A piston engine and a method for controlling a diesel-type piston engine including at least one combustion chamber formed by a cylinder, a movably arranged piston in each cylinder, which piston is connected to a crankshaft, an injection device designed to inject fuel directly into the combustion chamber and turbo system comprising a low pressure turbo and a high pressure turbo. The thermal efficiency of the internal combustion is increased while requirements relating to nitrogen oxide and soot particle emissions continue to be maintained.