Space clam has most of it. Diesel is a mix of kerosine,oil and I believe ether or something similar. A glow engine (which looks like an RC diesel BTW) uses methanol and a chemical reaction with platinum in the glow plug to ignite the fuel.

Diesel however use heat from compressing the fuel air mixture in the cylinder. Diesel RC engines have a screw in the center of the head rather than a glow plug. This is the compression release (I think that's what they call it). You use this to move a button inside the engines cylinder to raise and lower the compression. You back off the compression to start it. Then screw the button in to increase the compression to normal operating levels.

Diesels have tons of torque. They can swing a much larger prop than an equivelant glow engine. They are supposed to be quieter ( Just what I have heard) and also are supposedly more fuel efficient. There are companies out there, i believe Davis Diesel is one, that sells conversion heads for popular 2 stroke engines. Diesels stink and make quite a mess I am told.

I hope this helps. I am not a diesel expert. I hope someone else can chime in here.

Mark Shuman