Gallery, Projects and General > Neat Stuff
Strange but simple engine.
vtsteam:
John was once interested in a flame licker engine that had internal combustion -- this is pretty close to that, I think. The main difference is that there is spark ignition instead of a pilot flame. I think ignition on this one may occur as the methanol is being taken in, before the intake valve is fully shut. Depending on the timing, there could be a vacuum going on while the valve is closed after BDC. And maybe time for expansion before BDC. The long thin brass tube cylinder does have a lot of cooling area.....not sure......
RussellT:
The extra ports might well help with avoiding mixing of the intake and exhaust, I had assumed that the large cylinder volume compared to the "carburettor" would take care of that but the induction stroke is short compared to the length of the cylinder.
It sparks as the ports close (15 deg ATDC?) and then the burning mixture expands for the power stroke, the valve opens again around BDC (165 deg ATDC or 15 deg BBDC?) to allow the exhaust gases to vent before BDC to prevent the engine having to compress them - if they continue to expand they'll be exhausted and then the piston pushes out the rest until TDC and then sucks in mixture until the ports close and the cycle repeats. If that's right then there is a very short time for induction but it fits as the valve timing has to be symmetrical between BDC and TDC.
I wondered about whether there was any vacuum effect because it is described as an atmospheric engine (see, I can read German :lol:) but I can't see how there could be.
Russell
shipto:
--- Quote from: shipto on February 26, 2015, 05:13:16 PM ---bdc to approx 15 degrees
--- End quote ---
just realised I got this upside down its should be tdc not bdc.
vtsteam:
--- Quote from: RussellT on February 28, 2015, 04:07:48 AM ---The extra ports might well help with avoiding mixing of the intake and exhaust, I had assumed that the large cylinder volume compared to the "carburettor" would take care of that but the induction stroke is short compared to the length of the cylinder.
It sparks as the ports close (15 deg ATDC?) and then the burning mixture expands for the power stroke, the valve opens again around BDC (165 deg ATDC or 15 deg BBDC?)..............snip.........but it fits as the valve timing has to be symmetrical between BDC and TDC.
I wondered about whether there was any vacuum effect because it is described as an atmospheric engine (see, I can read German :lol:) but I can't see how there could be.
--- End quote ---
I'm thinking the valve timing is symetrical but that would mean just a short interval either side of TDC for both exhaust and intake. And that would support the atmospheric concept as there would be plenty of time to develop power from the vacuum.
There may be some energy from the power side, too, but methanol burn is pretty instantaneous compared to the RPM of this particular engne, and the port is open at ignition -- or so it looks. I think it's sort of an inefficient combination of IC and atmospheric engine -- as named. A quick way to find out what was happening and how much contribution each part of the stroke provides would be to insulate the cylinder and check the RPM compared to normal.
RussellT:
--- Quote from: vtsteam on February 28, 2015, 10:38:40 AM ---I'm thinking the valve timing is symetrical but that would mean just a short interval either side of TDC for both exhaust and intake.
--- End quote ---
I don't think I explained the symmetry very well. I think the valve closes 15 deg after TDC and opens again 165 deg after TDC remaining open after BDC until TDC (open for 210 deg total).
The valve opening is symmetrical around the halfway point between TDC and BDC - the halfway point is the extreme end of the cylinder oscillation. That's exactly the same as my mod up engine but I used two ports.
Russell
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