A device for cleaning of polluted gas from a combustion engine, includes a centrifugal separator with a centrifuge rotor arranged to cause the polluted gas to rotate. The centrifuge rotor comprises a stack of truncated conical separating discs disposed at mutual spacing so they delimit intermediate spaces between them for the gas to flow through. An outlet chamber is disposed centrally within the stack of separating discs, whereby the centrifuge rotor is configured for counterflow separation. The centrifugal separator comprises a gas outlet which communicates with the outlet chamber. The stack of separating discs is disposed for rotation in a space formed within the combustion engine and arranged to receive the polluted gas, to which end the intermediate spaces between the separating discs communicate directly with the space, and the gas outlet is arranged to conduct the cleaned gas out from the space through a wall which delimits the space.