EEC's changes applied to fossil fuel blend (8)
I believe the answer is:
coalesce
'blend' is the definition.
(I've seen this before)
'eec's changes applied to fossil fuel' is the wordplay.
'changes' indicates anagramming the letters.
'applied to' says to put letters next to each other.
'fossil fuel' becomes 'coal' (coal is a kind of fossil fuel).
'eecs' is an anagram of 'esce'.
'esce' after 'coal' is 'COALESCE'.
(Other definitions for coalesce that I've seen before include "To bring together" , "Make one whole" , "Come together in one mass" , "Grow together, amalgamate" , "Unite" .)