I am reading this thread with great interest.

The diesel idea is a great one and I experimented with a Davis ST 45 and a PAW .033 years ago. The exhaust note was great and running lamp oil made it very clean. The thing I didn't like was the magic ways of trying to keep the ether in the fuel and the potential cost to run a large 1.60 cu in engine. Otherwise diesel would be for me.

The idea of running a Diesel without ether makes it sound much more user friendly and less expensive.

It would be cool to try a Turbo plug equipped contra piston on a large diesel conversion to see if you could light it off with external heat and not have to chase settings. I don't know how you would energize the plug and move the contrapiston. Maybe the plug could be set toward the outer edge of the combustion chamber if the engine was big enough.

The other way would be to make the compression adjustment like on a Enya four stroke diesel (move the rear bearing to increase or decrease head clearance) and use a glow plug to get things going.