The Frostfire inside The Matryoshka
The Frostfire is an engine specifically made for The Matryoshka.
It is a low-power, silent engine imbued with magic, built from the wreckages of old engines, like the ship.
The parts were later enchanted with ice magic. This keeps it from overheating, lowers the overall temperature of the ship and is quiet.
The engine isn't very powerful, however. It is just enough to power the Matryoshka.