Method for monitoring the formation of nitrogen dioxide at an oxidation catalytic converter, and exhaust system

A method for monitoring formation of nitrogen dioxide at an oxidation catalytic converter arranged in an exhaust gas system of a vehicle, in which, by an exhaust gas aftertreatment device, a content of nitrogen oxides in an exhaust gas is reduced by converting the nitrogen oxides, and the content of nitrogen oxides in the exhaust gas is measured, comprising the steps of:

• the conversion of the nitrogen oxides by the exhaust gas aftertreatment device that corresponds to a first exhaust gas volume flow through the oxidation catalytic converter is measured;
• the exhaust gas volume flow is varied;
• and
• a changing of the conversion of the nitrogen oxides by the exhaust gas aftertreatment device occurring with the variation of the exhaust gas volume flow is determined;
• wherein, based on the respective conversion of nitrogen oxides with the different exhaust gas volume flows through the oxidation catalytic converter, the formation of nitrogen dioxide at the oxidation catalytic converter is inferred based on a predetermined relationship between the conversion of nitrogen oxides and a proportion of nitrogen dioxide in the nitrogen oxides in the exhaust gas;
• wherein the exhaust gas volume flow through the oxidation catalytic converter is varied by varying a proportion of a low-pressure exhaust gas recirculation rate of a total exhaust gas recirculation rate which is made up of a high-pressure exhaust gas recirculation rate and the low-pressure exhaust gas recirculation rate;
• and wherein the low-pressure exhaust gas recirculation rate is increased and the high-pressure exhaust gas recirculation rate is reduced for a constant total exhaust gas recirculation rate.