A wellbore fluid including a peroxide degradable polymer and an encapsulated peroxide source. A ramjet 6b is attached to a tube 3 that is able to rotate around the encircled part of the fuselage. An intake camshaft that actuates the intake valve extends through the engine body and toward the outer area beyond the outer surface. A refuelling venting conduit is branched off after the first filter stage and is communicatable with the atmosphere or the tank interior.