Control method for controlling an exhaust aftertreatment system and exhaust aftertreatment system

An exhaust aftertreatment system for controlling an NO2/NO ratio in exhaust gas from an engine, comprising:

• an oxidation catalyst in which constituents of the exhaust gas are oxidized;
• a diesel particulate filter;
• a selective-catalytic-reduction catalyst in which constituents of the exhaust gas are deoxidized by a group of possible chemical reactions of different type between the constituents of the exhaust gas and catalytic material arranged in the selective-catalytic-reduction catalyst, wherein the exhaust gas flows from the oxidation catalyst to the selective-catalytic-reduction catalyst;
• means for controlling flow of the exhaust gas through the oxidation catalyst depending on at least one desired ratio among a pair of the constituents, wherein the exhaust gas enters the selective-catalytic-reduction catalyst With the at least one desired ratio among the pair of the constituents;
• means for establishing the at least one desired ratio among the pair of the constituents at the input of the selective-catalytic-reduction catalyst depending on a soot load in a particulate filter arranged between the oxidation catalyst and the selective-catalytic-reduction catalyst and depending on an amount of NO2 which is generated in the particulate filter;
• means for establishing a predetermined reaction temperature or temperature range in the selective-catalytic-reduction catalyst wherein the probability that one specific chemical reaction out of the group of possible different chemical reactions between the constituents of the exhaust gas and the catalyst material in the selective-catalytic-reduction catalyst will take place is increased by inputting the exhaust gas into the selective-catalytic-reduction catalyst, wherein the reaction probability for the selected specific chemical reaction is higher than the reaction probability for each one of the other chemical reactions which are not selected.

A non-transitory computer readable medium, comprising a program for performing a method comprising:

• controlling the flow of exhaust gas through an oxidation catalyst depending on at least one desired ratio among the pair of the constituents, wherein the exhaust gas enters a selective-catalytic-reduction catalyst with the at least one desired ratio among the pair of the constituents;
• establishing the at least one desired ratio among the pair of the constituents at an input of the selective-catalytic-reduction catalyst;
• selecting a predetermined reaction temperature or temperature range and establishing it in the selective-catalytic-reduction catalyst wherein the probability is increased that one specific chemical reaction out of the group of possible different chemical reactions between the constituents of the exhaust gas and the catalyst material in the selective-catalytic-reduction catalyst will take place by Inputting the exhaust gas into the selective-catalytic-reduction catalyst, wherein the reaction probability for the selected specific chemical reaction is higher than the reaction probability for each one of the other chemical reactions which are not selected;
• and
• establishing the ratio among the constituents depending on the amount of soot a soot load in a particulate filter arranged between the oxidation catalyst and the selective-catalytic-reduction catalyst and depending on an amount of NO2 which is generated in the particulate filter.