Ingenious fuel, replacing source of power with nitrogen (4)
I believe the answer is:
neat
'ingenious' is the definition.
(thesaurus)
'power with nitrogen' is the wordplay.
'power' becomes 'eat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'with' means one lot of letters go next to another.
'nitrogen' becomes 'n' ('N' can be a synonym of 'nitrogen').
'eat' after 'n' is 'NEAT'.
'fuel replacing source of' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
(Other definitions for neat that I've seen before include "Drink with no water added" , "Excellent American" , "Steer - straight - trim" , "Tidy and dapper" , "straight to the barmaid" .)