It's a Running Story

It has been a week of continuous reading and experimenting on my little flame eater engine, since last Sunday's post about it not quite running.



A brief overview of things up to now.  I started out by researching how to make it sound like a "known good" engine sounds.  It didn't sound right and that seems to be caused by the piston itself.  I started coming to the conclusion my piston was too small and I wasn't getting enough compression.

Early in the week, I read comments to one of the many flame eater videos on YouTube.  One commenter said these engines either run hot or cold.  If they're running cold, they quickly warm up enough that the expansion of the cylinder due to the heat of the slurped up flame causes the cylinder to get too big to keep the compression.   If they're setup to run warm, they'll be so tight at room temperature that they just won't turn over.

That gave me the idea to get the cylinder cold, with  the idea that it would shrink up more than the graphite and give me better compression.   This would test the idea that the piston is too small.  It actually ran!  It got to running 10 seconds and I started fumbling with my phone to grab a video of it, whereupon it stopped running.

Now I decided to turn a new piston to be a tighter fit in the cylinder.  The first attempt at a new piston didn't work; I overshot the diameter I wanted.  This piston is the third one I've made for this engine.  All three have been graphite, but that's a suggestion from the forums.  The original book plans say cold rolled steel (CRS), bronze or cast iron.  I originally bought a bar of  CRS to turn the piston out of before going for the graphite.  Now I'm considering making a fourth piston, this time out of CRS.

A commenter on the forums tells me that the behavior I'm seeing is pretty common and it might really be OK now.  He says that if it's starting cold, the engine stops because as water from the combustion condenses inside the cylinder, and increases drag.  He says that once the temperature of the engine reaches its running temp, in 2-3 min, it will run indefinitely.

I will experiment more with that before I decide to make another piston.