NOTE: This copy of Making Stirling Engines is of the 3rd edi- Andy Ross - January 10th, . The V arrangement and the yoke drive (Ross linkage) are. Andy Ross recently started offering his book "Making Stirling Engines" as a free download. Andy Ross is one of the leading Stirling engine designers of our time, and But I was find another interesting places with pdf-files. versions of the engine for making the concept clearer. Some of the The Ross yoke drive, was first incorporated into Stirling engines by Andy. Ross of Ohio, a.
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Making Stirling Engines.pdf - Google Drive Stirling Engine, Google Drive. Visit ideas about Stirling Engine. Book by Andy Ross, linked to Stirlingbuilder. The factors that affect the success of making a successful Stirling engine in a An attorney by profession, Andy Ross in his book Stirling Cycle Engines. Stirling engines today - recent activities 20 .. Michael Rock and later Andrew Marsh provided helpful input and insights for the understanding .
Constructing a Stirling engine Background Information Attempt at making a Stirling engine Attempt to make a Stirling Engine Constructing a Stirling engine This research paper documents attempts at constructing a Stirling Engine with ordinary parts of glass and plastic found in a physics and chemistry lab. Three attempts were made with different methods of construction. All three attempts failed.
The paper analyzes why they failed. However simple they are in their making, Stirling engines are complex and intricate in their working. Page 5 of 48 Sahaj Umang Singh Bhatia 2. Introduction Stirling engines have long fascinated physicists and engineers for their efficiency and their ability to operate from any heat source. Screen clipping taken: , National Geographic There came my interest in Stirling engines and their known ability to convert heat into mechanical energy very efficiently.
The engine was invented in by a Scottish minister, Robert Stirling, long before the gasoline and diesel engines appeared. Stirling engines are more efficient and easier to operate but surprisingly, they are not widely used.
They also look easy to build and run to an amateur but keenly, as Jem and I realize, Stirling engines are much more than a simple assembly. Page 6 of 48 Sahaj Umang Singh Bhatia 3. Background Information 3. Stirling engines are engines which convert heat energy into mechanical energy by using the push created by the alternate expansion and compression of a working fluid which is enclosed inside the engine.
That means that the combustion process, which is the energy input to the engine, is separated from the working fluid which undergoes pressure and volume fluctuations to produce work.
Such external heat engines can be driven by any heat source, and thus prove to be useful anywhere where there is excess heat or any heat.
American Stirling Company
Stirling engines are unique in this context of engines, because their theoretical efficiency is nearly equal to the theoretical maximum efficiency of conversion of heat energy into mechanical energy , that is, the Carnot cycle efficiency.
Page 7 of 48 Sahaj Umang Singh Bhatia 3. The working substance is the gas that is transferred from one end of the cylinder to the other by a device called a displacer illustrated in blue. The displacer is a large piston that has a smaller diameter than the cylinder.
Its movement does not alter the volume of gas in the cylinder—it just transfers the gas within the cylinder. The four phases of the Stirling cycle are: Expansion Most of the gas in the system has just been driven to the hot end of the cylinder. The gas heats and expands, driving the piston outward. Most of it is still present in the hot end of the cylinder. Flywheel momentum carries the crankshaft the next quarter turn.
Most of the gas is transferred around the displacer to the cool end of the cylinder. Contraction The majority of the expanded gas has shifted to the cool end. It cools, contracts and draws the piston inward. Transfer The contracted gas is still near the cool end of the cylinder. Flywheel momentum carries the crank another quarter turn, moving the displacer and transfers most of the gas back to the hot end of the cylinder.
Page 9 of 48 Sahaj Umang Singh Bhatia 4. Attempt at making a Stirling engine 1 4. This cycle of back and forth movements will run the engine.
Boiling tubes 2 — 30ml 2. Syringes with plunger intact 2 - 20ml 3. Beakers 2 — ml 4. Rubber Cork 2 6. Quick drying Adhesive 7. A Cutter 8. Bunsen Burner 9. Wire Mesh Lab Thermometer 3 - oC Water- ml 4. One boiling tube will be in a beaker with water that is hotter than the water in the other beaker; i. Note the temperature using two lab thermometers. Cut one of the plungers from its other end to remove the holder of the plunger. Cut the other plunger in half and join both of them back to back with each other using the quick dry adhesive, so that it makes a two faced plunger.
The goal is to not allow any air leak this can be tested by wetting the barrel from the outside, if any water reaches the inner part of the barrel it means there is a leak.
That makes the piston part of the engine. Photograph 3- Stirling Engine 1 4. Page 13 of 48 Sahaj Umang Singh Bhatia 4. This way the pressure was building up inside the setup but it did not transform onto any work.
Only when there is some dimension in which the air can expand, will the air expand and put a pulling force on the displacer piston. Page 14 of 48 Sahaj Umang Singh Bhatia 5.
Attempt at making a Stirling engine 2 5.
The air that gets cooled due to the room temperature on the other end of the test tube will move the marbles back. The marble would move as a displacer. The glass syringe is 3 ml capacity, which has about 10 mm of diameter.
Five marbles has about The rubber cap is inserted the aluminum tube, which has 5 mm of outer diameter, 3 mm of inner diameter and 30 mm of length. The rubber tube has 6 mm of outer diameter, 3 mm of inner diameter, and 30 mm of length, and it must be soft. The size of the rubber seat is 36 x 15 x 2 mm. The both-faces-adhesive tapes, whose size is 15 x 15 mm, are pasted the both sides of the rubber seat.
The wood screws has 2. Nails are OK instead of the screws. The size of the base board is x 90 x 14 mm, and it is made of lauan wood. The size of the frames is x 30 x 14 mm. The size of the reinforced board is 90 x 30 x 14 mm. The big size of the rubber ring is better. The alcohol lamp is marketed. Although it fell short on its height, a wooden block was kept below it to correct that. Refer to Appendix 2 for detailed procedure as stated on the website.
Photograph 3 - Stirling engine2 5. In the video4 provided on the webpage, it is seen that engine works with little heat alcohol lamp and human interference. Photograph 4- Stirling Engine 2 5. The failure of this model is an important part of the whole research. It works on a principle different than normal displacer type Stirling engines or beta type Stirling engines.
The marbles are not part of the piston system of the engine, where the piston is pushed by increased air pressure inside the cylinder. They do not act completely as a volume displacer piston in regular Stirling engines but rather act as a heat displacer and to some extent as a regenerator, conducting heat from the hot side to the cold side. So when the mass decreases, the temperature difference should increase.
The measuring cylinder tilts and the marbles roll over to the other side. Now, when the marbles move to the side of the test tube above the flame, the mass increases in that area thus the temperature difference decreases. The marbles also absorb some heat from the air surrounding it and from the flame. According to theory the temperature difference should decrease, hence resulting in a pressure drop due to which the syringe retracts.
The retracting syringe tilts the test tube again, and the marbles roll over to the cold side. The cycle repeats itself and the heat from the flame, through the marbles, reaches the cold side and dissipates. Though work is being done by the engine by means of the up and own movements of the barrel of the syringe, but the movements are not smooth and cannot be reciprocated onto a crank to create circular motion by attaching with a wheel.
These assumptions were verified as false following the observations from the video and the second trial which, as earlier stated, made clear that the engine has a different working. A measuring cylinder was used instead of a test tube, as mentioned earlier, and that increased the mass as the measuring cylinder had a base made of thick glass. The snag here was the adverse effect that the marble mass had on the working of the engine. The syringe would have had to exert too much retraction force to tilt the test tube downwards, for which, the kind of drop in pressure level needed could not be generated.
Also the fact that the syringe extended very slowly, indicates that it was too tightly fitted and that would have also accounted for the non-retraction of the syringe. The air was unable to lose its heat rapidly, when after travelling to the cold side, and that is attributed to the thickness of the measuring cylinder.
It is very adequate to say that, the model would have worked with usage of standard apparatus it had required and, alternate equipment convoluted its methodology.
Page 19 of 48 Sahaj Umang Singh Bhatia 6. Attempt at making a Stirling engine 3 6. Air, taking in heat form the flame, will expand and push the two-faced plunger upwards, simultaneously creating push on the tightly fitted piston. The upward moving displacer will also allow some hot air to move to the cold space, and lose its heat. The total volume of the air inside the engine will increase but, volume on the cold side will decrease as the displacer piston, which is bigger, moves upwards compressing the air.
Here, the tightly fitted piston would be retracting back inwards, due to the compression, and therefore would push air and the displacer back too. Page 20 of 48 Sahaj Umang Singh Bhatia 6. The end of the barrel had to be cut to remove the melted plastic. Second Try Note: A water bath is used instead of direct flame.
This would fasten the process of heat loss from the air inside the chamber, when it travels to the cold side. The rubber washer on the plunger is taken out and another plunger is used, which is much smoother, with lesser friction.
Photograph Stirling Engine 3-Crack 6. A much paraphrased answer to that question is suggested, citing Dr. There are certain ratios of mass of displacer and piston and the net forces that act on them, which determine the pressure differentials required for a Stirling Engine to work that would have come into play Refer to 8. Conclusion , and further thermodynamic factors. These may have resulted in the problems faced in running the engine.
Attempt to make a Stirling Engine 4 Following up from the conclusion from Attempt 3 , a replication of a Stirling engine is constructed making use of another simple assembly available on the World Wide Web. Refer to Appendix 3. Care was taken to use the same equipment as stated in the instruction, so to avoid problems faced in Attempt 2.
Page 26 of 48 Sahaj Umang Singh Bhatia 7. Refer to Appendix 3 — Instructions Pg. Photograph Base of displacer being glued. Photograph The displacer rod inserted Photograph Soldered rod in the top surface of the displacer. This was possibly the only place where an air leak was possible, though it was negligible. Page 28 of 48 Sahaj Umang Singh Bhatia 7. This problem recurs but is corrected later by tightening the loop. An approximate rpm of more than 60 rpm is achieved.
This model was harder to build than the earlier models, but its working suggests that success of a successful engine indeed lies in replicating a successful model. Even though it had an observable air leak mentioned in 7. Page 30 of 48 Sahaj Umang Singh Bhatia 8. Conclusion Making a Stirling engine from scratch using uncomplicated tools and techniques and no sophisticated computer models proved to be simple but its success in working depended upon understanding the factors that can affect its construction.
Construction of a Stirling engine consists of not only what was done in the Research above but also the knowledge of heat cycles and thermodynamics involved. In this analysis, simplistic Stirling engines have been tried but there is a great possibility of research to be done about such construction of its Alpha and Gamma types and most importantly, using regenerators.
Though the Attempt 2 was also a replication of a successful model, its design differed from the expected and gave a chance of learning a varied type of process. Attempt 1 and 3 , stemming out of individual knowledge, contrastingly proved how unpretentious reasons initiate success.
Many such calculation were not possible to be done before making the engine, such as the pressure inside the chamber, which will in turn would have given the net force on the walls and the displacer. Citations from many sources mention such calculations and computer simulations that can provide with the perfect dimensions of a would-be perfectly working Stirling engine. Select an engine size that is appropriate for your uses and stick with it, developing it as far as possible.
Building prototypes of differing sizes is extremely wasteful of time, energy, and enthusiasm. It is the practical, not the theoreti- cal, problems of scaling that will prove the more frustrating. Pay great attention to mechanical details. Make sure the piston s seal well. Take care to keep friction as low as possible. Never be satisfied with binds or kinks in the mechanism. With the mechanical details done well, then one knows to look into the heat exchangers and burner for the answers to poor performance.
Take great pains to get the heat into and out of the working gas; you can never have too much active surface area, especially in engines charged with air. Become your own machinist.
It will get you quality parts on time, and encourage design simplicity. Or perhaps l should say, redesign simplicity. Countless times I have stood idle at my lathe, lazy as always, and mentally redesigned a complex part into a simpler one, before I could muster the enthusiasm to begin making it. Be on the lookout for subtle problems that can absorb incredible amounts of power, such as heater conduction losses or crankcase pumping losses.
Great patience is often required to solve these problems, and a little luck helps, too. Get your prototype out in the field for tests as soon as possible. It is the best pos- sible reality check.
Getting Started: The First Ten Years My active interest in stirling engines began in when I discovered the Philips literature and was inspired to design an air-charged stirling of several horsepower for use on a bicycle.
The project was expected to take about a year. My initial design was a complex mess, featuring twin double throw cranks, scotch yokes with rollers, twin cylinders, and a novel speed control system with several valves and passages upon which I had recently obtained a patent. After many more months of effort, this new engine was finally ready for its initial test run.
Unfortunately, even with the heater tubes glowing bright red from the heat of a propane torch, the engine would do nothing more than turn six or seven feeble revo- lutions at a time, and then stop. This engine was to be a quick project that would be completed in one month and would raise my sinking morale. It actually took five months of spare time to complete, and it, too, showed no serious inclination to run. So it was that I spent two years of quite considerable effort in reading the stirling literature and designing, machining, and building engines, and yet was still unable to get an engine to run, let alone produce any useful power.
I was now obsessed with the idea of the modern stirling engine, per se, and I was determined to have the satisfaction of seeing one of my engines run. To that end, I wrote to Ted Finkelstein, to obtain the benefit of his wisdom.
In his kind response of August 1, , Dr. Finkelstein wisely suggested that I go back to the basically sound rhombic design, eliminate the complex valved speed con- trol mechanism, and modify the heater to minimize thermal losses. The new heater also eliminated the excessive internal dead volume associated with the original tubu- lar heater. Below, the V-2, based on an automo- tive freon compressor. The 65cc rhombic in the form in which it first ran.
In all other respects the engine was left as it was, since mechanically it was already quite good.
Its friction was low and its seals were excellent. One unusual feature of the design is a displacer bore 2. With these changes, the engine ran on its first attempt, in late January, At that time, it had no proper burner, but was merely heated by a hand held propane torch.
Nor did it have any regenerator matrix. Despite these handicaps, the engine qui- etly turned rpm, and I was quite happy. It took alittle over a month to build an annular ring burner with a single row of jets and a rather crude prony brake. When these accessories were at last operational, I was shocked to learn that peak power was a mere 1. With a 0. The gap inthe rhombic was 0. Performance improved to 3.
Next, I tried fine steel wool as a regenerator matrix, and power jumped to 7 watts, atmospheric, and 9 watts at 2 bar. By the end of April, , the engine had produced Even then, only a small portion of the heater head was even at a dull red heat. It was obvious that a great improvement in both speed and power would be available when a burner could be devised to keep the entire heater glowing bright red. At this point it seemed reasonable to concentrate on improving the burner.
What I did not realize was the magnitude of improvement available when the ratios were right. This knowledge came as I experimented with a set of interchangeable orifices I had made, each with a slightly different size of hole.
I was used to rather mushy dark blue flames issuing out ofthe burner jets, which would barely turn the adjacent heater head a dim red in low light when the engine was not running. Most of the ori- 13 The 65cc rhombic with its first burner on an early brake above , and in its present form left. But upon trying one of the smallest orifices, the burner immediately changed its entire personality.
In the first place, it was cranky and hard to keep lit when the engine was cold a variable mixture control later solved this problem. The jets would ignite and go out in a circular pattern around the burner. As the heater head became warm, however, the burner stabilized nicely. Instead of the mushy dark blue flames I was ac- customed to, the jets were now producing hard, bright blue miniature torch points. And they were no longer silent; they produced a sort of sizzling sound.
Best of all, the narrow strip of heater adjacent to them glowed bright red. At once, the answer to the burner problem seemed obvious. Simply stack four or more rows of jets into a burner, and find the right size orifice and mixer tube. Several new burners were made along these principles, and each one boosted performance. With the last burner, made in , the engine pro- duced 32 watts at rpm, atmospheric; 66 watts rpm at 2 bar; and The engine under the burners was relatively unchanged.
A great deal of what I learned on this engine was qualitative, rather than quantita- tive. For example, on various occasions the engine was running on air, and then helium was introduced into it. In the darkening heater one could actually see the improved transfer of heat into the engine. Interestingly, helium has little apparent effect on later prototypes with extended surface area heaters, since they already have good heat transfer with air. One early improvement was afinned aluminum alloy cooler, which achieved a substantially increased surface area over the original drilled cast iron cooler without any increase in dead volume.
I was surprised when performance remained unaltered, but later realized that the engine was heater-limited, not coolerlimited, so the superior cooler could make no difference until the heater was improved. Tests were conducted on various regenerator materials, including steel and stain- less steel wool, woven and wrapped stainless wire, ceramic wool, and dimpled stain- less foil.
The stainless steel wool had numerous small particles that broke away and got into the heat exchangers. The ceramic wool broke down completely and was blown throughout the engine.
The woven stainless wire and foil were the most promising, with the foil moving the peak power up to a slightly higher speed. I was seeking breadth of knowledge rather than depth, simply because there was so much interdependent territory to cover.
This 65cc rhombic truly was the workhorse of the first 10 years of my stirling work. It has run numerous hours on minimal lubrication without giving any trouble; and, indeed, is still doing so as a student test engine at Ohio University.
During these early years l was actively corresponding with, and meeting, just 15 The 11cc rhombic above , and the cc rhombic left. The value of such personal contact cannot be overstated. Not only is information shared, but also morale is sustained.
Stirling engine development, like any other creative work, can be lonely, frustrating, and difficult. But if the small triumphs that occur and provide such satisfaction are shared with others active in the field, then all can continue their work with a better spirit.
Other Rhombics The relative success of the 65cc engine inspired a series of other rhombic designs, some actually built, others not. Among the engines actually built was a small 11cc demonstrator engine designed for an article in Model Engineer magazine. This engine employes exactly the same rhombic geometry as the 65cc engine, but scaled-down to half size. The piston is cast iron, machined to a close clearance about 0.
The displacer does not seal against the cyl- inder at all, but rather has 0. The engine ran well from the start, producing 8. The entire project, including the article resulting from it, consumed only a month and a half to complete. A second rhombic was a cc engine intended to be the successor to the origi- nal 65cc machine.
It incorporated quiet delrin synchronizing gears, internal aluminum bronze heater tins, a separate pressurizable butter case, and clearance seals. However, the internal cross sectional area of the heat exchangers was too restricted, and the press fit between the heater wall and the internal fins produced an inadequate thermal bond, consequently initial performance was mediocre.
At that time I was so very impatient to move on to such new ideas as the yoke drive that I simply abandoned this engine without any development whatsoever. Looking back on this episode, I am struck by my seemingly unlimited energy and enthusiasm, and how readily I squandered them. I would also note that the cc was too different from its 65cc predecessor; it was indeed a new engine in almost every respect, with all the headaches that entails.
A far better approach would have been to modify the 65cc engine one step at a time, so as to learn what was an improvement and what was not.
A third rhombic was a cc test engine built under a DOE appropriate technology grant to make a simple, low pressure, high speed hot air engine of watts output. Although much larger than the 65cc rhombic upon which it was based, this engine was very much closer to that original engine in design than was the ill-fated cc machine described above.
The DOE engine used off-the-shelf piston rings re-machined for lower outspring and friction , a plain annular heater with inner sleeve, and a greatly larger bore 4. It produced Testing under 17 pressure was attempted, but was unsuccessful since the crankcase cover distorted un— der pressure, causing excessive shaft seal friction.
By this time the grant funds had run out, and the balance of my effort on this engine was devoted to demonstration on a wood stove. This large rhombic presented few problems, other than finding the proper end gap for the rings, and the proper mixing tube and orifice diameters for the propane burner under which the power testing was conducted. There were signs that the friction could be further reduced, and the sealing improved, and I believe with more develop- ment time this engine would prove to have considerable potential.
On the other hand, it was at the upper size limits of what could comfortably be made on my machine tools, so I did no more with it and eventually sold it to the University of Calgary. During this DOE work, it occurred to me that the rhombic drive lent itself to use in a low pressure pancake-shape engine. Several new versions of both the 65cc and the 11cc engines were designed along these lines, and overall dimensions were significantly reduced. A 1 10cc version of the 11cc engine was begun, featuring a 4 inch Overall height would be a mere 5 inches Even with an unfinned heater, there is sufficient surface area to produce watts output, charged with air at atmospheric pressure.
Al- though never completed, I still believe this design represents an excellent way to make a simple, compact, high speed, low pressure stove-top air engine.
Below is a sectional view of the cc rhombic. I cer- tainly understood that it had a great deal of unrealized potential, even as I moved away from it. An extended surface area heater, additional regenerator volume, increased working pressures, anti-friction bearings on the connecting rods, and other more or less obvious modifications would all have substantially improved its performance. But there was too much I still did not know about other types of stirling to let me comfortably settle on one design for development.
At this point, I had become more interested in exploring new ideas than in developing a practical engine. The first attempt to see if a simpler approach might work as well as the rhombic drive resulted, in the Spring of , in a 38cc V-2 gamma type engine, which incorpo- rated the existing displacer dome, burner, heater, and regenerator of the 65cc rhombic.
This new engine was quite easy to make, and it had excellent dynamic balance. Fortunately, before too much effort was wasted in this enterprise, comparative thermal efficiency tests were conducted which showed the V-2 to be less than one third as efficient as the 65cc rhombic.
Excluding stack losses and heater head radiation losses, the rhombic showed I suspect the low compression ratio inherent in the gamma type engine effectively mag- nified the deficiencies of the regenerator, and was the main cause of these poor thermal efficiencies. In any event, my enthusiasm for the gamma type engine faded rapidly with this knowledge.
A second and more successful attempt at simplicity was a 15cc alpha engine com- pleted in November It featured simple annular heat exchangers like those used inthe 11cc rhombic, and very close-fitting cast iron clearance pistons running unlubri- cated in honed steel cylinders. Other than the care required in machining the piston-to- cylinder fits, the engine was extremely easy to make.
What a delightful surprise to start this engine and have it run faster and faster until it reached rpm, far faster than any stirling I had built up to that time. Like the 65cc rhombic, this little alpha engine became a testbed for various modifications, such as a tubular heat exchanger system, a variable dead space speed controller, and a new yoke drive mechanism.
As the phase angle increased, the engine became more docile, easier to start, more of a low temperature engine, with lower compression and power. Although all of these differences could have been antici- pated by theory alone, to experience them first hand in a real engine was most satisfy- ing. Another interesting test was a power comparison between the small rhombic and the alpha that Jim Senft and I conducted in Athens, Ohio, in May These engines had similar expansion space volumes, and I expected similar outputs using the same burner.
But the alpha produced only 6. Ini- tially, I attributed this difference to some inherent superiority of the rhombic drive. The Yoke Drive The success of the small alpha produced a burst of activity. The 15cc alpha engine was immediately modified to incorporate the yoke drive, and it performed as well as ever, but not noticeably better, as I had hoped it would.
By January of I had begun a 50cc yoke drive engine that would employ the existing insulation dome, heater, regenerator, and burner of the 65cc rhombic.
After the discouraging activities with the gamma engine, I needed some promising new path to follow, and the yoke drive seemed to be just that. The yoke drive consists of a triangular yoke mounted on a single crankpin, and guided by a rocking lever.
The combination of the circular motion of the crankpin and the arc of the rocking lever produces nearly linear motion at the extended arms of the yoke, with a phase between the motion very suitable for an alpha type stirling engine.
The three major advantages of this drive mechanism are: 1 very low piston side loads, permitting long life and low friction with oil-less operation, 2 closely spaced parallel cylinders, which are easily connected with compact heat exchangers, and 3 relatively small size and low weight for a given swept volume.
The use of a single counter—rotat- ing balance shaft will put the engine in complete primary balance, or, the engine can be partially balanced without the extra shaft if some vibration can be tolerated. During the construction of the 50cc yoke drive engine, I was sure that I had finally found a way to make a simple stirling that would perform well. When it was finally far enough along for an initial test, I wasted no time.
The engine was fired up, and when the heater was red I flipped the flywheel. The engine ran, but rather slowly.
Making Stirling Engines
It built up speed, but again rather slowly. After what seemed like 5 minutes, but was more likely only several minutes at most, the engine still did not seem to be performing well at all. The compact Inverted Yoke Drive.
The Cable-Driven Yoke Drive. The Rocking Piston Yoke Drive. Wax die for cast heater head. Type ss cast heater head. Diversions A period of extended disillusionment followed this brief initial run of the 50cc yoke drive engine. My stirling work continued, however, and considerable time was spent thinking of ways to create extended surface area in heaters. Eventually, I decided to at- tempt an investment cast, externally and internally finned, stainless steel heater head.
After overcoming the usual unforeseen difficulties, several successful multipart alumi- num dies were made to produce the wax patterns necessary for the casting process. To my dismay, the internal fins of the patterns, being 0. These parts were eventu- ally successfully and consistently cast by another firm using vacuum investment and a newly developed ceramic. Indicative of my sagging morale at the time, however, this successful work was never followed up by actually testing one of these elegant heaters on an engine.
Another project undertaken during this period was a machine to dynamically test gas flow losses through heat exchangers. This machine was painstakingly designed and constructed, and then, for lack of interest, never used and eventually scrapped. While demonstrating the 15cc alpha engine for him, I noticed that it seemed to take a longer time to come up to speed than the rhom- bic engines.
Given a chance to properly warm up, the 50cc alpha showed very promising performance, with a free speed of rpm. I quickly built a balance shaft for the engine, and thereby confirmed that the patented balance scheme worked.
My enthusiasm for stirling work was restored. It occurred to me that a general purpose stirling engine could be designed and usefully sold as a kit in an effort to encourage more people to get involved with stirling engine development.
The 50cc engine was obsolete in various ways, so a new engine was designed from scratch, incorporating everything I had learned about stirlings over the years. The resulting engine was a 35cc alpha yoke drive engine that was without doubt the finest stirling engine I had designed.
The heater and the hot pistons insulation dome were stainless steel deep drawn cups, available commercially as cases for electronic devices. The heater was of the simple annular gap type. The regenerator was wound of stainless steel foil, 0. The cooler consisted of water-cooled slots cut into the cylinder head, connecting the compression space to the plenum beneath the regenerator.
The pistons were of the clearance type, made of thin-walled cast iron, running in honed steel cylinders. Performance was very good from the start. On the first power test the engine produced 21 watts at rpm, atmospheric pressure. After the snifters were added to the crankcase and the workspace, peak power atmospheric increased to 28 watts. Brief tests at 0. Maximum free speed at this time was rpm. The cold piston subsequently seized, and the cylinders were honed out a bit more.
This time clearance was sufficient to permit a smear of light oil to be used as lubrication without 32 excessive drag. Free speed moved up to rpm, and power increased to On tear-down, further signs of piston rubbing appeared, so additional cylinder metal was honed away. Free speed jumped to rpm, and peak power went to These results were extremely gratifying.
This engine was substantially smaller, Iighter, faster, simpler and more powerful at a given pressure than the 65cc rhombic. I undertook my first field test with any stirling, by incorporating the engine in an outboard rig made from copper tubing, a suitable synchro drive belt, and a Sears plastic trolling-motor propeller.
This device was mounted on a 17 foot canoe, and tested on the nearby Scioto river. After 25 minutes of cruising, a portion of an epoxied-on water jacket fell off, stopping the flow of cooling water and allowing one ofthe pistons to seize. The field test was both great fun and instructive. The water jacket that had so easily come loose in the jostling of the field test had given no problem in hours of prior bench testing.
Putting this engine in kit form took much longer than anticipated. About 50 kits were sold, but it soon became clear that most first-time stirling engine builders needed something much simpler. For this purpose, a V version of the old 15cc alpha engine was developed.
This engine, called the V, was popular, and it makes a very quiet and im- pressive demonstrator engine. Some builders were still having problems machining the proper piston-cylinder fits, however, so it was replaced with a 20cc yoke drive engine, the B, which had removable cylinders that could be more easily refinished if neces- sary.Alpha engines have two pistons in separate cylinders which are connected in series by a heater, regenerator and cooler. Constructing a Stirling engine Or perhaps l should say, redesign simplicity.
Philips Company were looking for a simple, reliable, and long-living engine to generate 10 to 20 watts of power for their radio receivers in remote regions where central station electricity was unavailable.
Its movement does not alter the volume of gas in the cylinder—it just transfers the gas within the cylinder. The total volume of the air inside the engine will increase but, volume on the cold side will decrease as the displacer piston, which is bigger, moves upwards compressing the air. The combination of the circular motion of the crankpin and the arc of the rocking lever produces nearly linear motion at the extended arms of the yoke, with a phase between the motion very suitable for an alpha type stirling engine.
NOTE: This copy of Making Stirling Engines is of the 3rd edi-
An LTD Stirling engine is efficient enough to run from the waste heat that is discharged from other appliances or from the warmth of direct sunlight. This large rhombic presented few problems, other than finding the proper end gap for the rings, and the proper mixing tube and orifice diameters for the propane burner under which the power testing was conducted.
Substantial additional reductions in engine height could come from using disc pistons with tail rods guided from below, as shown on the schematic drawing of the cable-drive system, above, but such pistons would require an excellent line not clear- ance seal.
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