Light fuel, heading off (6)
I believe the answer is:
ignite
'light' is the definition.
(I've seen this before)
'fuel heading off' is the wordplay.
'fuel' becomes 'lignite' (type of coal).
'heading off' means to remove the first letter.
'lignite' with its initial letter removed is 'IGNITE'.
(Other definitions for ignite that I've seen before include "Swan constellation" , "Catch fire; provoke" , "Set fire to, light up" , "Cause to catch fire" , "Cause to start burning" .)