We will introduce two methods with which hydrogen peroxide (H2O2) is injected into the combustion chamber of a DI Diesel engine during main time of combustion. One method is using a second injection system to inject the H2O2 and the other method is the injection of a fuel-H2O2 emulsion into the combustion chamber. Hereby the emission of soot can be considerably reduced without a large influence to NOx, even with the second method a reduction of NOx is measured. From calculations on soot kinetics and measurements it is known that the majority of soot is already being oxidized within the cylinder itself. Considering the high temperatures during the combustion, it is mainly the OH radical that leads to soot oxidation. By injecting H2O2 and in this way increasing the concentration of OH later on during the combustion, soot can almost completely be reduced provided that there is an ideal mixture.