly two types of engine valves, poppets and those that leak; I've found no reason to argue with that observation. 

D or piston valves would be my choice for an authentic, period steam launch or other hobbyist replica; you simply can't beat the romantic feeling they impart.  For a practical modern engine where efficiency and power are a concern, I would go with poppet valves for a number of reasons:

Pressure forces the valve shut, giving a tight seal.

There is minimal side load which nullifies lubrication issues (car engines have seals to keep oil out of the valve stems).

The poppet can open directly into the cylinder, eliminating the clearance volume associated with the steam passages, improving efficiency

Poppets don't pass incoming and exhaust steam through the same passage, the cool exhaust doesn't chill off the incoming hot steam to anything like the same degree.  Almost not at all with uniflow exhaust.

I'm not sure I'd be thrilled with a pneumatic cylinder, most are not rated for great pressure and the ability of the seals to handle the temperature might be questionable.  Not that it isn't possible, Sylvester Roper's steam carriages from circa the Civil War used flexible rubber hose to carry steam to the cylinder---but we have no idea how well this held up.  Maybe a better alternative would be to purchase off-the-shelf hydraulic tube; this stuff is readily available to build hydraulic cylinders and comes bored to size and honed.  One supplier is:  http://www.nationaltubesupply.com/inventory.php

Opposed cylinders don't gain you a lot with a steam engine.  Gasoline engines, being 4 stroke, can have opposed layouts and fire each cylinder on every other revolution to even out the power pulses.  Steamers produce a power stroke every revolution, an opposed design would cause both cylinders to deliver power simultaneously, from a smoothness point of view this is identical to having a single cylinder.  I specialize in engine balance and will admit the opposed layout is better balanced, but unbalance forces go up as the square of RPM, so the issue is less severe at lower speeds.  A single balance shaft could cancel out a large portion of the unbalance from a single piston.

Double acting engines are often two cylinders laid out with the crankpins at 90 degree angles (or a 90 degree V sharing a single crankpin).  In long cutoff this means that one end of one cylinder will always be at or just after TDC and the engine is self starting and readily reversing with the correct valve gear.  I won't bore you with the math, but an inline 2 cylinder with 90 degree pins is a pretty horrendous solution from a balance point of view but all those Stanley steamers and steam launches had no problems with it because the DA engine is also not suited for high rpm due to the much greater reciprocating mass imposed by the crosshead. 

DA and SA engines both have their points.  DA get two power pulses per stroke per cylinder.  The crosshead, piston rod and seal prevent steam from leaking into the crankcase and contaminating the lubricant.  SA engines rev more freely and are simpler to build per cylinder as you don't have the same needs to keep the bottom seal, cylinder bore and crosshead all very accurately aligned.

Most DA engines were castings with sand cores being used to cast the steam ports into the block.  There have been a few with cylinder sleeves and gaps between the casting and the sleeve serving as porting.  Whatever works and is readily achievable.

There is no single answer to fixing the piston rod to the crosshead.  For those rods that are screwed into the crosshead I've seen them lock wired in place, held by a retaining pin bored through the crosshead perpendicularly to the piston rod and in one instance the top of the rod had a hexagonal boss on the top and the rod had a hexagonal flange just above the threads...a special washer with six wings on it was bent to engage both hex surfaces simultaneously to prevent the parts from walking away.  I've also seen piston rods with no threads and a flange on the base.  A cap fits over the piston rod (before you install the piston) and drops down onto the cross head, capturing the flange in place between the cap and crosshead.  In this style the hole in the cap is usually a bit over sized, allowing the piston rod to self seek a bit in relation to the cylinder.

Hope this helped a bit.

Regards,

Ken

[Andrew Graham]

Thankyou ken, thats an amazing breakdown.  you dont sound negative, your input is great!

This is a thought experiment I suppose.  I like the idea of the versatility of the engine if it can be achieved.  he does say that he can use it with almost any fuel in an interview, but he doesn't want to, based on his own environmental beliefs and motivations it appears.

It would be great to have an engine that could use compressed air for low range, high torque work but be able to use other combustible fuel sources for extended ranges/durations or if compressed gas were unavailable.  I just figure if the premise of the engine is to function from any expanding gas from pressure, then why not steam too?

--------------------

In the engineair design those channels are sealed with a set distance in mind (maybe we shouldn't say its sealed?), they rely on dynamic air flow to reduce friction.  See 1:40 that he can slide a piece of paper between those semicircular blades and the outer chamber.  I can't speak for the accuracy of their manufacturing process.

http://www.youtube.com/watch?v=1qOsHteptM4

There is a layer of air between those components achieved at 1PSI to reduce friction.  They sacrifice a small amount of pressure to improve the longevity of the motor it appears.

http://www.youtube.com/watch?v=ZGiviT-C_oY

Jump in 1:30 to see how low the friction is on the rotor as it rotates around the outer housing.  This is pretty nifty too.

If condensation could cause it to seize up, what about maintaining some heat in the chamber to help prevent condensation with a heat exchanger?  the condenser could still sit further down the line and be used to produce a vacuum on the output of the engine.  Could it be designed a calculated variation of the "gap" in mind to be more appropriate for steam?

-----------------

On another note-

Does atmospheric pressure affect the energy required to perform hydrolysis?  probably.  still, I was wondering if you had a closed reservoir (gas cylinder) of water, if you seperated the air and hydrogen in a contained tank with hydrolosis, and then end up with compressed hydrogen and oxygen in the same volume.  that could be damn useful to have a combustible source under pressure.  even if a little more inneficient, it could be a cheap alternative to a compressor.  and could be a good long term storage mechanism for excess solar energy in peak collection periods if battery banks were filled.  you get pressurised clean combustible fuel to use produced by the sun.  in small storage cylinders this could potentially be safe enough for low range agriculture work, and for welding or using a forge.

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[Andrew Graham]

replace the word hydrolysis with electrolysis - sorry about that typo

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[Ken]

Hi Andrew,

I'll admit, the developers presentation turns me off right from the get-go.  They are heavy on the advantages of air power, but I know of no engineer in the auto industry that takes the concept seriously; it isn't even difficult to see why, they are using electric power to turn a motor to run a compressor to put air into a flask to turn an expander to move the vehicle.  There are a number of energy conversions in there, each of which induces significant losses, you could just charge a battery and run an electric motor. skipping all the intermediary steps, and get the same final result at much higher efficiency. That's not even counting the costs of procuring and maintaining the compressor.  This isn't the only company touting air motor vehicles and none of them actually show a detailed analysis of how this is supposed to pay off in the real world.  These people usually manage to get by with some sort of campaign designed around the idea that it "Runs On Air!", talk about the wonderful benefits and get vague on all the gritty details.

I'm also more than a bit skeptical about their efficiency claims.  You are only going to get efficiency that high by expanding the gas down to about atmospheric and extracting energy every bit of the way....then exhaust that gas without using any noticeable energy.  That sounds good, but have you ever seen any engine that has almost no exhaust pressure?  Expanders reach practical limits.  You can't really expand all the way down, you need to leave enough pressure in the cylinder to cause the gas to flow out on the exhaust stroke.  If you don't do that, the engine will have to push the gas out and invoke a pumping loss.  Heck, you probably get a pumping loss in any case; as the gas exhausts the pressure drops and there is less motivation to leave the cylinder, so at least part of it is going to have to either be compressed or pumped out. So the goal isn't to eliminate the pumping loss so much as to find the sweet spot that minimizes it.  In any case, pumping losses are going to limit peak efficiency.  You are NOT going to see 96% in any real working engine.

As far as the seals go, I have some first hand experience with the basic concept.  Naval steam turbines with which I have worked use labyrinth seals to reduce leakage between the shaft and the housing.  The labyrinth packing uses a series of grooves and close running fits, the grooves improve the performance dramatically as they rapidly induce turbulence that partially blocks flow.  Use of progressive grooves creates far more turbulence than a simple close running fit, improving utility. Labyrinth sealing effectiveness varies based on mean pressure differential and residence time.  A large pressure differential will cause much more leakage than a small one, in an engine the pressure is constantly varying throughout the stroke so the MEP, mean effective pressure, is a better indicator.  Two engines can have the same admission pressure, but the one having more expansion has a lower MEP and less total loss.  Residence time in an engine is going to be a function of RPM.  At one rev there is plenty of time for the gas to leak by, at 10,000 hardly any at all.  So it's becoming obvious that these seals are not going to be as suitable for engines lugging under a load.

As I noted before, almost every rotary engine design I have seen goes to great lengths to seal the rotor tips.  I suppose this is because you mostly look at the side view when drawing it up.  This says nothing about preventing leakage down around the sides of rotor in the direction of the shaft.  I have trouble buying the turbulence explanation simply because Mazda builds Wankels to high levels of accuracy and they have found the need to have actual seals on the sides of the rotor...the similarities are way too great for the problem not to apply equally to both engines.  The same problem occurs in their rotary valve.  You can push the valve and seat together, but that wears like mad and produces enormous friction.  If you leave a gap it has some issues because the residence time is now 100%.  How do you prevent air or steam from skipping straight from the admission to the exhaust without entering the engine proper?  

Actually, when you get right down to it, way back when they built very long pistons in gasoline automobiles, it wasn't really until the 50s that the light slipper piston started to make inroads.  Those long pistons should provide a sealing effect as good as what these people are claiming, but I note that they were using piston rings from the very beginning as steam engine builders had likewise found them necessary.

Actually, the leakage brings up a good point.  Given that there is a certain amount of leakage and that it isn't utterly negligible, how do they get the high level of efficiency they claim?  Even 5% leakage is going to dramatically affect the bottom line enough to invalidate their 96% claim.  

It wasn't condensation that I was worried about when it comes to seizing the engine, but thermal expansion.  Air and steam have some notable differences.  A really efficient steam engine wants to use steam at 800 F, or preferably higher.  If we admit that steam to the engine, it is going to heat up the components.  As the steam expands in the engine, the steam temperature drops.  Different parts of the engine receive different exposures to steam at various pressures and these parts have varying geometries that affect their ability to absorb or radiate heat; they will experience different temperatures one to the other. If the housing or rotor sees a temperature much different than the other, it will expand differently; given that close tolerances are needed and that parts are sliding against one another, there is a strong possibility that you will see conditions where the relative expansion of one part relative to another will cause them to mechanically lock up.  The fact that they use curved vanes inside of curved grooves causes me some concern.  Same goes for the rotary valve, it is a plug type and differential expansion can either bind the valve or cause the gap to enlarge, increasing leakage.

I also wonder about tribology (lubrication).  Those long, curved wings on the rotor are going to rub up against the side walls of the housing.  Any demonstration of the engine running at very low PSI is avoiding mention of the fact that there is a pressure differential across those surfaces and the force applied against the housing will rise with operating pressure.  Put high pressure air or steam in and run it at high rpm and the friction will be pretty great, that alone will trash any 96% efficiency claim and probably reduce life expectancy to an unacceptable number of run hours.  You can lubricate those surfaces, but now you have to contend with injecting oil.  Given the size of the surfaces, it is going to take a lot more oil than the Wankel with its minimal tip contact.

I'll plead guilty to being highly cynical regarding new basic engine geometries, they have been popping up like clockwork seemingly forever and none make any headway.  The basic piston, rod and crank geometry is still dominant because it works, works well and produces the fewest number of trade offs.  I've found that most alternative designs which brag about a lower part count usually employ components that would be so problematic to fabricate and perfect that the benefit doesn't match the investment.  Take this engine as a case in point.  That rotor, with the wings, is no easy thing to fabricate.  Then you need to somehow cut matching passages in the housing...and do all this to high precision.  It's much easier and cheaper to simply cast an engine block with 6 cylinders, bore and hone the cylinders in a gang operation and stick in pistons which are mostly just turned and rods which are bored and sized on each end.  Maybe there are more operations, but they are all very simple operations that can be preformed cheaply, rapidly and accurately.

Hope this provides some basis for discussion.

Regards,

Ken

[Mark Norton]

>   I have a question about the 'D' valve slide.  How does it seal?

Like many valves, the seal depends on clean machining of the interface and the pressures exerted on it. Tightening down the slide value will reduce leakage, but increases operating friction.  It's a trade-off that can be tuned to some extent.  Lubricants such as graphite help.

- Mark

[Andrew Graham]

I suppose without seeing the air engine function and see the inventor answer questions like what you've posed I'm not sure where it could go next.  Sounds like we should get you to interview him!

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