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| Stilldrillin:
--- Quote from: sbwhart on December 10, 2014, 01:49:00 AM ---"O WOW" indeed :clap: Its getting there Dave :thumbup: Stew --- End quote --- Thanks Stew! :beer: Considering, it was only loosely lashed together. I was very surprised, how it took off! :bugeye: I had three runs, as shown. Each time, (I guess), the condensation slowed, and stopped it. Will first, heat up with hot air gun, or fill with hot water, in future. :thumbup: It's all a learning curve........ :scratch: David D |
| vtsteam:
My take on vacuum engines: There's two things happening that make for condensation: one, the cylinder walls are below the boiling point of water. And two: combustion of conventional fuels produces C02 and water. So that water necessarily gets into the engine when the flame burns inside the cylinder. Power in a vacuum engine occurs because those gasses are cooled by the cylinder walls and the gas contracts. So one way of increasing power is to cool the heated combustion products more quickly -- in other words a colder cylinder. But the problem is if the cylinder wall is cooled below the boiling point of water, you get condensation on the cylinder wall, and that acts like a brake. Particularly if the clearance is close, and if there are no rings or grooves in the piston where the moisture can go to clear the bore. So I'm wondering if grooved pistons would help reduce friction when there is a lot of cooling and a close fitting piston. The other way of increasing performance is to introduce a hotter gas, and let the cylinder run hotter than the boiling point of water. In that case there should be no condensation, once an engine warms up, and it should run freely. This would require a hot flame, high flame volume, and a lower efficiency cylinder cooler. The cylinder should be as cool as possible, while still somewhat above the boiling point of water. A much higher temperature than that is unnecessary and would just reduce power. Anyway, just some ideas.... |
| Stilldrillin:
Thanks for your thoughts, Steve. I like the idea of piston grooves, to hold the initial condensation....... :thumbup: The shop temp was only some 8*, if that. And it was only a quick proving run. The cylinder and piston need to be nearer the 100* mark, at the start of future tests. Next job, is the graphite piston. When the weather is a bit kinder to me old joints....... David D |
| vtsteam:
David, I thought of grooves only because I thought I remembered the oil scraper ring in an IC engine doing sort of the same thing. I can't remember whether they might even drill through some IC pistons at the groove to clear oil :scratch: |
| Stilldrillin:
A piece of s/s, 2mm x 75mm square, (£2. Ebay), was made into a piece of 55mm dia. round. Drilled, to match the cyl head........ Recessed, 25thou deep, for shutter blade........ Window, cut out........ Piston's eye view. The top of the blade can bend outward, to relieve any unwanted pressure........ I assembled, loosely, no oil. Still with the c/i, (now undersize), polished piston. Had a bit of a surprise, during engine warm up. It runs, on the hot air gun! :bugeye: Official trial video........ I think the next job, aught to be the twin wick burner. Thanks for looking in! David D |
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