Method and combustion system for improving combustion characteristics for a direct injected compression ignition engine

The invention relates to a method for regeneration of a nitrogen oxide storage catalyst (160) for a direct injected compression ignition engine comprising a controllable fuel injection system (170) and means (120, 125, 140) for controlling swirl ratio. According to the invention, there is provided the consecutive steps of: activating the swirl increasing means (120, 125, 140); and controlling the controllable fuel injection means to give a number of small part-injections during an expansion stroke of an engine cylinder.