ahhhhh, propane injection anyone? that was pretty damn cool. and now a short lesson on diesels. the black stuff you see from diesels are called particulates. as you know (or will after i tell you) diesel dont have spark plugs, they are compression ignited. their fuel systems are direct injection and run 10-20x more psi then a normal engine. the way they go through combustion is because the cylinders have so much compression which causes heat and when the fuel is injected the charge ignites itself (the reason for glow plugs to help heat) now since the fuel ignites upon entry, it has little time to mix w/ air and leave an uneven burn with rich pockets, and thats where the particulates come from: a very hot, rich burn. ohh, and diesels cant be leaned out, thats the reason diesels have turbo to put more air in (also the reason they can run propane injection, the diesel form of nitrous). thats why you see the cloud under accel from diesels b/c of the fuel being injected when the pedal is hit with not enough air waiting for turbo spool. but when they hit cruising speed and fully spooled, they are highly efficient.