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Take two OHC engines (boxer engines would be simpler). Rip off the heads. Cut holes in some old tiles and use as a new shared head gasket. Leave the cooling system on one intact and pipe in hot water from your solar collector into the other using the existing water pump.
The only real work to do is
bodging the timing chain/belt to be sufficient to lock the phase of the two engines.
Serve energy from alternators.
Stirling
http://en.wikipedia.org/wiki/Stirling
I'm not so sure that the residents merit such harsh treatment. [Jinbish, Mar 24 2009]
[link]
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Darn. At first glance I thought it said "Scalp Stirling". I wondered how you were going to pull that off. |
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Not a plan to switch us over to the Euro, then. Phew. |
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what do old tiles have as special abilities, that helps them being a gasket? |
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WcW, impractical for some reason ? Care to ellucidate ? |
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//old tiles// I dunno, something that has reasonable insulating properties and is not too pliant. |
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This simply wont cause the engine to turn. What forces do you think will come into play to turn the crank? Just heating all the cylinders evenly is not going to make the engine act as a pump |
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//Water will seep past the rings and destroy the engine.// Cooling circuits left intact. One runs as was and the other circulates heat (ok, problem with some head designs maybe). |
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//What forces do you think will come into play to turn the crank?// Damnit! Now what fiendish device could we possibly use for that with recycling in mind. [edit: in case you misunderstood, only one engine is heated] |
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So this is an Alpha Stirling Engine, in an opposed piston configuration? |
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I think it might work, provided you don't lose too much energy through friction, etc.. |
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//So this is an Alpha Stirling Engine, in an opposed piston configuration// |
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I'm dying for somebody who is more of a grease monkey to try this. Max 1 day's work ? |
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On second thought, you don't have any room to stick a regenerator between the heating and cooling cylinders... so the engine won't be efficient. |
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//so the engine won't be efficient// |
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Not too worried about that since its from scrap. 20% from scrap is better than 60% from an all new engine. For the solar collector I'm thinking old double glazed windows (condensed up) circulating used filtered engine oil or just water. |
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I'm not saying it's a bad idea, just that you could make the engine more efficient by adding a regenerator. |
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I would suggest the following: |
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Instead of connecting the two original engines head-to-head, mount the two engines side by side. If you do it right, you'll be able to adjust the positions of the engines in such a way that the timing chain/belt snugly connects the two engines' shafts. |
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Leave the engines' heads mostly intact; remove the valves, seal off one of the two ports in each head, and attach a piece of metal tubing to the open port. |
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Use tubing to connect corresponding pairs of pistons in the two engines, but have the tubing pass through a regenerator in between. A cheap regenerator can be made by stuffing a piece of pipe with steel wool. |
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I'd also suggest that since both engines are mechanically linked, it would be simpler (and just as powerful/efficient) to only take electrical energy from one of the two alternators. |
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//seal off one of the two ports in each head// |
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Good idea, and I like the side-by-side (saves having to be careful about the oil pumps) but the manifolds funnel into a single pipe. Maybe the regenerator could be worked into a thicker device instead of the tiles ? |
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Look lets say that you do pipe one bank of cylinders to the other and you "heat one side", and not the other (you need to cool that side), will it be enough to overcome the friction of the engine or will the pressure simply slowly leak past the piston rings ? (yes) The problem is a lack of seals and the ample friction as well as the simple lack of temperature differential between the hot and cold sides. |
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//will the pressure simply slowly leak past the piston rings// |
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The rpm will be comparable with tickover or maybe better so maintaining compression shouldn't be a problem. |
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Cooling the cool engine won't require much more than standard radiator/fan cooling since we're not demanding the kind of energy that accelerates a car from 0-60 in 10 seconds. |
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Friction losses are the only worrying factor, but given that a solar collector could well pump in quite a few kilowatts that stacks up nicely against an engine running on idle. Consider: how long an engine takes to warm up running on idle versus piping in hot water (thermodynamic argument). |
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// Max 1 day's work ?// I'm busy. |
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look. If you really want try this here is what you need to do: |
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1) get a used VW shortblock ( typ3 or tpy4, not siamese port) |
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4) drop intake valves and seal valve guides |
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5) X pipe the intake pipes so piston motions are paired (1x3 2x4) and engine is sealed to self, replace intake plenum with two "regenerators" (design?) |
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6) Plumb a small wood stove chimney pipe to flow across one bank, cold air to flow across the other |
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7) Give the engine a spinning start |
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Got it to work yet WcW ? It would seem a natural progression after //no// and //This might work//. |
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Seriously though, I think this is one of my all time best ideas. It would however be a non idea if various car companies hadn't scrapped stirling engine cars in the firstplace. Imagine; any scrap car could be turned into a solar generator, from polluter to green energy. Damn them! Damn them all to hell! |
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you need a large volume of waste heat at a high differential temperature. Also you need an engine that is minimally insulated and will communicate a minimal amount of heat from side to side. The boxer four subaru or vw engine could work in a similar way but i suspect that the conductivity of the heads would be too low. A finned aluminum head sealed and submerged in the liquid medium would be best. |
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WcW, I'm pretty sure you are still overlooking the idea's suggestion of *two* scrap engines. These can be easily thermally isolated e.g. by the use of a homemade regenerator, old tiles etc. |
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I suggested boxer engines (wasting half the cylinders) because these could be mated without turning the engines into an orientation they are not used to. |
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The communication of heat (from engine to engine) is the Stirling process. |
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This just leaves head conductivity. Again this does not seem to be a problem as engines are designed to get rid of lots of waste heat, in fact probably more than you'd want to pump in so thermal conductivity to the cylinders is again a non-issue. |
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The liquid medium you suggest in my configuration uses nothing more than the existing water pump to heat the head from solar collectors which raise the temperature of water (or oil). So water cooled engines are pretty much a requirement. |
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Let's recap. An old engine with a 50% efficiency gets rid of the remainder of energy using the water cooling system. Assuming a hot water source, use the same system to heat the cylinders. Since heat valves virtually don't exist, I'd say the process is reversible giving you plenty of differential to the cold engine which is as before is busy trying to get rid of heat using the existing pump, radiator and fan. |
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The thermodynamic argument remains, if you have a hot water source that can heat the water equal or greater to tick-over temperature then friction will be overcome. |
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[UnaBubba] would have some issues with this, i think... |
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oh, even worse. Well TWO engines means we need twice as much plumbing and we face twice as much friction. Remember that the two engines need to be locked together by way of the crank and the pistons have to be X mated to act in tandem (the net movement of the pistons in most engines means that the volume of air in the cylinders is uniform thus cannot be treated as one cylinder of a two phase pump, you did realize this, right?) |
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//The only real work to do is bodging the timing chain/belt to be sufficient to lock the phase of the two engines.// |
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nope, you don't want or need the valve motion anymore, toss the camshafts and their high friction. What you need to do is focus on having only one engine, with one crank and lube system, and a crank operated fan for the cold side. |
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//nope, you don't want or need the valve motion anymore, toss the camshafts and their high friction// |
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Doesn't surprise me that you didn't read the rest of the idea if you didn't make it to the second word. |
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you need the heads because they complete the coolant loop. without the heads, on most engines, the coolant will not flow. In addition the bulk of the coolant surface is in the head. Without the heads your idea of using a water cooled engine looks even weaker. Guess I didn't include that in why I thought your idea wouldn't work. Also you should note that on many engines the piston tops rise higher than the deck of the block. |
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//you need the heads because they complete the coolant loop//
- //Cooling circuits left intact. One runs as was and the other circulates heat (ok, problem with some head designs maybe).// |
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//Also you should note that on many engines the piston tops rise higher than the deck of the block.
//
//Cut holes in some old tiles// and the regenerator discussion. |
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Ok, I think I've finally got my head round this. |
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First, an i4 engine has cylinders that are 180 degrees out of phase. An alpha Stirling needs cylinders that are 90 deg, so you either need to modify the crank of 1 engine or use 2 engines. |
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Secondly, you are interested in pairs of cylinders so you can have 2 pairs in 1 engine or 4 pairs in 2 engines, I don't see why there would ever be wasted cylinders. |
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The heat exchanger can be fairly simple, just butcher a radiator and use it for all the pipes. That would make it more effective as cylinders heat/cool eachother between phases. |
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I think the biggest problem is going to be transferring heat into the cylinder. in a 2-engine design, I think the best way would be to keep the head and heat it. However you do it, you'd need to insulate the whole block so it doesn't cool from ambient air. |
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In the 2-engine design, won't the cold engine automatically time to 90deg out from the hot engine without them being geared? |
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//in a 2-engine design, I think the best way would be to keep the head and heat it// |
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I'm coming round to that. Seems there's going to be some fabrication any way you do it and its probably easier to remove the exhaust valves and connect a few pipes than re-enginer the cooling circuit. |
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//won't the cold engine automatically time to 90deg out from the hot engine without them being geared?// |
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Interesting idea. I'm guessing not, but potentially the starter teeth on the flywheel could be mated with an additional cog, like er, the spare cog from the second starter ! |
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keep the idea simple. since we all know that the Stirling concept works what you are trying to demonstrate is that it can be mocked up from scrap, any two pistons on a common crank 180* out of phase (relative) will function so long as the other fundamentals are good. I think you need to focus on how you are going to get one bank hot while cooling the other bank. Also some attention to absolutely minimizing any friction and pressure leakage. Oiling and a oil pump might be nice in the long term but for testing I would remove it and grease everything, same goes for the other engine accessories, even the flywheel, K.I.S.S everything. As for the water cooling thing, I think that you could split the cooling on an older subaru ea1600 or ea1800 engine with relative ease, then plumb cold water through one side and your hot water through the other. For simple experiment I favor the VW aircooled but that is out of pragmatism since I suspect you will need more temperature differential then is going to be easily achieved. |
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//I think you need to focus on how you are going to get one bank hot while cooling the other bank// |
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Please focus. Two engines, that's 2, one cold engine plus one hot engine equals two engines. Both have water circuits. One left alone to cool using the radiator the other drawing hot water from your solar array. Its still in the idea way way way up there. |
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//what you are trying to demonstrate is that it can be mocked up from scrap// |
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What I'm trying to do is come to a design that actually generates power, uses common scrap and is not overly specialised, even the boxer engine requirement I see as too specialised. |
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Is there any reason that some i4 engines are more suitable than others? I would assume the older the better, but other than that? |
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Have you considered using a single V8 engine? I would have thought you'd have bigger simpler engine options. |
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BTW, my radiator cracked the other day, overheating the car, so I sat pondering a number of Stirling ideas. |
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//Have you considered using a single V8 engine?// |
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A single block is not a good solution as the block is the thing that heats and cools the air via the cylinder walls. So you need one hot block and one cold block for a Stirling. |
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True, but I was thinking more of the fact that it has 2 heads and that most of the block is seperate (varies for each engine). I just thought the simplicity would be worth the inefficiency. |
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On the hot side, having the block cool the cylinder as it reaches the end of the 'power' stroke is an advantage, it's only on the cold side that you have a problem where it's being heated at the end of the 'intake' stroke. |
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I don't see the problem there as each block remains at a fairly constant temperature and heating or cooling starts as the air is drawn in by the piston. |
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I think I've found a problem. The gas volume needs to go from 1/2 cylinder volume to 3/2 cylinders so it would have a 3:1 expansion, which means a 3:1 temperature difference (around 900K:300K or 628C:28C) and even that assumes 100% heat transfer efficiency. |
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If we assume that the regenerator has 1/2 a cylinder's volume, the ratio drops to 2:1 which is much more doable. Increasing the regenerator volume any further just reduces efficiency and makes a temperature gradient even harder. |
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Basically, you need to make it very hot, and that will mean finding some specialised oil for the cooling/heating system like jet turbine oil, which kinda defeats the easy to make from scrap aspect. |
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Also, the working gas would need to be under pressure to have a decent amount of heat transfer and torque, I should think at least 10bar(150psi). There would probably be some leakage so you'd have to add a compressor to the circuit. A small car tyre compressor might do it, but it would have to be one of the better ones, that go up to that pressure. |
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Efficiency isn't a big priority here, its just whether it works with little fabrication. That rules out a pressurised working gas as piston ring seals aren't perfect and the pressures will soon equalise to center on atmospheric pressure. |
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I guess I should put the effort in to run the numbers and see whether the compression ratio can at least overcome friction. |
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I couldn't find any actual figures for engine friction. Anyway, it would be different once you remove the valves and the compression stroke, I guess you'd have to turn one with a torque wrench. |
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I also don't really know how to crunch the numbers, but I'll go as far as I can:
Assume 500cc cylinders measuring 8cm diameter by 10cm stroke and 30C temp increase.
Pressure increase = 0.1atm = 0.1kg/cm^2 x 50cm^2 = 5kg = 50N |
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The problem with this calculation is that the calculated force only occurs when the piston is stationary at the point of lowest volume, once the volume increases, the pressure decreases unless the temperature continues to increase. |
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Therefore, at the end of the stroke, when the piston doubles the cylinder volume, a temperature increase of 300C is needed just to keep the pressure the same at 1atm. |
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I suppose you would need to be somewhat familiar with the actual interior of an engine in a hands on kind of way. |
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