Method and apparatus for controlled introduction of a reducing agent into a nitrogen oxide-containing exhaust gas

#This application is a Continuation of International Application Ser. No. PCT/DE94/00463, filed Apr. 27, 1994.

#1. Field of the Invention

#The invention relates to a method and an apparatus for the controlled introduction of a reducing agent into a nitrogen oxide-containing exhaust gas from an internal combustion engine, having a catalytic converter built into the exhaust line for reducing nitrogen oxide.

#FIG. 1 is a schematic and block circuit diagram of an exhaust line of a 300 kW charge-air-cooled Diesel engine with controlled introduction of a reducing agent into a nitrogen oxide-containing exhaust gas;

#FIG. 2 is a diagram showing a qualitative course of catalytic activity of a deNO.sub.x catalyst as a function of temperature;

#FIG. 3 is a diagram showing a qualitative course of a specific storage capacity C.sub.R of a deNO.sub.x catalyst for a reducing agent as a function of the temperature;

#Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen an exhaust line 2 of a 300 kW charge-air-cooled Diesel engine 4 with a measurement location 5 connected to the Diesel engine 4. A further measurement location 6, a catalytic converter 8 and an additional measurement location 20, in that order, are installed in the exhaust line 2. As seen in the flow direction of an exhaust gas 10, the catalytic converter 8 includes, in the following order, an inlet chamber 12, a hydrolysis catalyst 14, a deNO.sub.x catalyst 16, and an oxidation catalyst 18. Besides the exhaust line 2, a Bunsen burner exhaust line 22 and a reducing agent supply line 32 are also connected to the inlet chamber 12 of the catalytic converter 8. The supply line 32 has an adjustable injection valve 24 for the controlled addition of a reducing agent 26. Hot exhaust gas 36 of a Bunsen burner 28 is fed as needed through the Bunsen burner exhaust line 22 into the inlet chamber 12. The reducing agent 26, which is an aqueous urea solution in the exemplary embodiment, is kept on hand in a reducing agent tank 30 and is supplied to the injection valve 24 through the reducing agent supply line 32. The reducing agent 26 is injected into the inlet chamber 12 through the use of the injection valve 24, within a zone that is demarcated from the walls of the inlet chamber 12 by perforated plates 34. The exhaust gas 10 and optionally the Bunsen burner exhaust gas 36 enter the inlet chamber 12 outside this zone. The exhaust gases 10, 36 pass through holes in the perforated plates 34 and in the process entrain the reducing agent 26 injected into the inlet chamber 12. This prevents the reducing agent 26 from disadvantageously being deposited on the walls of the inlet chamber 12.

#In order to adjust the rate M.sub.R of reducing agent injected into the exhaust gas 10 in metered fashion, a control unit 38 with a microprocessor subunit 40 is provided. The control unit 38 has inputs E.sub.1 through E.sub.4, through which it detects operation-relevant parameters, the knowledge of which is necessary for adjustment of the suitable reducing agent rate M.sub.R. Through the use of the measurement location 5, which includes a number of sensors, the air flow rate, the governor rod path, which is equivalent to the position of the Diesel injection device, the charge pressure, and the rpm of the Diesel engine 4 are detected. These data are applied to the input E.sub.1.

#The operation-relevant parameters of the exhaust gas 10 (which are measured, for instance, through the use of the further measurement location 6), in this case its temperature, pressure and flow rate, are applied to the input E.sub.2. In the exemplary embodiment, the flow rate and the pressure are calculated from the parameters of the Diesel engine 4 that are supplied to the input E.sub.1. It would also be possible for the pressure as well as the flow rate to be measured through separate sensors in the further measurement location 6.