Engine maker Rolls-Royce has confirmed that it is in discussions, together with German car maker Daimler, about the possibility of acquiring engine group Tognum."Constructive discussions with the supervisory board and management board of Tognum are being held," Rolls said.Daimler already owns a 28.4% stake in Tognum.The announcement came in response to a report in Manager Magazine that said the two companies are planning to buy stakes of 50% each in Tognum.Tognum supplies engines for the marine, power generation and industrial sectors.