An arrangement and a method for controlling a combustion engine, e.g. of the type called HCCI engine. A control unit for controlling the self-ignition of the fuel mixture towards an optimum crankshaft angel (cad.sub.iopt) within a load range (L.sub.tot). The load range (L.sub.tot) can be divided into at least two subranges (L.sub.I, L.sub.II) and the control unit is adapted to controlling the self-ignition of the fuel mixture towards an optimum crankshaft angle (cad.sub.iopt) within a first subrange (L.sub.I) by means of a strategy (I) which entails a variable amount of hot exhaust gases being supplied to or retained in the combustion chamber, and within a second subrange (L.sub.II) by means of another strategy (II) which entails the effective compression ratio (c) in the cylinder being varied.