I would go with a Cox .049 (0.8cc) engine set up for diesel or compression ignition use with the special head and crankshaft myself too. Also maybe the RC carb on it as well. The carb lets the microcontroller circuit control the engine based on the current load from what is drawing power from it. It was basically an electronic governor on the engine of course.
http://coxengines.ca/product.php?pro...=39&page=1
Using a Cox engine would make getting parts for it easier for things that wear out over time.

A number of years ago I built a small generator charger for a robot that used a Enya .25 RC diesel engine, it worked pretty good at the time. Alas it was a project done for someone else so there are no pics of it or anything.


You might want to get a Heat sink or make a heat sink to help cool the engine better. I would also fabricate a fan of some sort to move air across the engine too.