Stewart,
you are confirming that commercial diesels cannot regularly run on triglycerides , straight or waste they are, unless in particular conditions or additional apparatus or running methods are used.
When glycerin is properly stripped out of oils, the resulting product can run on commercial diesels, but is so different from oil that I suggest you not to fry anything with it.
I am warmly suggesting to fry chips or fish with olive oil (better fish than chips), you will lubricate better your engine.....for free. Tomorrow friday maybe, as is usual here to eat fish, I will make this absolutely new superecological lubrificant using the same brand of oil of my last test . After proper measurements it will run on the Mars benchmark, maybe it should be better to find a marine version for this test!
Ugo