Method for calculating the no2 content at the inlet of a selective reduction catalyst and device for the implementation of this method

A method for the calculation of the nitrogen dioxide content at the inlet of a selective catalytic reduction device (22) of an exhaust system (4) of an internal combustion engine, said exhaust system (4) comprising:

• a gas exhaust pipe (10),
• upstream of the selective catalytic reduction device (22), a tank for a reducing agent and means for injecting (18) the reducing agent into the exhaust pipe (10),
• a first sensor (20) intended to measure the concentration of nitrogen oxides present in the exhaust pipe (10) upstream of the selective catalytic reduction device (22), and
• a second sensor (24) intended to measure the concentration of nitrogen oxides present in the exhaust pipe (10) downstream of the selective catalytic reduction device (22),
• characterized in that it comprises the following stages:
• halting the injection of reducing agent into the exhaust pipe (10),
• measuring the concentration of nitrogen oxides present in the exhaust pipe (10) upstream and downstream of the selective catalytic reduction device (22) during a period of time,
• calculating the amount of nitrogen dioxide accumulated in the selective catalytic reduction device (22) during said period of time from the change in the concentration of nitrogen oxides measured upstream and downstream of the selective catalytic reduction device (22), and
• determining the nitrogen dioxide content upstream of the selective catalytic reduction device (22) from the calculated amount of nitrogen dioxide accumulated per unit of time.