I am curious about fuels derived from vegetable or animal oils with a flashpoint that would operate a diesel engine. Seems like a good idea to me.

You find lots of articles about biodiesel on the internet, and it's widely used.
It a nice thing to be able to use waste from slaughterhouses, fish industry, food industry as raw material for fuel production.
It's no good in a cold climate, and you can have a peculiar smell from your exhaust!

Check out this link: http://journeytoforever.org/biodiesel_make.html#3choices

Her is everything you need to know to make your own biodiesel!

Don't forget that Biodiesel may get into engine oil with the regeneration of DPF's in new cars. And Biodiesel has a very high boiling point, you will never get rid of it without an oil change.