Matheus,

Yes, your thinking was the same as mine and I did try several other volatiles and they did NOT work well. It appears that SOME ether is required, at least if you want to have good throttling. If not, then any diesel engine can be made to run without ether. Starting is the problem and that is solved either by applying heat directly to the engine with a heat gun, or using a high ether prime to get a few prime runs that warm up the engine sufficiently. At the field, careful application of a small torch would work.