Field vehicle finally takes red fuel (8)
I believe the answer is:
Here is my best explanation:
'fuel' is the definition.
(kerosene is a kind of fuel)
'field vehicle finally takes red' is the subsidiary indication.
'field' becomes 'ken' (one's field of knowledge).
'finally' suggests the final letters.
'takes' means one lot of letters goes inside another.
'red' becomes 'rose'.
The last letter of 'vehicle' is 'e'.
'kene' placed around 'rose' is 'kerosene'.
(Other definitions for kerosene that I've seen before include "No seeker for American fuel oil", "Combustible", "Oil used as fuel in lamps and heaters", "Paraffin oil (E, not I)" and "Sore knee (anag.)".)