The most common and most likely answer to this crossword clue is the 6 letter word BENZOL
B
E
N
Z
O
L
Buddy explains!
The straight part
We know that "Fuel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fuel = benzol.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BENZOL mean?
BENZOL noun- An aromatic hydrocarbon of formula C6H6 whose structure consists of a ring of alternate single and double bonds.
- (in combination) Sometimes used in place of the phenyl group.
- An impure benzene (mixed with toluene etc), used in the arts as a solvent, and for various other purposes.
- Benzyl alcohol