This thesis reports on the influence of an aqueous H2O2 solution on the combustion process and the pollutant emissions of a direct injection naturally aspirated diesel engine. The effect of a H2O2/water addition into a flow reactor, into the exhaust gas and into the combustion chamber of a diesel engine was monitored by the measurement of gaseous (HC, CO, NOx, O2) and solid exhaust gas constituents. The effect on solid exhaust gas constituents was observed by the means of mass-, size- and number-related measurement techniques. Additional experiments with cycle resolved spectroscopy and pressure indication were performed in the case of H2O2/water injection into the combustion chamber. The results show that a significant decrease of gaseous and solid pollutant emissions of a diesel engine is possible with H2O2/water addition. Particularly the strong effect of a H2O2/water injection into the combustion chamber on soot oxidation indicates that OH radicals play an important role in the process of soot oxidation wi in the combustion chamber.