Diesel fuel has a very long shelf life on its own. Add stabil to it and it can last indefinitely. We buy it in bulk and that lasts us 2-3 years on the farm. Now gas on the other hand, not so much
Suppose it depends on what its burning in.
I'm sure with a little experimneting most systems can be made to run on junk. Look at the number of trucks people set up to burn leftover grease from McDs and Chinese restraunts.