That Lohmann motor is pretty interesting. It looks like it has a decomp valve in the head, and three piston rings. Not sure but it might be an acme thread to move the the head in and out, which would make sense. Acme threads are used on vices or other applications where you need a lot of force.
Lol those model airplane engines run on poppers:
"These 'diesels' run on a mixture of kerosene, ethanol, ether, castor oil or vegetable oil, and cetane or amyl nitrite booster."