Metering System for Spraying a Urea Solution into the Exhaust Gas Stream of an Internal Combustion Engine

Abstract

A metering system for injecting a urea solution into the exhaust gas flow of an internal combustion engine for selective catalytic reduction, and method for controlling the injecting of a urea solution by means of compressed air, wherein the metering system is connected to a urea solution tank and a compressed air supply, wherein the metering system comprises at least one nozzle through which the urea solution can be injected into the exhaust gas flow by compressed air, including an electronic control unit and air valve for regulating the pressure and/or the quantity of air and/or the valve opening times of the compressed air supply and a sensor for measuring the pressure and/or the quantity of air disposed in the compressed air supply between the air valve and the nozzle so that the quantity of compressed air fed in for atomizing the urea solution is controlled.

What is claimed is: 
     
         1 . A metering system for spraying a urea solution into an exhaust gas stream ( 9 ) of an internal combustion engine for selective catalytic reduction comprising:
 a urea solution tank ( 1 ) for delivering a urea solution;   at least one nozzle ( 5 ) through which said urea solution is sprayed into said exhaust gas stream;   a compressed air supply ( 6 ) operatively connected to said nozzle ( 5 );   an air valve ( 7 ) operatively connected to said at least one nozzle; and   a sensor positioned between said air valve ( 7 ) and said at least one nozzle ( 5 ) for measuring the pressure and/or the amount of air present in the compressed air supply,   at least one selective catalytic reduction catalyst ( 10 ),   a sensor positioned rearward the selective catalytic reduction catalyst ( 10 ) measuring the NOx-portion of the exhaust gas,   
       wherein said sensor, is in operative communication with said air valve ( 7 ) and said air valve ( 7 ) regulates the pressure and/or the amount of air and/or the valve opening times of the compressed air supply ( 6 ) and further wherein said at least one nozzle ( 5 ) is an outward-mixing binary nozzle, 
       wherein said urea solution is sprayed into said exhaust gas stream ahead said at least one selective catalytic reduction catalyst. 
     
     
         2 . A metering system according to  claim 1 , wherein the air valve ( 7 ) is a proportional control valve. 
     
     
         3 . A metering system according to  claim 1 , wherein the sensor is a pressure sensor ( 16 ). 
     
     
         4 . A metering system according to  claim 1 , wherein the metering system has means for calculating the exhaust gas mass stream or a sensor ( 11 ) for measuring the exhaust gas mass stream. 
     
     
         5 . A metering system according to  claim 1 , wherein the metering system has a sensor ( 17 ) for measuring the exhaust gas temperature. 
     
     
         6 . A metering system according to  claim 1 , wherein the compressed air supply ( 6 ) has a butterfly valve ( 15 ). 
     
     
         7 . A metering system according to  claim 1 , wherein the metering system has a metering pump ( 3 ) for supplying the urea solution. 
     
     
         8 . A metering system according to  claim 1 , wherein a connecting line ( 13 ) is arranged between a urea line ( 4 ) and a line of the compressed air supply, whereby the connecting line ( 13 ) has a nonreturn valve ( 14 ). 
     
     
         9 . A metering system according to  claim 1 , wherein the metering system has a compressed air compressor. 
     
     
         10 . A metering system according to  claim 1 , wherein the metering system has a control device ( 12 ), by means of which the air valve ( 7 ) and/or a butterfly valve ( 15 ) and/or a metering pump ( 3 ) and/or a compressed air compressor can be controlled based on the measured value/s acquired by the sensor/s ( 11 ,  16 ,  17 ). 
     
     
         11 . A metering system according to  claim 1 , wherein the metering system has a urea solution tank ( 1 ). 
     
     
         12 . A method for controlling spraying of a urea solution by means of compressed air into the exhaust gas stream ( 9 ) of an internal combustion engine for selective catalytic reduction, wherein the amount of compressed air that is fed to the urea solution for atomization is controlled at each operating point based on the operating parameters of exhaust gas temperature and exhaust gas mass stream and is reduced to the minimum amount of air that is required in each case, so that the droplet quality of the sprayed urea solution is sufficient for the action of the catalyst. 
     
     
         13 . A method according to  claim 12 , wherein when the spraying of the urea solution is interrupted or completed, the urea solution is cleaned from the urea solution-carrying lines by means of compressed air. 
     
     
         14 . A method according to  claim 12 , wherein the spraying of the urea solution is interrupted or completed by turning off a metering pump ( 3 ). 
     
     
         15 . A method according to  claim 12 , wherein an activation of at least one metering pump ( 3 ) and/or at least one compressed air compressor and/or at least one air-control valve ( 7 ) is carried out based on the operating parameters of exhaust gas temperature and exhaust gas mass stream. 
     
     
         16 . A Method according to  claim 13 , wherein the spraying of the urea solution is interrupted or completed by turning off a metering pump ( 3 ). 
     
     
         17 . A Method according to  claim 13 , wherein an activation of at least one metering pump ( 3 ) and/or at least one compressed air compressor and/or at least one air-control valve ( 7 ) is carried out based on the operating parameters of exhaust gas temperature and exhaust gas mass stream. 
     
     
         18 . A Metering system according to  claim 2 , wherein the sensor is a pressure sensor ( 16 ). 
     
     
         19 . A Metering system according to  claim 4 , wherein the sensor is a pressure sensor ( 16 ). 
     
     
         20 . A Metering system according to  claim 10 , wherein the sensor is a pressure sensor ( 16 ).