Increased in range of knowledge applied to energy and fuel (8)
I believe the answer is:
kerosene
'fuel' is the definition.
(kerosene is a kind of fuel)
'increased in range of knowledge applied to energy' is the wordplay.
'increased' becomes 'rose' (I've seen this before).
'in' means one lot of letters goes inside another.
'range of knowledge' becomes 'ken' (I've seen this before).
'applied to' is a charade indicator (letters next to each other).
'energy' becomes 'e' (physics symbol as in E=mc2).
'rose' inserted inside 'ken' is 'kerosen'.
'kerosen'+'e'='KEROSENE'
'and' acts as a link.
(Other definitions for kerosene that I've seen before include "Combustible" , "Oil used as fuel in lamps and heaters" , "Paraffin oil (E, not I)" , "No seeker for American fuel oil" , "Sore knee (anag.)" .)