Okay, I have a quick update on my Leitinger style nozzle. Granted, it has only had maybe an hour of run time- but so far it is looking pretty good.
It uses a much smaller orifice - 11/32" (8.7mm), and is currently running a little 204cc Tecumseh engine at like 3600 rpm. I couldnt get a really good view of the nozzle, but it felt like the edge of the hole was still sharp. I can shoot an IR thermometer inside when its running, and I have never gotten a reading of more than 800F, and 600-750 is more typical. None of the metal visible inside is glowing, there is just a brilliant little spotlight of yellow light shining down from the hole. I think the total mass of the nozzle is about 7 lbs.
I am not using any EGR or water at the moment, but I am probably going to add exhaust back in to boost the fuel efficiency.
It seems to be forming a little slag volcano on each run, which I can push out of the way with a welding rod to start it up again.
I found no ash when i cleaned it out, but it did seem like the charcoal was pretty dusty.
So far, this seems like it shows promise - I will post more info once I have some more hours on it.