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Treadmill Dyno
taylorp035:
Last Friday, we clamped the engine to a table and let it run for 73 minutes straight! The previous record was 6 & 1/2 minutes. It was idling at 1100 rpm with a few minutes of goosing the throttle (up to 4k) and low as ~800 rpm. For the last 10 minutes, we upped it to ~2k rpm... it finally got a bit hot on the exhaust end and I think burned the oil off the edge of the seal, which then greatly increased the friction and lead the end of the valve to turn blue (measured at 400F). You could hear the #25 chain start to groan under load, so I shut it off. The head/ block were about 260F, which isn't too bad considering the complete lack of cooling. There were some bubbles in increasing intensity coming around the seal near the end, which leads me to question how well the o-ring held up. I can't wait to tear it apart. Next step is to put it on my friend's go-kart.
--- Quote from: SparWeb on January 15, 2015, 12:46:58 AM ---The pipe is more complicated than I thought. How hard is it to make?
Is it machined as one piece? Can the machining of each path be completed from the port side, or do you have to do some tricky things at the bottom of the hole bored into the bar? Now that I see the way the passages are separated, I wonder if maybe an insert that pushes in from one end would be easier to make.
--- End quote ---
We've made two valves at this point. Both started with precision ground steel, which takes care of the OD. It is machined as once piece, drilled from both ends and then each of the openings in the center get milled on a mill or 4-axis lathe. Generally, you can't mill the transition between the drill operation and the mill operation to be very smooth, so some dremmel work is required. You can make the path better for air flow, but it increases the machining complexity. A nice multi-axis lathe could do a better job... kind of like how custom intake runners are machined in normal engine heads for race cars.
Here is a video of my mini 4-axis mill cutting the valve. The rest was done with a 3/4" drill bit.
https://www.youtube.com/watch?v=qBgn5FxVOYs
--- Quote from: SparWeb on January 15, 2015, 12:48:06 AM ---You have too many files open Taylor.
If I did that on my computer, Inventor would crash!
:)
--- End quote ---
That's nothing. Running CFD, I pushed my laptop to 59 Gb of RAM used (16 Gb actual ram). A solid state disk drive helps in that endeavor. At work, at times I have had 40+ applications open at once (I do a lot of data mining across different programs) and it only has 4 Gb of ram and the motherboard tends to only allow me to use 2.2 Gb of it... the rest of it gets swapped to an encrypted disk drive, which is really slow.
SparWeb:
I fear you'll find a mess where the o-ring once was. Hope the insert isn't too hard to get out.
Maybe a piston ring would work?
taylorp035:
I tore the head apart last night and everything looked just fine. O-rings were good and the sealing surface wasn't too worn or had any major scratches. There was some gooey tar in the combustion chamber and smeared around the valve, so we are going to advance the "cam" timing by a few degrees and see if that helps. On the plus side, any carbon or tar build up helps seal it better. While we had it apart, we machined the spark plug countersink so it's now flat, which should stop some of the leaking. The exhaust was nice and clean, but the intake had some of the tar, so we believe some of the charge is going back into the intake while running.
SparWeb:
Again, I'm impressed! I really didn't think the o-ring would survive.
Have you given any thought to the air exchange process and how complete the burning may be? Air/fuel mix swirling about the chamber - you seem to be equipped to do CFD analysis, so have you done any for this subject? Have you done any exhaust gas analysis? (Maybe you've mentioned it before... this thread is getting really long!)
taylorp035:
https://www.youtube.com/watch?v=8P_YTQQUN3A&feature=youtu.be
Today's run. Now about 2.5 hours of run time total, and approximately 1/4 gallon of gas total.
I haven't hooked an AFR gauge to any of my rotary valve engines yet. I have done some CFD on version 1.0. This afternoon, I just set up version 3.0 in CFD, so I shall see what it looks like, especially with a computer that is 3X faster and 4X more RAM to play with.
Mixing of the fuel and the air should be very good compared to a poppet valve configuration.
Version 1.0 theoretically had a volumetric efficiency of 107% at 3,000 rpm based on my basic simulation. Here is a screen shot from it and a video of some particles from the end view.
https://www.youtube.com/watch?v=uG0dRqNiBQk
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