“What is a deuterium-antimatter reaction regulated by a dilithium matrix — or in the case of Romulans, a quantum singularity; or quantum slipstream which utilizes benamite crystals, though whether it is a fuel source is ambiguous and the subject of much speculation…?”
https://old.reddit.com/r/MawInstallation/comments/hzou7z/the_death_stars_engines_are_ridiculous/
According to this geek, they were flying past the 123 main thrusters while flying down the trench in the first movie.
Also they provide a ridiculous amount of thrust.