I recently saw some of these at a military installation and got to look them over a bit. They claim they can be run on LP, alcohol, gasoline, kerosene, & diesel fuel.
The interesting thing is they are a rebadged Yamaha (the 1kw 2kw, & 5kw) with some external fuel delivery mods. I couldn't find any other differences.
There is a fuel mixture adjustment knob that enriches or leans the fuel ratio and there is an external starting fluid delivery system added (presumably to aid starting on diesel & kerosene).
That is all I could see different. I was a bit surprised they can get a gasoline engine to run on diesel...
Unfortunately I didn't run them so I don't know what they run like on diesel.
I found these intriguing and of great potential from a preparedness aspect.
ETA, now with link:
http://www.inipower.com/products/