Fuel's particular job, releasing energy (6)
I believe the answer is:
petrol
'fuel's' is the definition.
(petrol is a kind of fuel)
'particular job releasing energy' is the wordplay.
I cannot quite see how this works, but
'particular' could be 'pet' (I've seen this in other clues) and 'pet' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for petrol that I've seen before include "Liquid fuel" , "Common motor fuel" , "Common car fuel" , "The juice" , "Fuel for the internal combustion engine" .)