Change the name of fuel (7)
I believe the answer is:
methane
'fuel' is the definition.
(thesaurus)
'change the name' is the wordplay.
'change' indicates anagramming the letters.
'the'+'name'='thename'
'thename' with letters rearranged gives 'METHANE'.
'of' acts as a link.
(Other definitions for methane that I've seen before include "Marsh-gas" , "Get fuel" , "Marsh gas - the name (anag)" , "Main constituent of natural gas" , "Main component of natural gas" .)