Litre in fuel knocked over — it gets blown up (4)
I believe the answer is:
lilo
'it gets blown up' is the definition.
(I know that lilos get inflated)
'litre in fuel knocked over' is the wordplay.
'litre' becomes 'L' (abbreviation).
'in' is an insertion indicator.
'fuel' becomes 'oil' (oil is a type of fuel).
'knocked over' says the letters should be written backwards.
'l' going into 'oil' is 'olil'.
'olil' reversed gives 'LILO'.
(Other definitions for lilo that I've seen before include "Blow-up mattress" , "Inflatable mattress" , "Bathing-beach" .)