Exhaust gas treatment system

Abstract

An exhaust gas treatment system includes an exhaust passage through which exhaust gas from an internal combustion engine is allowed to flow, a selective catalytic reduction catalyst provided in the exhaust passage, a mixing chamber provided upstream of the selective catalytic reduction catalyst in the exhaust passage as viewed in the direction of exhaust gas flow, a fuel injection valve for injection of fuel, an air injection valve for injection of air, and a urea water injection valve for injection of urea water. The fuel injection valve, the air injection valve and the urea water injection valve each has an injection port directed to the mixing chamber.

What is claimed is: 
     
         1 . An exhaust gas treatment system, comprising:
 an exhaust passage through which exhaust gas from an internal combustion engine is allowed to flow;   a selective catalytic reduction catalyst provided in the exhaust passage,   a mixing chamber provided upstream of the selective catalytic reduction catalyst in the exhaust passage as viewed in the direction of exhaust gas flow;   a fuel injection valve for injection of fuel;   an air injection valve for injection of air; and   a urea water injection valve for injection of urea water,   wherein the fuel injection valve, the air injection valve and the urea water injection valve each has an injection port directed to the mixing chamber.   
     
     
         2 . The exhaust gas treatment system according to  claim 1 , wherein the fuel injection valve, the air injection valve and the urea water injection valve are arranged parallel to one another, and the air injection valve is located between the fuel injection valve and the urea water injection valve. 
     
     
         3 . The exhaust gas treatment system according to  claim 1 , wherein the fuel injection valve, the air injection valve and the urea water injection valve are integrated in one unit. 
     
     
         4 . The exhaust gas treatment system according to  claim 1 , wherein the injection directions of the fuel injection valve, the air injection valve and the urea water injection valve are substantially parallel to the direction of exhaust gas flow in the exhaust passage. 
     
     
         5 . The exhaust gas treatment system according to  claim 1 , further comprising a partition member provided in the exhaust passage, the partition member forming therein the mixing chamber and having openings for introducing exhaust gas from the outside to the inside of the mixing chamber. 
     
     
         6 . The exhaust gas treatment system according to  claim 5 , wherein the partition member is of a cylindrical shape and concentric with the exhaust passage. 
     
     
         7 . The exhaust gas treatment system according to  claim 5 , wherein the partition member is of a cylindrical shape, the upstream end of the partition member being closed by an end wall where the fuel injection valve, the air injection valve and the urea water injection valve are mounted, the downstream end of the partition member being opened. 
     
     
         8 . The exhaust gas treatment system according to  claim 1 , wherein the selective catalytic reduction catalyst is integrated with a particulate filter for capturing particulate matter. 
     
     
         9 . The exhaust gas treatment system according to  claim 8 , further comprising a controller by which the fuel injection valve is operated so that fuel is injected when the particulate filter needs to be regenerated. 
     
     
         10 . The exhaust gas treatment system according to  claim 1 , further comprising a controller by which the fuel injection valve and the urea water injection valve are operated so that fuel and urea water are injected simultaneously. 
     
     
         11 . The exhaust gas treatment system according to  claim 1 , further comprising a controller by which the fuel injection valve and the urea water injection valve are operated so that urea water is injected after injection of fuel. 
     
     
         12 . The exhaust gas treatment system according to  claim 1 , further comprising a baffle plate provided between the mixing chamber and the selective catalytic reduction catalyst for mixing of gases flowing therethrough. 
     
     
         13 . The exhaust gas treatment system according to  claim 1 , wherein at least two of the injection ports has annular cross section, and the injection ports are all concentric with each other.