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| nearnexus:
I've been building a small flame licker engine to my own design for quite a while (when time permits) and originally used a thin flap valve onto a central hole in the cylinder head to control intake/exhaust. The frictional forces in the linkage were higher than I expected so I've now switched to a side port into the cylinder head (to re-use the original cylinder and piston. The option is to have a sliding shim steel valve held against the side of the head by spring tension OR have a cross sliding rod to interrupt the hole into the head (which should have good sealing properties). The only concern is that the second option will require a much longer port passage into the head. How critical is the length of the inlet/exhaust passage for one of these engines ? I notice everyone seems to go for the shortest possible passage length. I can try the interrupter rod valve first and if no go, mill the head to take a shim steel valve without having to redo the head. Anyone gone down this route ? |
| madjackghengis:
Hi Near, I've been bitten by the "flame sucker bug" for quite some time lately, and I've found their low power means you have to take steps at ever juncture to minimize friction, reduce power consumption and ensure timing is balanced for both lead, on the intake, and allowing the pressure relief on the return stroke, as you still have considerable volume of gases (air,now cool) in the cylinder at the end of the working part of the stroke. I've used the feeler gauge reed valve many times, as it works very well with light enough valve train, I've used a sliding bronze bit about a quarter inch by three eighths, with a groove for a flat spring to clip into, on a half inch bore Phillip Duclos "Flame Sucker", against an aluminum cylinder with bronze piston, and with a brass cylinder and bronze piston, which worked far better, about four or five times the running time before refitting. I've taken what was essentially a scaled up "Poppin" with cast iron cylinder of .750 in bore, 1.25 stroke, stainless steel head, with a ball check valve to release pressure, and set up a sliding graphite valve made out of a generator brush, which works very well, with very reliable action, and not lots of loud annoying sounds as my wife would say. Port length is critical, as the heat of the flame must be radiated into the cylinder, to reduce the temperature and volume of the gases fast enough to keep the engine running effectively. An eighth of an inch of flame position in my latest engine doubles or halves the rpm of the engine. It is using a .005 feeler gauge reed valve with a ball check valve. I will be posting most if not all the build of it tonight or tomorrow, I've been having a flood, and haven't had power for a few days, and havn't had time to get the building of the engine posted. I've been working with long strokes and moderate bores, trying to stay under a two to one ratio, looking to get enough torque to power something. When I've run out of improvements, I will be looking at large bores, and comparatively "square" engines, knowing that will increase the rpm very much, but you have to work out port dimensions relative to bore, more than any other factor, I've found port diameter half the bore diameter works pretty well with the long stroke. I suspect as it gets closer to "square", the port dimension will be more critical and more finicky, but haven't been down that road very far yet. By the way, :worthless: How bout some pictures so we can see? :beer: cheers, mad jack |
| nearnexus:
Hi Mad Jack, Thanks for the detailed response. I knew I would get asked for photo's, but at this time it's all in bits, so not much point. There is a picture at the bottom of my web page on milling that shows my earlier effort before I got the valve linkage in place. http://users.picknowl.com.au/~gloaming_agnet/mill3.html I'm not sure if my idea of using a needle roller for the bottom end is a good idea. It is low low drag, but maybe a ball race would be better ? Anyway for now I will stick with the roller. And here's two more early shots showing the cylinder and crank. http://users.picknowl.com.au/~gloaming_agnet/cq9325rev-a.html I am lengthening the stroke and barrel on this version. The barrel is a bronze liner shrunk into in an aluminum finned section. The finished version nearly ran, but not quite :-) I've decided to go with a sliding feeler gauge, as it won't interfere with the flame as much as a flap and it will self tension if I put a curved load on it. I intend to put a hole in the feeler gauge to mate with the inlet port in the open position. My reasoning is that by doing it that way, the feeler gauge is supported at all times on the perimeter of the port, so fouling of the feeler gauge leading edge is reduced. I also have opened out the transfer port on the inside of the cylinder head to try to get some venturi effect. I'm a bit unsure of the thermo dynamics of the cylinder head. Should the head act as a cooling agent or should it retain some mass to act as a heat element to keep up the temperature of the in comming charge? I only started this project to investigate the thermo dynamics of the vacuum principle first hand - as it is a concept I'm not familiar with. I've seen enough/rebuilt enough internal combustion engines to not want to build my own from scratch ::) This project is like a slow boat to China, but I don't give up easily. Cheers Rob |
| madjackghengis:
Hi Rob, I don't remember who I got plans for the "poppin" from, but the author suggested the port be counter sunk inside, so the incoming flame would not be cooled by passing through the port, and having a "knife edge" for minimal contact area, and in following this advice, I have also used stainless for heads because it's such a poor conductor of heat, and it has made a big difference. The best possible 'ideal' would have the port stay hot, the head part of the cooling, with the cylinder being the vast majority of the cooling, but this would require something like a ceramic port attached to the head, so I've stuck with stainless boat shafting, as it is hard, and wear resistant, and very poor conducting, and in truth, should put a gasket between the head and cylinder, and use stainless bolts, to transfer less heat through them. The port issue changed the way my "oddball flame sucker" ran completely, going from a almost running with a straight port, to running very well, once it was tapered and reduced in diameter to half the bore. I've been trying to catalog some of my findings as I experiment with these engines, and establish some principles to make them easier to get running. Looking forward to watching your's take off, if it almost ran once, it can be made to run :bugeye:, even if by threat and force. :beer:Cheers, mad jack |
| nearnexus:
Hi MadJack, Thanks for the input. I have been playing around with the cam setup for the sliding port valve (feeler gauge) and it's causing me grief as the cam angles to snap the valve open and shut are so aggressive that the roller cam rod binds. Really annoying me. I will have to grind a few brain cells on this one. May have to change from a direct acting cam I think. Having a beer right now while I compute the various options :-) Cheers Rob |
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