The Dieselkraftwerk is one of Wolfenstein: Youngblood's more eclectic weapons, its use inevitably resulting in loud explosions and showers of Nazi giblets. However, finding it can't be done from the start of the game.
In order to get to the Dieselkraftwerk's location, you'll have to advance into Political Detention Area 4. Once there, set Raid Mission: Brother 2 as your active, although you'll want to be at least level 20 and have an upgraded stealth cloak before tackling it.
As you follow the waypoint, you'll soon find that the entrance to the Dieselkraftwerk's location is guarded by a couple of enemies, including a Zerstorer. You can either sneak past them or fight.
It's worth keeping in mind that if you do decide to go in loud, the enemies can be dispatched more easily by firing through tight spots between cover or using a pipe just below the road leading to the gate.
After you've entered the bunker, go through its garage and into the hangar with another Zerstorer, which you should consider sneaking past.
Then, simply follow the mission waypoint until you reach a door with a keypad. Get past it, and the Dieselkraftwerk will be waiting inside a weapon case in the next room.
Wolfenstein: Youngblood is out now on PC, via Steam, Xbox One, PS4 and Nintendo Switch. It will arrive on Google Stadia at a later date.