The most common and most likely answer to this crossword clue is the 8 letter word TURBOFAN
I've seen this crossword clue in Financial Times
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More clues leading to the result TURBOFAN
Buddy explains!

The straight part
We know that "Jet engine" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jet engine = turbofan.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 TURBOFAN mean?
TURBOFAN noun- A turbojet engine having a (typically ducted) fan that forces air directly into the hot exhaust and obtains a portion of the thrust from the turbojet and a portion from the turbojet section.