Due to changes in both factorio Base, and K2, this mod currently needs to have its fuel categories updated for k2.
'vehicle-fuel' is now 'kr-vehicle-fuel'
'fusion-fuel' is now 'kr-fusion-fuel'
'antimatter-fuel' is now 'kr-antimatter-fuel'
It also seems that there isn't a 'nuclear-fuel' fuel type any longer, at least with k2 enabled, so leaving that in the tiers causes a crash.
For my personal use I have updated the "fuel.lua" file accordingly, but this update should also be applied to the mod.
Thank you