The most common and most likely answer to this crossword clue is the 4 letter word FEED
I've seen this crossword clue in The Daily Telegraph
F
E
E
D
More clues leading to the result FEED
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 = feed.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 FEED mean?
FEED noun- Food given to (especially herbivorous) animals.
- Something supplied continuously.
- The part of a machine that supplies the material to be operated upon.
- The forward motion of the material fed into a machine.
- A meal.
- A gathering to eat, especially in quantity.
- Encapsulated online content, such as news or a blog, that can be subscribed to.
- (ditransitive) To give (someone or something) food to eat.
- To eat (usually of animals).
- To give (someone or something) to (someone or something else) as food.
- To give to a machine to be processed.
- To satisfy, gratify, or minister to (a sense, taste, desire, etc.).
- To supply with something.
- To graze; to cause to be cropped by feeding, as herbage by cattle.
- To pass to.
- (of a phonological rule) To create the environment where another phonological rule can apply; to be applied before another rule.
- (of a syntactic rule) To create the syntactic environment in which another syntactic rule is applied; to be applied before another syntactic rule.
- To reward for services performed, or to be performed; to recompense; to hire or keep in hire; hence, to bribe.