ORIGINAL: pe reivers
I would hardly call jet fuel ''heavy fuel''
In ships engines the normal viscosity heavy fuel is black crudlike thick syrup, and needs heating to be pumped. Car diesels also use heavier fuel than jet engines. Car diesel fuel still rates as light fuel.
Bio diesel mostly is car diesel fuel where the heavier bio oils are mixed in with about 10% - 40%
That black crudlike stuff is "Residual Fuel." The price makes it attractive to large, slow speed diesel operators, but there is a caveat. You cannot let the engine cool off with Residual in the injectors (assuming you want the engine to start again.)
The engine is fired up on distillate (diesel fuel) and run until hot, and the residual is heated to high temperature with pressurized steam heat exchangers. When the residual will flow, it is switched into the supply and the more expensive distillate is switched off. Before shutdown, the distillate is switched into the supply, and the residual is shut off. After a suitable amount of "flush" time, the engine can be shut down without sticking the injectors.
Residual, if I remember correctily, is what's left after everything profitable is distilled out of the crude oil. One colleague called it the "Tailings". Heavy? You bet!
Now why did I bring that up.....??? Oh, right. Just FYI.
Dave Olson