COPYRIGHT (C) 2007 By Vernon Nemitz
Intellectual Property is described here. Modern Copyright laws give great power to the Copyright holder, regarding the making of copies of Copyrighted Intellectual Property into ANY medium. In this particular case, the author is allowing copies to be freely made into MOST media, provided the entirety of this Copyright notice/explanation is retained. However, if copies are made in the realization medium, the medium of constructed artifacts, the author MAY require a royalty payment to be made, of $10 per copy. In more detail, a copy of this engine that you make in that medium mostly by yourself and for yourself can be done for free. If you hire a "third party" to make of a copy in that medium, or if you make a copy in that medium and sell it, then the $10 royalty should be paid for that copy. (This is a small amount compared to the cost of making a copy of the engine in that medium, and the author hopes you will eventually deal with millions of them! Also, note that as time passes, while making/selling millions of copies, inflation can be expected to trivialize that royalty, by the time the Copyright expires.)

As additional logical support for some of the above statements, consider that a copyrightable document is generally supposed to be literary or artistic in nature (or even be a computer program). It is a modern thing to consider a work of engineering to be art (famous example: the Golden Gate Bridge in San Francisco), but documents describing aspects of the art of engineering (or describing any other art, for that matter, or even one particular work of engineering art) have been validly copyrightable for many decades. The present case is a document that describes (partly with diagrams and other variations of "artwork") the basics of how to build a gadget, which has a chance of qualifying as being "elegant", especially if it solves a problem well, that previously had not been solved well. (Even if it isn't "elegant", and is called "bad art", that piece of engineering is still qualifying as "art", heh.)

Next, suppose it is built, and the gadget without any documentation is handed over to somebody knowledgable in that field. Could we reasonably expect that person to be able to "reverse-engineer" the gadget? Doesn't reverse-engineering involve creating documentation describing how to build it? Even if there are few similarities of phrasing between the original and reverse-engineered documents, remember that that is equivalent to what can happen when text is translated to another language and back again. Copyright covers translation from the original language--the author's permission can be required. So it logically follows that copyright should be able to cover the translating of the artistry of a gadget-describing document into the realization medium, especially because that translation is reversable. In this particular case, the author's permission can generally be obtained for the low royalty/price of $10 per translated copy, in that medium, and is freely granted with respect to most other media. (If you have questions, ask! My email address is neither secret nor difficult for a search to find.)

Copyright law provides for significant penalties if a Copyright is violated, and the penalty can accumulate based on the number of violations. The author recommends that the Copyright on this particular Intellectual Property not be violated.

So, folks, the first half-baked notion here starts with a problem that modern Copyright laws have: They try to broadly cover copies made in so many different media, with more being developed all the time, that to avoid obsolescence and constant editing it is simpler for the laws to specify "any medium" than to specify a list. The suggested consequence is the idea that a Copyright may then be a better thing to have, than a Patent. Copyrights are easier and less expensive to obtain; the penalties for blatantly violating a Copyright can be about as stiff as the penalties for violating a patent, and the duration is much much longer! (In the USA that's 17 years for a Patent compared to something like 70 years after the death of the author, for a Copyright.)

Note that even if I am mistaken here about the breadth of modern Copyright law, even U.S. Patent law grants me a year after publishing an idea, to Patent it. Certainly nobody else can write a Patent application for this, partly because I'm declaring here-and-now that to do so, since it would be a translation of this document into the language of legalese, will also be a violation of this Copyright!

[NOTE added Nov 3, 2007: One of the links is "This Idea as a more ordinary Web page". A number of images having separate links on this page are embedded into that page, so you might prefer viewing the Idea in that format.]

The second notion here concerns the SPARLVE and RSE (variations on a theme, they are). Like most coined words, especially an acronym like SPARLVE, it looks ugly until you get used to it--but let me assure you it's even uglier if you can't pronounce it! (Thinking up an accurate description that made a pronounceable acronym took significant effort; the acronym is detailed in the subtitle of this Idea.) Anyway, for years I've been wanting to dream up a purely Rotary version of the Stirling Engine, one of the most energy-efficient engines ever invented. See the "Stirling Description" link. Please take some time to study that link, especially the engine diagrams, because I'm about to mention a number of things from that link, in order to show why a SPARLVE (mostly) qualifies as a Stirling (and an RSE can be exactly that).

To begin: A standard Stirling engine normally exhibits reciprocating motion of usually-two pistons, and if this can be replaced with rotary motion it would be even more energy-efficient. That is, reciprocating mechanical systems generally waste energy to make motion in one direction stop, and to start motion again in the other direction, so preventing that wastage automatically means efficiency goes up.

The two pistons of a standard Stirling engine are connected 90 degrees "out of phase" with each other. Please note that the word "phase" has a particular meaning here which is different from another meaning that was used in the subtitle, and will be explained later on. Here it refers to part of the 360 degrees of a full/normal rotation-cycle. Remember that a piston is usually connected to a "crankshaft", so that its reciprocating motion can be converted into rotary motion. One point in the cycle of a piston's motion is usually called "top dead center". At that point, a piston starting its motion for the first time MIGHT cause either clockwise or counterclockwise rotation of the crankshaft--most Stirling designs aren't picky about which way they rotate, and it can be troublesome to make one always rotate the same way when starting up. (Putting a flywheel on the crankshaft ensures it keeps rotating in the same direction, once started.) Heh, it can be troublesome even to get a Stirling started--many designs are not self-starting. Well, if one piston starts out at top dead center, and then it moves so that the crankshaft rotates 90 degrees, and now the second piston is at top dead center, this means that the second piston is 90 degrees out of phase with the first.

A SPARLVE and an RSE both feature at least two rotors, and in either engine the rotor shapes are distinctive enough that it can be easily seen that one is oriented 90 degrees out of phase with the other. (There is a variant design described later in which they are 60 degrees out of phase with each other; would that still qualify as a Stirling? Possibly so, because some variants of the Stirling engine have more than two pistons, and when the total is divisible by three, a 60-degree phase angle is not unlikely.)

In an original/standard Stirling engine, one piston is the power piston and one piston is called "the displacer". They are often different sizes to meet their specific purposes. Also, the power piston is "double-acting" --it is powered in both of the directions in which it moves. This is the main reason why the engine can work even though the two pistons are 90 degrees out of phase, instead of (like in other engine types that have two cylinders) 180 degrees out of phase. The power piston is pushed while the crankshaft rotates 180 degrees, and "pulled" (explained below) for the other 180 degrees of a complete crankshaft rotation, and the displacer is simply carried along for the ride.

The minimum two rotors in a SPARLVE --or the minimum two rotors in an RSE-- can be identical. This is workable because both rotors can act like power pistons and both can act like displacers, AND both can be double-acting. One consequence is that most variants of these engines should almost always be self-starting, and also almost always have a preferred direction of rotation.

A standard Stirling engine uses a gas (like air or hydrogen or helium) as its working fluid. The engine features a place which is always heated, and another place which is always cooled. (One of the major inefficiencies of early steam engines was that various parts of the machinery were alternately heated and cooled; in a Stirling this happens only to the working fluid; each piece of hardware stays at mostly the same temperature, which significantly helps its overall energy-efficiency). When the gas expands its volume in the hot zone, it pushes on the power piston, and when its volume contracts in the cool zone, it "pulls" on the power piston. I put that word in quotes because more accurately, a partial vacuum is created by the contracting gas, and gas in other parts of the system will act to fill that vacuum by pushing the power piston toward it. So, while it may be convenient to think that the piston gets pulled (and I will continue to use that word in quotes), it actually gets pushed in both of the directions it moves.

A SPARLVE or RSE also has an always-hot zone and an always-cool zone. An RSE, a true Rotary Stirling Engine, would use a gas as its working fluid, while a SPARLVE would use a substance that undergoes liquid-to-gas or gas-to-liquid "phase changes" (to invoke the other meaning used here, of the word "phase", regarding a state/type of existence). A possible problem is that the edge/surfaces of the rotors are alternately exposed to both the hot and the cold zones, and so at least the exposed parts of the rotors should be made of, or coated with, a thermally insulating material, to minimize temperature changes of the rotors (and to minimize energy wastage).

Each rotor of either a SPARLVE or an RSE is basically a simple disk of arbitrary thickness, with an axle through its geometric center and four particular features at the edge of the disk. Two of those features might be called "lobes", and the other two might be called "notches". Going around one rotor-disk, and starting at a lobe, then at 90-degree intervals you will encounter a notch, then another lobe, then another notch, and then you are back at the first lobe. The minimum two rotors are mounted in contact with each other so that either they are round-edge-to-round-edge, or one has a lobe fitting into a notch of the other, much like meshing gear teeth. For the moment, let's assume there are two actual gears behind-the-scenes, having 1:1 ratio, ensuring that the two rotors maintain their relative orientations accurately (the gears are not essential, as will be described later). In both a SPARLVE and an RSE, the notches must be larger than the lobes, and an RSE generally must have considerably larger notches than a SPARLVE (that's really the only required difference between the two, besides the choice of working fluid). I should state here that a variant design mentioned earlier could have six instead of four "particular features" per rotor--that's three lobes and three notches, of course (and leads to one rotor being 60 degrees out of phase with the other). Obviously it is physically possible for the rotors to have even more lobes and notches, but the "law of diminishing returns" happens to apply to implementing that. More about that below.

Now let's focus on a SPARLVE. I've created an animated .GIF to accompany this description (see link). DO NOT ASSUME THAT THE DIMENSIONS OR DIMENSION-RATIOS IN ANY OF THE IMAGES ASSOCIATED WITH THIS DOCUMENT ARE THE ONLY THINGS COVERED BY THE COPYRIGHT. Many obvious variations on the theme are quite possible, besides the things just mentioned in the previous paragraph, such as smaller rotors with relatively larger lobes, or larger rotors with relatively smaller lobes. The composition of the rotors is not specified, but it is obvious that they need to be made of something that can survive while doing the work expected of them. The axles in the animation are portrayed as points; it is obvious they need to be rather more substantial than that. Even the shapes of the lobes and notches might be varied. And while the word "HEAT" indicates the hot zone, it should be obvious from the portrayed effects of gravity (in the animation), upon the liquid in this particular portrayed orientation of a SPARLVE, that the place marked "HEAT" isn't the only spot that should be heated. (So why should the place marked "COOL" be the only spot that should be cooled, eh?) The word "zone" has been used here specifically to allow its extent to be arbitrary/whatever-works. And all of THAT is part of why this Intellectual Property is broad, not narrow. Got it?

You may wish to copy the .GIF animation and open it with a well-featured image viewer, especially one which can let you enlarge the image. You can easily see the 90-degree phase angle in the relative orientation of the two rotors, and the hot zone, cool zone, and "displacement zone" are clearly marked. You can see how gas that expands in the hot zone can push on lobes of both rotors, and how gas that contracts in the cool zone can "pull" on lobes of both rotors (making both of them double-acting, as previously mentioned, for both a SPARLVE and an RSE). The key fact behind a SPARLVE is that when a substance "changes phase" from a gas to a liquid or vice-versa, there is typically a 1000:1 change in the volume of that substance (some can do better; the steam-to-water ratio is actually 1600:1). The high relative density of a liquid provides an easy way to transfer significant amounts of substance from the cool zone of a SPARLVE into the hot zone, without reciprocating motion (or special plumbing with one-way valves) being involved.

In order to maximize the percentage of fluid that changes phase in a SPARLVE, it is necessary to NOT over-heat the fluid. There is a technical thing known as "the heat of vaporization" which must be added to convert a liquid, at the boiling point, into a gas. The gas will automatically exert pressure on its surroundings, and in a SPARLVE it powers the rotors. If there is strong resistance to its expansion, then the temperature may need to be raised some to increase the gas pressure. But we don't want to over-do this, because in the cool zone of a SPARLVE, we want a significant part of that gas to condense back into the liquid state. The hotter it is above the condensation point, the more difficult that will be, to do, because we have to first cool the gas down to the condensation point and THEN also remove the "heat of condensation" (identical in magnitude to the heat of vaporization) for it to become liquid. And this has to be done rather quickly, if you want to see a fast-rotating SPARLVE.

Fortunately, we likely need only a few milliliters (cubic centimeters) of liquid in a SPARLVE (the needed quantity is directly related to the third measurement-dimension, the thickness of the engine, not shown in the animated .GIF). Most of the "working volume" of the engine, the space in which boiling/displacing/condensing happens, will be occupied by gas. Such a small amount of liquid means it can fairly easily be raised to its boiling point, allowing faster start-up of the engine, and faster boiling/condensing for faster rotor motion. This might be improved by selecting a low-boiling-point liquid that also has (compared to water) a modest heat of vaporization/condensation (ethyl alcohol, for example). Thus the total magnitude of heat energy that must be added to boil the liquid in the hot zone, and removed to condense the liquid in the cool zone, can be very reasonable. A true Stirling engine is a pure "Carnot Cycle" engine, which requires large temperature differences between the hot and cool zones to maximize power production efficiency. See the "RSE-60" link, to see the Rotary Stirling Engine design that has three lobes and notches (six "particular features) per rotor.

Six MAY be better than four, but eight is very likely not better than six. Odd numbers are not possible unless one rotor has lobes only, and one rotor has notches only, in which case such an engine may be a "more accurate translation" of the original Stirling design from reciprocating to rotary motion, with only one power rotor--a dubious "advantage", that. See the "RSE-1" link for some diagrams that show the odd number of ONE feature per rotor.

But a SPARLVE is a heat engine that does NOT pay much attention to the Carnot Cycle to get its work done. See the link to the "Ice Engine", an Idea that was posted specifically to prepare the mental landscape for the SPARLVE. Both are phase-change engines, not Carnot Cycle engines.

One thing that a Stirling engine usually has, not previously mentioned here, is an add-on gadget known as a "regenerator". It's purpose is to pre-cool the gas moving to the cool zone, absorbing heat energy in the process, and to use that energy to pre-heat the gas moving to the hot zone (becoming itself cooler in the process). A regenerator makes a major contribution to the overall energy efficiency of a Stirling engine, and therefore this design (both SPARLVE and RSE) needs to have it, or an equivalent to it. How? In preparation for that, see the "Casing" link.

To help ensure that the hot zone and the cool zone are thermally isolated, when the casing of the engine is often likely to be made of metal, it is suggested that the casing be divided into three parts: a "cool zone assembly", an "axle zone assembly" and a "hot zone assembly". I'm calling them "assemblies" here simply because that might be an easier way to make them, than, say, to cast them into the correct shapes, or to machine them out of large blocks of material. I do not rule out the notion that somebody might decide to ignore the thermal isolation issue and construct the casing in a different way altogether, hoping to get around the Copyright. Sorry, every casing is going to need certain things in common (ways for thermal and mechanical energy to get into and/or out of the engine), and THAT's covered, regardless of details of construction. Of the two most obvious outer dimensions of the engine, the two diameters of the side-by-side rotors tends to approximately specify the longest measurement (call it "length"), while the diameter of one rotor approximately specifies the next dimension (let's call it "height" here). If we divide the height into roughly thirds, then each of the casing assemblies has approximate dimensions of the whole length and that one-third height. When combined into a complete casing, thermally insulating gaskets can be used, in fulfillment of the goal of this paragraph.

The hot-zone and cool-zone assemblies need a way for thermal energy to be transported from the exterior of the casing to the working volume of the engine. The assemblies could be solid chunks of material honeycombed with passageways for appropriate fluids, such as radiator coolant for the cool zone assembly and hot gases for the hot zone assembly. Or the casings might constitute a thin shell of material surrounding the working volume of the engine, with lots of heat-conducting fins. No matter what variation of these notions is tried, for a SPARLVE we now need to remember that we need not have a huge temperature gradient, which makes adding a regenerator fairly easy. For an RSE the task is less obviously managed, but not impossible (especially if yet another variation of the design is used; more on that below).

Now see the "Regenerator-1" link, for a SPARLVE. It portrays a system in which a heat-carrying fluid is passed through the cool zone of the engine, then through a heater, then through the hot zone of the engine, then through a radiator, and then back through the cool zone. For energy-efficiency purposes, this fluid needs to have as much as possible of a special property known as "heat capacity" or "specific heat", which is the quantity of heat that must be added or removed to change its temperature by one degree. To see why we want to maximize that property, let's imagine some Quantity X of this fluid NOT passing through the cool zone assembly of the engine, but just sitting there occupying space. As the vapor inside the working region reaches the cool zone, some of its heat can be passed to the exterior fluid. It should be obvious that the higher the heat capacity of that fluid, the more heat it can absorb before we MUST replace that warmed fluid with a new batch of cool fluid, if the overall goal of the engine's cool zone is to be met. In essence, then, the higher the heat capacity of this exterior fluid, the more slowly we can pump it through the the other parts already described--and the more slowly it moves, the less energy is spent in moving it, and in overcoming friction-equivalent things like turbulence. From such simplicities do increased energy-efficiencies result.

The way that exterior fluid acts like a regenerator is somewhat subtle; it is an "indirect" regenerator that is being described here. Basically, when the fluid passes through the cool zone and picks up heat, this means that the fluid does not need to be heated so much, before it passes through the hot zone and gives off heat. Likewise, after giving off heat in the hot zone, it need not be cooled so much in the radiator, before once again passing through the cool zone. So we have replaced direct effect of a typical Stirling regenerator with the indirect effect of doing thermal regeneration in an intermediary fluid, between the actual heating and cooling parts of the engine. The main reason this was chosen has to do with the very small region in the center of the engine, where condensed liquid passes from the cool zone to the hot zone. It's just too small a region, and liquid passes through it too quickly, for any significant direct-regeneration effect to be possible there.

There is one drawback to the preceding. When first heating up the engine, rather more than a few milliliters of fluids must be warmed, since the intermediary regenerator fluid is now involved, too. It will take longer for the engine to start producing significant power.

In an RSE the situation is somewhat different, because the notches are much bigger than in a SPARLVE. Please review the "RSE-60" link showing three lobes and notches per rotor. The group of sketches there shows the variant design where one rotor is 60 degrees out of phase with the other. But it is an RSE, a Rotary Stirling Engine, where only gas is the intended working fluid. The rationale for the large notches derives directly from some of the basic facts about all Carnot Cycle engines.

First, the temperature scale that is used for the Carnot Cycle must be an "Absolute" scale, where Zero degrees is "Absolute Zero", the lowest theoretically possible temperature (that's about -273 degrees on the Celsius scale). When the properties of most gases are studied using an Absolute temperature scale, it normally is observed that if the temperature is doubled, then the volume of the gas doubles, too, if nothing interferes. If the gas is confined so that it cannot expand, then its pressure will double instead. In a Stirling engine, the gas is partly confined, so that it must exert pressure on the power piston in order to expand.

The relevant question is, "How much is the gas volume allowed to change, in a Stirling engine?" The answer to that question tells us much about what the temperature-difference should be, between the hot zone and the cool zone of the engine. If the engine allows a 3:1 volume change, then it logically figures that the hot zone should be three times the Absolute temperature of the cool zone. So if we expect the cool zone to be room temperature, which is roughly 300 degrees on the Kelvin absolute-temperature scale, then the hot zone needs to be 900 degrees Kelvin, to make the gas expand its volume three-fold. A slightly hotter temperature may be useful in getting more power out of the engine (via increased gas pressure), but a much hotter temperature is likely to actually simply be wasted energy, because the engine can't properly use the greater changes in volume that would be associated with the higher temperature.

In an RSE the cooled gas gets pushed into a notch of one rotor. Even with large notches, compared to a SPARLVE, the space available is not especially great, compared to the space that the lobes of the rotors can traverse while being "pulled" by gas contracting in the cool zone, and in turn pushing that gas into the notch. A gas-volume change of 5:1 might be expected, perhaps. If so, this means that the hot zone should have five times the Absolute temperature of the cool zone, for an RSE to be maximally energy-efficient. That could be 1500 degrees Kelvin, which is quite hot, to be sure (approximately 2250 degrees on the Fahrenheit scale).

But, how quickly can we quintuple the Absolute temperature of a gas, and cool it down again? This is crucial, if we want an RSE to have a decently fast rotation rate. If we can't do it, then we need a smaller gas volume ratio in the engine--fairly easily done by using a different lobe size, relative to the rotor diameter and notch size. On the other hand, maximum efficiency of a Carnot Cycle engine depends on maximizing the temperature difference it employs! This trade-off between what is desired and what is possible is why a number of research engines would probably have to be built, to find the best compromise that we can engineer. (Now remember that in a SPARLVE, the typical 1000:1 ratio between gas and liquid phases allows smaller notches, a not-extreme temperature difference, and a possibly easier heat-transfer situation. That's why the author of this document tends to prefer the SPARLVE design.) Fortunately for any corporation not wanting to be annoyed with royalty payments while conducting such research, a corporation is legally a person, and making research-engine translations of this document can fall under the "free if built by self for self" clause of the Copyright notice.

Anyway, a regenerator can come in handy for an RSE, indeed! So please now see the "RSE-regenerator-1" link. Again a high-heat-capacity fluid is used, but this time its function is purely as a regenerator, and there are four fluid-travel loops (for any version of an RSE where each rotor has both lobes and notches; if the engine rotors are lobes-only and notches only, then only two fluid-travel loops are needed). The regerator fluid absorbs heat from the "displace" zone of the engine, as gas is rotated from the hot zone to the cool zone. Note that in the animated SPARLVE portrayal, it can be problematic to define where the hot zone ends and the displace zone begins. We obviously don't want a regenerator removing heat from the working gas before it has finished expanding and pushing on the rotor lobes! And that's (A) partly why the regenerator for a SPARLVE was chosen to be an indirect thing, and (B) why the version of the RSE that has triplets of lobes and notches on each rotor was portrayed in the "RSE-60" sketch: It possibly allows the different zones to be better-defined.

Nevertheless, that sketch also clearly reveals that there is still a significant problem with respect to trying to transport significant quantities of heat when space (gas volume of notch) and time (inversely proportional to rotation rate) are limited. (There may even be a slightly better layout for directions of fluid flow than presented in the diagram; feel free to experiment!) Certainly the first problem is why it was mentioned in the linked sketch that yet another variation of the RSE design is likely needed, to take full advantage of a regenerator.

You may recall that near the start of all these descriptions it was mentioned that the engine would feature at least two rotors. See the "Unfinished" link for a sketch showing an initial exploration of a 3-rotor design. It was also previously mentioned that I've been thinking about Rotary Stirling Engines for a long time, and that sketch relates somewhat to the prior descriptions in this document, and to an early effort, posted at the "Yet Another Heat Engine" link a few years ago, as well as to the new design at the "3-Rotor RSE" link.

Many variations on the generic theme of the SPARLVE and RSE, as presented here, are possible. It is in the author's best interest to mention at least one example of such variation, so how about an engine in which the rotors are not all the same size, or an engine with four axles/shafts for the rotors? See the "RSE-4-2" link, which shows both at the same time.

And now we are done with Regenerator stuff. The only remaining thing to discuss is a comment made early-on about pretending that 1:1 gearing is located behind-the-scenes, to ensure that the rotors stay properly/relatively aligned--and that the gears aren't really necessary. The simple explanation begins by asking you to go back and look again at the animated .GIF. It was constructed from 18 separate images, at 10-degree intervals of rotation. Suppose we had 18 rotors on each axle of the engine, and also on each axle neighboring rotors exhibit 10-degree phase angles. It should be obvious that in the overall assembled engine, no matter what its position in the total 360 degrees of one full rotation cycle, there will always be some of the rotors having lobes in notches, effectively acting as gear teeth. (18 rotors per axle is probably excessive, in fact.) Therefore no ordinary gears are needed.

Be careful when installing all those rotors in the same overall engine case, however! Some ways of doing it will lead to engines that cannot work! That will be because a pathway will exist for the working fluid to flow without exerting pressure on any of the rotor lobes! Either the rotors (or groups of rotors) on each axle must be isolated, in terms of fluid flow, or an installation pattern that resembles a "herringbone gear" will need to be used. Those statements are best explained with some accompanying sketches; see the "Offset Rotors" link.

The next sketch is at the "Gears" link; scroll down to the gears; both helical and herringbone gears are portrayed. But since gears have far more lobes and notches than are practical for this Intellectual Property, I've taken the liberty of severely distorting and modifying the herringbone-gear sketch, to try to show what the surface of a SPARLVE or RSE rotor might look like, with a lobe and a notch separated by nearly 90 degrees (okay, I admit my sketch isn't quite up to the intended result; they're more like 60 degrees apart. So?). See the "Herringbone Rotor" link.

In conclusion, if you imagine this rotor meshing with another, contacting where that central horizontal line would cross the front of the portrayed rotor, then one lobe is meshing at the center, and another lobe is either just-beginning or just-ending its meshing at the edges (depending on rotation direction). Therefore they can mesh well enough, for an entire rotation, to eliminate synchronizing gears (and their associated cost and energy losses).