Gallery, Projects and General > Mod-Ups!
Pipe and Bolt Engine Mod-Up
shipto:
voted although I do agree yours should have been available to vote for Steve. It would be different if you tried to submit something you did prior to this but as its obvious you followed the same time period as us not a issue. However I will bow to your rule making as it may prevent arguments in the future
vtsteam:
Dwayne, I meant to thank you for your exhaust valve details. The really interesting thing about the long passage for both inlet and exhaust is that it works so well.
I've been thinkng about it a lot. If the pressure pulses travel at lets say the speed of sound (sorry about the units) or 1100 ft/sec, and let's say the tube between valve and piston is a foot, then you'd set up a standing wave at about 550 hz or 550 RPM (that includes time for inlet pulse and release pulse for each revolution).
So the question is, can it exceed that and also run at even harmonics? Is there a "hump" to get over at 1-1/2 wavelength? What is the speed of your engine in RPM? Does it act as if there's a regulator for RPM if the pressure is increased beyond a certain speed --- all kinds of interesting stuff.......
oops, units problems sec vs min, back in a sec (or min.) to edit this!!!!
vtsteam:
Okay, let me start again :)
1100 ft/sec over 2 ft passage travel per revolution would yield about 550 hz x 60 rpm/hz = 33,000 RPM
Okay, I'm pretty sure your engine isn't running up to a wavelength! So, obviously the long passage doesn't seem to pose any restriction (or tuned exhaust style boost) due to harmonics.
It would seem that a separation of valve and cylinder isn't particularly limiting for a steam engine. This is similar to what David Urwick talked about in Model Engineer (quite a ways back) re Stirling engines.
I've been thinking about this in relation to separating the valve and cylinder on uniflow engines -- since they seem to actually require clearance volume anyway. Moving the inlet valve body away from the head down to the crankshaft would allow reduction of mechanical linkages.
The guy who got this right way back at the turn of the previous century was HH Groves. That guy was an unrecognized genius -- he was buildng steam model airplanes with crankshaft mounted rotary disk valves and uniflow exhaust a hundred years ago. It's like Parsons -- everything coming together in one fell swoop.
shipto:
I am ashamed to admit that your talking a bit above my head atm so I will explain the way it goes in my head and maybe you can draw some conclusions from my ramblings.
The engine will work from around 5-10psi up to around 50-60psi at which point the valve leaks to such a degree that the air gets past the O ring and the piston gets a constant pressure, This would probably be solved with a better design of valve but time was pressing.
Anyway discounting the above the air is stopped at the valve until the cam starts to lift at which point the airway open to allow the air through the pipework into the bottom of the piston. The disadvantages of this is that the pipe as well as the bottom of the piston all has to be pressurised before any force is applied to the bottom of the piston. Not only that but the ports in the valve are by necessity small I started with 1mm ports but that was not giving enough of a kick to the flywheel to complete it around to the next valve opening so I then opened it up to 1.5mm which ran but only just, in the end it took 2mm to get it running at the stage it is now. I didnt want to risk going bigger to run it faster as the limited movement of the valve may have caused a problem with it not closing properly. So as you may gather the 2mm hole has to supply air to a 5mm pipe and a 10mm piston a bigger port would of course allow the pressure to build much more quickly and the whole thing would go much faster.
The second disadvantage is that when the cam drops all the pressure is released and so all the air in the pipe is wasted having served no purpose.
Hope this helps.
DMIOM:
--- Quote from: RobWilson on February 15, 2015, 11:26:18 AM ---I disagree Steve (in a friendly way) , just because you thought of it ,it should not disqualify you :med: get your Engine on the list ....
--- End quote ---
--- Quote from: vtsteam on February 15, 2015, 11:45:16 AM ---.......However should you challenge us to, oh say, create a turbine from a tunafish can in one month's time, and put that to a vote, I would not say no to such insolence!......
--- End quote ---
I think Rob's already started (albeit a tin for a large tuna!!)
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