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Forum Index : Solar : Solar Steam
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| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi All A few comments on increasing the efficiency of air conditioning have been made, and just to throw in my 2 bob,s worth. On a split system instead of running the pipes through two insulated sleeves I found that running them in the same sleeve helps by further cooling the high pressure line to the evaporator using the cooler residual temperature of the return line, not rocket science but it works. I noticed ice forming on the return line and thought how I could recycle the cold that was being wasted on the outside atmosphere. Water is to precious and contaminated with naturally occurring minerals to use on systems not designed to handle the contamination. All the best Bob Foolin Around |
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GreenD88 Senior Member  Joined: 19/05/2009 Location: United StatesPosts: 104 |
I would have that system checked out by a professional, Sounds like you were low on refrigerant or you wasn't transferring enough heat from the evaporator to the refrigerant if the return line was icing up. Running the lines in the same insulated sleeve should only be done on a properly charged system as a last resort to raise the superheat to the correct point unless the system was designed for it(it's called subcooling). On a properly operating system doing this will raise the superheat too much and actually cause less cooling of the compressor and eventually cause compressor damage. Licensed Master Plumber / EPA 608 Universal License / 410a Safety Certified / Medical Gas Brazer/Installer |
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Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Tim C Moving away from the refrigerant/air conditioning discussion for the moment, I have had a look at the link that you gave for Jeremy Holmes and his Otto 4 cycle "flashing" steam engine. I will admit to being somewhat confused as to what he has accomplished here. His part 3 animation shows an engine that has heat energy being supplied to it through heating of the cylinder, and through superheating of the intake steam, and possibly also through heating of the injected water, although the amount of heating here is not clear. I think that I recollect his injector system as needing 200W to operate? That part of the exhausted steam that is not re-cycled through the engine appears to be condensed, with any remaining steam exhausted to atmosphere. There would therefore be heat lost through the condensor, plus what heat remains in any exhausted steam. I would be very interested indeed to see some efficiency figures, comparing total heat energy input, plus mechanical ane electrical energy input, with the net mechanical energy output. This would show if the set-up has achieved anything significantly better that the more conventional steam engine arrangements that might hit 20% or so if they are really working well. Regards Don B |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Greend88 OK on the remark re the pipes , My friend who is an engineer in commercial refrigeration is the one that suggested it and then helped me do it, he said it was to overcome something wrong with the Chinese split systems as I only have a basic knowledge of air conditioning I took his word for it, So far it works OK and if it does kill it it will give me an excuse to replace it with a better one, the new split systems with inverter drive ear 30% more efficient he tells me so less power draw and that's good. All the best Bob Foolin Around |
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tim c cook Newbie  Joined: 02/06/2010 Location: United StatesPosts: 11 |
Don B - 4-cycle engine - The "4-cycle" reference is to the different methods he is using to push the piston down. It does not recerculate part of the steam and expel the rest, it does one or the other but on different strokes. The first input is the superheated water injection, it is injected with both intake and exhaust valves closed, this water is at something like 1000 deg f and under high enough pressure that it does not boil until it is injected into the lower pressure heated cylinder, there it flashes into vapor and drives the piston downward, as the piston starts it's upward exhaust stroke the steam vapor is directed out of the cylinder's mechanically opened exhaust valve and into the upper steam reheater, the piston also compresses the vapor inside the reheater causing the steam temperature to rise even more, once the piston reaches top dead center the mechanically operated exhaust valve closes and the intake valve opens, the recycled and reheated steam is now admitted back into the cylinder to produce power on the second piston down stroke, once the piston starts back up the now mostly spent steam is directed out of the cylinders mechanically opened exhaust valve and directed either to a condenser or to the atmosphere (not sure here, didn't study the system that closely). The exhaust valve closes and the superheated water is again injected in to the closed cylinder - on-n-on. The concept of adding heat to the cylinder jacket and the reheater allows the system to operate without a separate boiler, the cylinder acts as the boiler directly to add heat to either the flash steam vapor during the 1st piston cycle or to the recirculated recycled steam vapor during the 3rd piston cycle. I have another university grad paper that also used this heated cylinder method with frig fluid, by using the working fluid as a liquid rather than vapor it eliminates tha seperate boiler and also allows you to use much smaller diameter fluid supply lines and injection device. This approach of using flash vaporized liquid working fluid into the cylinder might have allowed you to use your original idea of using a gasoline engine fuel injector? Using high pressure water requires the heavy-duty custom liquid injector valve due to the high pressure required to keep the water liquid but it may be that the much lower pressures found using some Organic Rankine cycle frig fluids would allow using the gasoline engine injectors? (maybe not, from reading, apparently they don't open reliably at input pressures above something like 100 pounds pressure on the fluid?, depends a lot on which style injector they are, the single pintel injectors apparently open under higher pressures than the multi-hole or disk type.) In your original testing using the engine injectors what size (flow rate) injectors were you using, they are available in many different flow rates from tiny to huge, listed in "pounds per hour" based on the weight of gasoline. The rated PPH flow is based on them being held open continuously at a pressure of 55 PSI (from memory, at least something close to that pressure) so you would have to figure the duty cycle to get the actual flow, plus the expansion factor from liquid to the flash heated vapor volume/pressure. I intend to eventually do some opening pressure testing of gasoline engine fuel injectors, I have collected a few different flow rate injectors to try but don't have any of the really large flow rate ones yet. I am still thinking about this method using the York uniflow style engine concept, this would make a REALLY simple engine that should be capable of high rpm, also simplify the total system a good bit, with enough condenser area it might even operate without a fluid feed pump (liquified 100 deg propane will still be under at least 100 pounds pressure to push the liquid through the injector into the lower pressure of the engine's cylinder that had just exhaused it's spent vapor. (probably will still need some sort of liquid feed pump to the injectors though, the pressure of the exhausted vapor into the top of the condensor will likely be close to to the same pressure of the condensed liquid at the bottom of the condensor, especially with a uniflow engine. If using a in/out spool valved engine the exhaust stroke could produce a lot higher vapor pressure into the top of the condensor but this would likely lower the engines's rpm capability, may be worth the trade off though?) There is a small 3-4KW ORC system that runs without a feed pump but they use gravity from a tower to create the pressure to push the condensed liquid back in to the boiler. (seem mainly to be soliciting investors rather than actually supplying systems) This is a link to there web page, they are now using a small turbine but there original testing was with a converted 2-cylinder air compressor engine using a custom chain driven rotary valve. http://www.sterlingsolar.com/ (not sterling engine, different, name of inventor) |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Tim C Still a bit confused about what Jeremy Holmes engine does. The text associated with his diagram says that the exhaust steam is open to the atmosphere via the condensor, so that I imagine that the intake stroke must draw steam through the re-heater and into the cylinder. This could not be a power stroke, as there is no pressure in the steam (apart from atmospheric) at this point. The subsequent compression stroke heats the steam both by reducing its volume, and as a consequence of the external heating of the cylinder. When the hot pressurised water is injected, its flashing is no doubt helped by the hot steam already there. If water was not injected at this point, I guess that the heat picked up by the intake steam from the cylinder would provide a feeble power power stroke. The advantage of injecting water instead of steam into the cylinder is that you get a large volume increase as the water flashes. I don't know what the water to steam volume ratio is at the pressure his engine operates, (at atmospheric pressure it's 1,600 to 1), but it would certainly mean that he has much less volume to deal with than if he was trying to admit the same volume as steam. This, of course, is the problem that I am grappling with, in trying to get a fast response from a steam solenoid with a big enough orifice to admit a useful steam volume. For all that, Jeremy's engine still looks like a classic 4 stroke Otto cycle to me. On the matter of injectors, I did find a US site that had performance tables for fuel injectors, but I can't find the hard copy now. I am sure that an internet search would find it. I also ran across the US Clean Air Power site that may have some interest for you. Regards Don B |
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| danielhenry31 Newbie Joined: 29/06/2010 Location: United StatesPosts: 5 |
Steam is a lot of opportunities for the adequacy of small power sources. I had plans for a small plant that produced 700 watts, removes a fireplace built in low-pressure boiler and condensing engine to operate at a difference of 30 pounds. At 24 hours of operation which provided all the necessary power and hot water for a family home of 32-volt system, there are more efficient appliances available now so it would be a success in cold climates. portable battery charger |
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| JeremyH Newbie Joined: 31/07/2010 Location: Posts: 1 |
Hi All, If you have any questions about the 4-cycle steam engine, I would be happy answer. The main advantage of the engine cycle is that it does not use a traditional boiler, thus simplifying boiler controls. It is a flash steam engine so all the steam is made in the cylinder. The current model of injector im working on is the S08 model which is a miniaturized version of the L912 model. Im hoping to cut/reduce power consumption with the new model. The L912 injector does handle very high pressure supercritical water. The S08 only handles hydrostatic pressure, meaning the water does not contain supercritical energys. Although the the pressure should be at or above 2000psi, in order to get enough injected water into the cylinder at speed. Its possible to get away from injecting supercritical water using superheated low pressure steam aspired into the engine, this contains enough latent energy to get the injected water to "flash". Also the engine cylinder head, upper portion of the cylinder, and injector body is heated with heat transfer fluid(oil) its not pressurized. The first running prototypes used supercritical injected water, which was scary to be around. My goal is to make a user friendly steam engine, and thats were the superheated low pressure steam comes in. Best Jeremy |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Since my last post was a few months ago, I thought that it was about time for an update on my Briggs and Stratton steam engine. Unfortunately, my Wife is a keen gardener with 30 acres to range over, plus I am doing a major house renovation, so time for the steam engine or any other hobby type things is in short supply. I have run the engine on compressed air at up to 800 rpm, but have had some problems with the solenoid control electronics. These have been occasionally missing the No 1 cylinder 360 degree "z" pulse from the shaft angle encoder, which throws the solenoid timing out and stalls the engine. I have also realized that it needed more air in each cylinder, so now have twin solenoids per cylinder. The present counting circuitry uses three 4029 IC chips counting up in binary to 360 degrees, where the z pulse from the shaft angle encoder then resets the counter by loading it with zeros to re-start the count. The count is decoded by a series of gates to give a pulse output at a range of angles that are used to turn the inlet solenoids for each cylinder on and off. Unfortunately, each angle that is decoded from the 9 bit output from the counter involves 3 quad gate IC's, so the range of angles that I decode has had to be limited. For each of the three cylinders, I can access angles at -60, -40, -20, -10, and 0 degrees (top dead centre) for advance angles (ie to turn the solenoid on), and +60, +80, +100, and +120 degrees for admission angles to turn the solenoid off again. This adds up to a lot of ICs and, while it works well enough, the whole system is totally dependent on getting the 360 degree pulse to reset the counter at the correct point. If it misses a reset pulse it stops. I have been thinking of ways to get a back-up reset pulse by using an optical sensor to read a mark on the flywheel or, alternatively, using a pulse from the original LT ignition points on cylinder 1. To use the existing points, the most precise action that I can use is when they close, rather than when they open, as one contact of the points is the original capacitor, and the open point will not be an immediate rise in voltage, but will follow the capacitor charging curve. The points close at 305 degrees shaft rotation, and open again at 350 degrees so, to generate a pulse at 360 degrees, I need to count 55 degree pulses on from when the points close. This is certainly possible, but the complexity starts to make the optical sensor much more attractive. Incidentally, the flywheel has two magnets cast into it for the original spark magneto, but the field from these is too extensive to get a sufficiently accurate and repeatable pulse from a hall effect device, and you also get two pulses per rev. I have also come to realize that I could get solenoid open and close angles down to degree accuracy if I used some further 4029 ICs in down counting mode with the initial count binary pre-load obtained from a Picaxe micro. Angle selection to degree level is what I had originally intended, until I found that a Picaxe is way too slow to perform the actual count and decode itself at 10 kHz. Unfortunately, using down counting means that I will have to scrap the existing count up and decode boards, which contain about 50 ICs, and replace them with new boards with about the same IC count. As Malcolm Frazer, one of our past Prime Ministers said, "Life was not meant to be easy". I will post further progress (when there is some). Regards Don B |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Don Sound like you are having fun and games with the engine, I thought the control was to symplify the timing process but from the sound of it, its a bit of a worry to non electrical person like me. I like the solinoide approach but the electronics to go with it is a worry, Murphy states that things fail at the square of the number of the components, and Gyberson's law states that Murphy is an optimist. Best of luck with it and I awaite thee outcome. I did some checking on the solinoide situation and the multi approach is the way to go, then you have the option of using the number to regulate the power output by switching more in as the load increases. All the best Bob Foolin Around |
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| tim c cook Newbie Joined: 02/06/2010 Location: United StatesPosts: 11 |
I am still playing with this concept, the idea now is to use a 2 cylinder outboard motor power head as a uniflow expander engine by feeding liquid frig fluid into the top of the cylinders (sparkplug holes) through solenoid operated hydraulic valves, the normal cooling water passages in the engine will flow HOT water to help expand the liquid into as much vapor as possible for each cylinder stroke. I recently picked up an old 1952 Scott-Atwater 10 HP outboard motor for $15.00, it has a bore of 2.1 inch and a stroke of 2 inches so is just a bit bigger than the York frig compressor. The idea is to block off the exhaust from the cylinders and use what were originally the INTAKE passageways up from the crancase as the exhaust outlets, this will flow the vaporized frig fluid, and any oil it contains, down across the roller and ball bearings of the connecting rod lower ends and the crankshaft, weather this will provide adiquate lubrication to the bearings has yet to be deturmined. The cylinders of this old junkyard engine are a bit rusty so I am still doing an electroplate type de-rust on the engine and have not yet done any actual testing. Researching hydraulic solenoid valves I have found a couple "Hydroforce" brand 12 volt DC on-off valves that look promising. one flows .5 gallon/minute and takes 16 MS to open to 80% flow and 10 MS to completely close, the orifice is stated as .032 inches. The next larger valve flows .9 G/M and takes 22 MS to open to 80% and 5 MS to close, no orifice size is given. There are others. These valves are rated to 3000 pounds pressure so the flow rates may be at that pressure, if so, a valve with a larger orifice opening will have to be selected for the lower pressure of this system, A larger valve will likely operate slower? The .5 G/M valve is here - http://www.hydraforce.com/Solenoid/Sol_html/1-080-1_SV08-26/ 1-080-1_SV08-26.htm The .9 G/M valve is here - http://www.hydraforce.com/Solenoid/Sol_html/1-081-1_SV38-26/ 1-081-1_SV38-26.htm This links to the 2-way poppet valve selection page - http://www.hydraforce.com/Solenoid/Svppbl2w.htm Click "products" to see all the available valves. |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
tim c cook Have you stopped to consider how a 2-cycle internal combustion works? Down inside each cylinder are "ports" (holes drilled through the cylinder wall into the surrounding "air box") which allow pressurized air-fuel mixture from the air box to flow into the cylinder as the piston starts the compression stroke. The piston then compresses that and the spark ignites it. Once past top dead center, the hot expanding gases exit through the same ports. On the return cycle, it does the same thing all over again. My point is, how are you going to recapture your now-expanded refrigerant? Surely you're not intending to let it flow freely into OUR atmosphere as that would be a no-no. If you're using steam as a working fluid, there is no problem. A uni-flow engine is extremely fast and more effecient than other methods, but it will consume a ginormous amount of steam. I know, because I've built and run several in my life. If it were I, I'd spend a little more time investigating the basic mechanics of this thing before spending oodles of money on fancy valves. By the way, a "rotary" inlet valve is the usual method used for this type of contraption and that is something you can whip out on a good lathe in about the time it takes to brush your teeth. It's merely an anular groove conneted to a flat spot on the main crank. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Solenoid Inlet Valves for Engines 3rdJuly, 2011 Hi Tim, I am working away from my office at present, so don’t have access to my Back Shed log in to post this directly. It will therefore have to sit as a Word document till I dig it out. My 3 cylinder Briggs and Stratton steam engine with solenoid inlet valves is still in development after a long time spent re-designing and rebuilding the control system. I have now ironed most of the bugs out of it, and have the engine running reliably on compressed air at up to 900 rpm. This is still short of my ultimate target of 1,600 rpm, but close enough to my plan B, which is to get to 1,100 rpm. I am happy to settle for that. I plan to send some details to this thread on the Back Shed forum once I have completed optimising and recording the control system settings. My new control system lets me adjust the advance angle at which the solenoids open to any number of degrees before top dead centre for that cylinder, and to separately adjust the number of degrees through which the solenoids remain open. This adjustment can be selected to be manual or automatic. In an effort to reduce the 10 ms opening time of my solenoids, I use pre-energising to build the field to a value just below the minimum current needed to open the solenoid at any given manifold pressure up to the design maximum of 100 psi. I can now readily alter this value with the engine in operation so that I can plot the precise maximum that I can use before the solenoids open prematurely. When I need the solenoid to open, I provide it with a short (somewhere around 3 ms) full rated or over-voltage pulse, and then reduce the current to just above the minimum hold open current. This allows most of the field to dissipate, and helps to shorten the close time, which otherwise could be around 5 ms. Interestingly, the hold open current is fairly much independent of the manifold pressure. I can now readily change the full voltage pulse time and the hold open current, again while the engine is running, so am also accurately optimising and plotting these values for the range of engine speeds. What I have found to this point is that it is essential to be able to change the advance angle at which the solenoid opens as the engine speed changes. At present, I start with an advance angle of only one degree or so at zero speed, but need to increase the angle to around 70 degrees at 900 rpm. If the advance angle is not linked to engine speed, then the engine does not perform well. The angle after opening through which the solenoid is held open is around 100 degrees at start, and reduces to around 40 degrees or less as the engine speeds up. I am still experimenting to plot the optimum opening angle for various speeds. I have found that keeping the solenoid open for more than the optimum opening angle actually slows the engine down. This is probably due to the fact that, by bottom dead centre, there is still pressure on the piston, even with the exhaust valve open, and it resists the upstroke. The engine now has a pressure transducer for each cylinder, and I can see the arrival and shape of the pressure pulse during each cylinder revolution. This also permits me to compare the pressure pulse in each cylinder, which can flag mal-operation of the timing circuitry, or the solenoids themselves. I am still looking at the relationship between the timing of the electrical opening pulse and the arrival of the pressure pulse. As you would imagine, the pressure pulse arrives a finite time after the solenoid is commanded to open, due both to the solenoid opening time, and to the inertia of the compressed air that I am using to drive the engine at this stage of my tests. Any working fluid will have inertia. I recently obtained a digital storage oscilloscope so that I can better see these things, and also measure them more accurately. Unfortunately, the DSO has one faulty channel, and needs repair. This is another reason for being slow with an update on my project. It is instructive (and sobering) to calculate the shaft rotation rate of your proposed engine in degrees per millisecond across the range of speeds that you hope to achieve, and then see how many shaft degrees an opening time of 16 ms and a closing time of 10 ms represents at top speed. For instance, at 900 rpm, the shaft rotation rate is 5.4 degrees per millisecond, and in 10 ms alone the shaft will have rotated 54 degrees. You can allow for the delay time to open, and close, by starting ahead of the shaft angle that you want these events to occur at. The situation becomes difficult though when the total operating time that you need for a given engine speed becomes less that the 26 ms closed to open to closed minimum time of the valves that you are looking at. While I believe that you can speed up the operation of solenoid inlet valves by the techniques that I am using, there is still a practical speed limit, and I think that it is probably somewhere around the 1,000 rpm mark. This is a little frustrating, when you think that fuel injection solenoids, which are, admittedly, much smaller, can work well at much higher speeds than this. Incidentally, I have seen an article from a US firm called Valeo, who claim to have developed electromagnetically operated poppet type valves (their e-valve system). They claim that these could eliminate the need for camshafts in internal combustion engines, and make the valve timing individually controllable for each cylinder. Their website sings its praises, but gives no information on operating times, which might perhaps be the Achilles’ heel of their valve system. I am sure that it takes a lot of power to move poppet type valves at high speed. This is something that can readily be done mechanically, but it becomes a whole lot more difficult when you try to do it fast electrically. This is not to say that you can’t do it, but it is not something that off the shelf electric or hydraulic solenoids readily lend themselves to, except at relatively low engine speeds. On the other hand, it is difficult to change the valve advance angle and opening angle mechanically for different shaft speeds, while it is relatively easy to do electronically with solenoids. I guess that it is just a matter of selecting the type of problem that you prefer to grapple with. Regards Don B |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Mac, after reading the above I come to the conclusion that you don't know either how a 2-cycle internal combustion engine works  .
The inlet ports are totally separate from the outlet ports not the same as you state above. If they were the hot exiting gases would create a nice bang when the fuel/air mixture enters. Actually, most 2-stroke O/B engines use a reed valve and suck in the air/fuel via the crank case. That mixture gets to the top of the piston via transfer ports which direct it in a loop up to the spark plug so as not to take a shortcut out via the exhaust port. What you describe by an "air box" is something I can't imagine - having never seen one or read that description in any 'how it works' article. If its something that only exists in the US perhaps you could direct me to a description of it  , I'm curious now.
Klaus |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Hi Tink It's not so much a matter of knowledge or lack of it rather than being able to communicate what I know. I'm not claiming to be even remotely smart, but I actually am a factory-trained diesel mechanic; albeit that was 50 years ago. I'm also a certified air conditioning and refrigeration tech along with being a licensed plumber, but that's another story. Most of my diesel experience was with Cummins and GM series 671. The Cummins engines I worked on were V-12 and turbo-charged, whereas the GM engines were blown (two-lobed "blower"), but suffice to say the compressor, no matter what type served to cram as much air into the "air box" as we called it, in order to force more than natural aspiration and increase the amount of fuel that could be injected. When an engine "runs away" as in the case where the seals are sucked out of either the blower end bearings or the turbo-charger thrust bearing, raw fuel (or engine oil in this case) dumps into the "air box" and there's no controlling the mixture. Thus, it "runs away" since it has an unlimited fuel supply. It will accelerate until it either runs out of fuel or comes apart. The "air box" is that portion of the block, through which the intake air is forced from either the turbo or blower and in an automobile with a carbeurator, it would be called an "intake manifold". Each engine in my case was a 2-cycle, meaning it fired every time the thing revolved 360* and you're correct that the intake and exhaust ports are separated, but in a uniflow steam engine, that's not the case. In a uniflow steam engine, the steam enters at the top of the cylinder, forces the piston down and exits through the ports at or near BDC (bottom dead center for the rest of the crew). At that point, the piston actually compresses what spent steam remains in the cylinder, but that steam is actually shrinking in volume due to temperature differences (delta T) so it doesn't make much difference. When the piston arrives at or near TDC (top dead center) the injector jams more steam into the cylinder and everything starts all over again. In a diesel 2-stroke engine, the intake air from the "air box" flows into the ports at the bottom of the cylinder and the upwards motion of the piston compresses that volume usually to the tune of about 20:1. When that happens, the compressed air gets really HOT and when the raw fuel is injected, it flashes and away we go! My intention was to draw a parallel between the operation of a 2-cycle engine and a uni-flow steam engine. It's called "uni-flow" because the steam travels in one dirextion only; in at the top and out at the bottom of the cylinder. I was remiss to say "out the same port" but when I said that, my intention was to describe the steam engine and not the fuel-driven 2-cycle. It was a feeble attempt at allegory more or less. I hope this clears things up a bit. 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi again Tim C, Your plan to use a 2 stroke petrol engine in the way that you describe may have a few problems, I think. A 2 stroke petrol engine is essentially a valveless engine, apart from the reed valve or whatever non return system is used between the carburetor and the crank case. The piston controls the admission of pressurized fuel/air/oil to the cylinder, and also the exhaust. As the piston gets part way down its stroke, it opens the exhaust port, then, somewhere near the bottom of its travel, it also opens the intake port. Yes, I believe that you could block off the exhaust and, after removing the reed valve, have the cylinder exhaust via the inlet port and crank case, although the exhaust may not be complete in the relatively short time that the inlet port is exposed. Alternatively, you could also use the exhaust port, or maybe even both, for exhausting. But the problem arises on the piston upstroke after the exhaust port has covered. You will then unavoidably be compressing whatever is left in the cylinder right up to top dead centre. If this is all vapour at this point, then perhaps the only problem will be that the pressure will resist the upstroke of the piston and diminish the amount of power that you develop on the downstroke. Depending on the temperature of the cylinder though, you may finish up at TDC with a significant amount of incompressible liquid in the cylinder, which could stop or significantly damage the engine. This is the problem with using a 2 stroke cycle where every upstroke is a compression stroke, and there is no exhaust valve that can hold open to near TDC as you find in a 4 stroke engine. Maybe there is a practical solution to this (use a solenoid exhaust valve as well??), but it does need to be given some thought. Now that the forum is back on line I can post this, although I note that there have been some other posts come in at the same time Incidentally, Mac is correct with his comments concerning a 2 stroke Diesel engine, however, there are important differences between a 2 stroke petrol and a 2 stroke Diesel engine. A 2 stroke Diesel will still have exhaust valves, and will have an “air box” supplied with pressurized air from a supercharger. The exhaust valves only open for the bottom part of the piston stroke, and the air box pressure helps to blow the exhaust gases out past the exhaust valves. But a small 2 stroke Diesel, even if you could find one, would not help much, as it still has a compression stroke for the major part of each upstroke. Regards Don B |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Tim C Instead of using an existing engine and modifying it, if you want to make a very simple uni-flow engine and you have a lathe, do this: Manufacture a cylinder and crank. Make the piston twice as long as it is wide and make it fit very loosly in the cylinder. Yes, on the surface it appears there will be a lot of blow-by, but in operation, you'll likely have fairly "wet" steam and there won't be as much loss as you might think. I used teflon tape (rolled between my hands to form a string) wound into piston ring lands, but you can get similar results with no tape aned several (like 5) annular piston ring grooves. These are clled "compression" rings; they work like a champ. Make sure it runs very loose. Manufacture a rotary valve on the crank shaft by cutting an annular groove on the shaft, then connect that to a flat spot on the same shaft between the annular grove and the cylinder crank. Drill the shaft alley such that you can attach a tube from the shaft alley to the top of the cylinder. Each time that flat spot cruises past the opening where the tube is, it'll allow steam to flow through the tube, into the cylinder and it will push the piston down. The anular groove by the way is constantly emmersed in steam. The upstroke of the piston will spill off the compression you're worried about. These things run like the wind, very fast. You should be able to build one in an afternoon if you have some round stock suitable for cylinder and piston building kicking around. By the way, you'll have to make a port open to the atmosphere for the exhaust if you close in the crank case. if you're not into building from scratch, use the methods I've outlined and make yours out of a used internal combustion engine. You can even use a 4-stroke lawnmower engine for that matter. Just rip out the valves and cam and you're ready to go, because you're going to remanufacture the valves anyway. Yank out the rings as well; you want the piston to fit very loosly. Not following all this? Send me your email address in a PM and I'll make a drawing or two and send them along. It's really not all that hard to make one of these. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi to all following this thread. My 3 cylinder Briggs and Stratton steam engine project is still progressing at a snail's pace. At this point I believe that I have pushed the limits for the use of solenoid inlet valves as far as I can, using reduced pre-energising and post energising voltages to speed up the solenoid opening and closing times as far as possible. I can get the engine up to 1,000 rpm (on compressed air), but it does not run smoothly at this speed. At 600 to 700 rpm it ticks over beautifully. I have also run into problems with solenoid reliability, as the high speed of operation has permanently compressed some plunger return springs, affected some plunger tip seals, and tends to unscrew the backstops. In one case, it even stripped the thread of the backstop. I guess that it is like the effect of a rattle gun for undoing tight nuts. Many small impacts add up over time. The only thing that I am certain of is that having a means to adjust the inlet advance angle and the cut-off angle is essential to optimise the running of the engine. There is nothing new in this. A Mr Corliss recognised this about 100 years ago, and made some very successful steam engines with this feature. My thinking has now turned to a mechanical rotary inlet valve system that would not have the lag times that solenoids (at least those big enough to act as inlet valves) inherently have. Hopefully, this will let me achieve my goal of 1,600 rpm. With mechanical inlet valves, the only factors then limiting the speed of operation will be the inertia and viscosity of the inlet air or steam. I believe that I have developed a design for a rotary inlet valve that will permit me to readily adjust the advance and cut-off angles, and will have a cross section that is significantly larger than my present twin 5 mm diameter orifice solenoids. The rotary valves will have effective seals, and should have no differential expansion problems operating at 170 C when I do get to the point of using steam instead of compressed air. They should also consume very little power. These valves will sit on a plate that will replace the existing B & S head, and will be driven off the crankshaft via a timing belt, which should give me less bother than a chain. So much for the theory. I now have all of the materials to hand to make them, but need to upgrade my lathe to have a 4 independent jaw chuck, and set up some arrangements to be able to mill some of the parts. There will also need to be some changes to the control electronics, as I plan to use heavy duty (radio control type) servos to change the advance and cut off angles. It will probably take a few months at my pace of working to set this all up, but I will post details if it works successfully. Regards Don B |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Don I would recommend a pressure balanced variable rotary valve, it runs at half engine speed and is simple to make and acts as a point to introduce lube oil as well let me know if you are interested and I will show you how it works. All the best Bob Foolin Around |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Hi Bob, while I have no use for such a valve at the moment I'm curious how it works. Any links to pictures of one? I googled it but found only lengthy patent descriptions without pictures. A picture = 1000 words if one wants to know how something works Klaus |
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