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| Flames and flame suckers and eaters |
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| madjackghengis:
With several members busy with flame eaters, I thought I'd take some pictures and delve a bit into how they perform, their nature, and the things which seem to be stumbling blocks. I am hoping this will be considered open for all to post in, I am putting my own thoughts in, but many others have been working on these, and have experience as well. This is intended to be expansive, for all our edification, and not to be my own personal log. So, to start it off, many have asked about flame propagation, and how flames enter the cylinder, I've taken a couple of videos with this focus in mind, and will post them for observation and comment. These were taken of my "oddball" engine, which has an iron cylinder, an iron piston, three quarter inch bore, inch and a half stroke, with a stainless steel head, ball bearings on the rod end, and on the crank shafts with a similar valve arangement to "the poppin'", and an alcohol burner. I have the videos on photo bucket, and have pasted them in the log, but for some reason, you have to click on the picture and be taken to photo bucket to watch them. If someone wants to school me, I'd be happy to learn how to make them appear in the log as actual videos. these videos are with the engine started up cold, with the first one actually being the second one, so it demonstrates a warmed up engine. The flame appears to travel at least an inch through the .375 in port, and perhaps all the way to meet the piston, with the cone of the flame pretty close to filling the port during mid-stroke, and returning to about a .750 ball once the valve closes. It likes to sit slightly to the side, perhaps an eighth of an inch and at ten degrees of angle or so, minimizing blowing out of the flame. It runs a consistent 450 rpm until it is fully warmed up, and then jumps to six hundred, and runs steady there with the current valve reed, which is .009 in thick, and the thickest valve I've used. All the reeds have developed a vacuum formed depression in the reed after a few hours of running, and need cleaning to keep ease of starting due to burnt oil buildup on the reed and the valve face of the head. The engine has probably ten solid hours of run time behind it, so is thoroughly broken in. Comments are invited with enthusiasm. Cheers, Jack |
| Bogstandard:
Jack, Consider this. I had a discussion with Jan Ridders about this proposition and he discounted it straight away, but it is still nagging in the back of my mind. Why do they go faster when reaching a higher temperature, in fact some just won't run until a critical temp is reached? I suggested that it wasn't a cooling effect at all, otherwise they should run from cold, the colder the better. We all know that what happens is that supposedly the air in the cylinder expands with the heat, and supposedly when the air is cooled, the vacuum is formed and so pulls the piston back. The vacuum is actually caused not only by the hot gases cooling, but also an unknown amount of fuel burning in the cylinder and burning away the oxygen that is sucked in with it, as the oxygen is burnt with the fuel, a vacuum is automatically produced. I put it to Jan that the engine relies more on the burning oxygen/fuel principle than the cooling down of the hot gases, so in fact should be termed an internal combustion engine rather than just a vacuum engine. Another point that supports this theory, is where does the pressure come from that can blow out a small flame as the valve opens? There should be no pressure in there, only a vacuum, if anything it should suck the flame into the cylinder rather than blowing it away. Again, my theory is that the imbibed gases are still burning or the gas in the cylinder is stiil hot enough to cause combustion as the valve opens, and the sudden inrush of oxygen causes a sort of secondary burn in the cylinder which then 'pops' out of the inlet hole, then the returning piston starts to suck the flame and unburnt fuel in again. Opinions anyone? Bogs |
| lordedmond:
Well John That certainly puts a different slant on things , in 99% of the time I would concur that the flame is indeed incomplete combustion , in that case it would continue to burn ( in a older car petrol engine there is enough petrol in the exhaust to burn) , maybe that why the crud builds up inside the cylinder. so if this is the case we do need some air to get in not a total flame covering the port ? Stuart |
| cfellows:
If there is continued combustion in the cylinder, why wouldn,t there be continued net expansion as occurs in an internal combustion engine? I would maintain that if the engine speeds up, it's probably just because things are looser and move more freely. Regarding the exhaust gas question, I would think this is just the residual gas that was sucked in. At some point during the return stroke the pressure equalizes then exceeds outside pressure as the swept volume continues to decrease. Chuck |
| John Hill:
--- Quote from: bogstandard on March 24, 2011, 12:52:55 PM --- Another point that supports this theory, is where does the pressure come from that can blow out a small flame as the valve opens? There should be no pressure in there, only a vacuum, if anything it should suck the flame into the cylinder rather than blowing it away. --- End quote --- John, my understanding is that the hot gas in the cylinder cools and reduces in volume creating a lower pressure and atmospheric pressure then pushs the piston in. If the valve did not open at all (extreme case for demonstration purposes only) the flywheel would carry the piston past the point of equal pressures and so create a high pressure in the cyclinder. I suggest that if the flame gets blown out in that way it may be a case for opening the valve earlier. John |
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