Actual mechanics for fire fuel?

So a while back I picked up a habit of using random small bits of zombie clothing to fuel my fires. Recently that doesn’t seem to work as well as it used to, apparently due to the new fire mechanics.

Can anyone explain how the actual mechanics of that works now? And maybe how to look up the ‘fuel value’ of various items?

What makes you say there is a new fire mechanics?

Wait there are fire mechanics?

Yes, fires are spreading using some rules.

I know that but for fire duration

What do you mean? Fires are not static.