There are no rules concerning fuel in UW and I think normally it is not needed because we can assume that the ship is refueled every time they reach a spaceport.
However in situations where the PCs are lost (after a failed wild jump roll), on the run from the authorities or are exploring the periphery of the known universe keeping track of fuel can add a sense of urgency like doom clocks in other PbtA games.
This is stolen from the Black Hack’s “usage die” mechanic: You start with a large die size like d20 or d12 and roll every time it is fictionally appropriate e.g. after a jump, trying to escape at full speed etc.
On a 1 or 2 you decrease the die size (d20 > d12 > d10 > d8 > d6 > d4). After the PCs roll a 1 or 2 on the d4 the fuel for the jump drive is depleted. In the games I am currently running that means the ship is still able to traverse a star system (with impulse drive) but can’t jump.
Obviously you could just draw a countdown clock and tick a segment when appropriate but rolling the dice adds a nice element of tension – and in this case gives you an excuse to bring out these beautiful polyhedral dice again.